424B5

424B5 1 d111359d424b5.htm 424B5 424B5

As Filed Pursuant to Rule 424(b)(5)
Registration No. 333-288884

PROSPECTUS SUPPLEMENT

(To Prospectus Dated June 30, 2026)

LOGO

6,400,000

American Depositary Shares

Representing Ordinary Shares

We are offering 6,400,000 of our American Depositary Shares (“ADSs”), each representing one ordinary share, €0.01 nominal value per share, in a public offering.

Our ordinary shares are listed on the regulated market of Euronext in Paris (“Euronext Paris”) under the symbol “ABVX.” Our ADSs are listed on The Nasdaq Global Market (“Nasdaq”) under the symbol “ABVX.” On June 30, 2026, the last reported sale price of our ordinary shares on Euronext Paris was €115.50 per ordinary share and the last reported sale price of our ADSs on Nasdaq was $133.26 per ADS.

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks that we have described beginning on page S-9 of this prospectus supplement under the caption “Risk Factors” and under the caption “Risk Factors” on page 6 of the accompanying prospectus and in our most recent Annual Report on Form 20-F and any other reports or documents incorporated by reference into this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any U.S. state or other securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.


	Per ADS		Total
Public offering price	$	125.0000	$	800,000,000
Underwriting discounts and commissions(1)	$	5.9375	$	38,000,000
Proceeds to us (before expenses)	$	119.0625	$	762,000,000

(1)	We refer you to “Underwriting” beginning on page S-29 of this prospectus supplement for additional information regarding underwriting compensation.

Delivery of the ADSs is expected to be made on or about July 6, 2026 (the “initial settlement date”), through the book-entry facilities of The Depository Trust Company. We have granted an option to the underwriters, exercisable on or before the initial settlement date, to purchase up to an aggregate of 960,000 additional ADSs at the public offering price.

Joint Bookrunning Managers


Leerink Partners		Morgan Stanley		Piper Sandler		Guggenheim Securities

Bookrunning Manager

LifeSci Capital

Lead Manager

Van Lanschot Kempen

Prospectus Supplement dated June 30, 2026

TABLE OF CONTENTS

Prospectus Supplement


	Page
ABOUT THIS PROSPECTUS SUPPLEMENT		S-ii
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		S-iv
PROSPECTUS SUMMARY		S-1
RISK FACTORS		S-9
USE OF PROCEEDS		S-12
CAPITALIZATION		S-13
DILUTION		S-15
TAXATION		S-17
UNDERWRITING		S-29
MATERIAL CHANGES		S-40
ENFORCEMENT OF CIVIL LIABILITIES		S-41
LEGAL MATTERS		S-43
EXPERTS		S-43
WHERE YOU CAN FIND ADDITIONAL INFORMATION		S-44
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		S-45

Prospectus


	PAGE
ABOUT THIS PROSPECTUS		1
PROSPECTUS SUMMARY		3
RISK FACTORS		6
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		7
USE OF PROCEEDS		9
SELLING SECURITY HOLDERS		10
PLAN OF DISTRIBUTION		11
DESCRIPTION OF SHARE CAPITAL		13
LIMITATIONS AFFECTING SHAREHOLDERS OF A FRENCH COMPANY		32
DESCRIPTION OF AMERICAN DEPOSITARY SHARES		34
DESCRIPTION OF WARRANTS		45
DESCRIPTION OF DEBT SECURITIES		46
TAXATION		53
LEGAL MATTERS		54
EXPERTS		54
ENFORCEMENT OF CIVIL LIABILITIES		55
WHERE YOU CAN FIND MORE INFORMATION		57
INCORPORATION OF DOCUMENTS BY REFERENCE		58
EXPENSES ASSOCIATED WITH REGISTRATION		59

Neither we nor any of the underwriters have authorized anyone to provide any information other than that contained in this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us to which we have referred you. When you make a decision about whether to invest in our ADSs, you should not rely upon any information other than the information in this prospectus supplement. We take no responsibility for, and provide no assurances as to the reliability of, any other information that others may give you.

S-i

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is part of an automatic shelf registration statement that we filed with the Securities and Exchange Commission (the “SEC”) using a “shelf” registration process available to us as a “well-known seasoned issuer,” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”) and consists of two parts. The first part is this prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering and also adds to and updates information contained in the accompanying prospectus. The second part, the accompanying prospectus, including the documents incorporated by reference, gives more general information, some of which may not be applicable to this offering. Generally, when we refer to the “prospectus” we are referring to both parts combined.

If information in this prospectus supplement is inconsistent with the accompanying prospectus or with any document incorporated by reference that was filed with the SEC before the date of this prospectus supplement, you should rely on this prospectus supplement. If any statement in this prospectus supplement or the accompanying prospectus is inconsistent with a statement in another document that is incorporated by reference into this prospectus and having a later date, the statement in the document having the later date modifies or supersedes the earlier statement. This prospectus supplement, the accompanying prospectus and the documents incorporated by reference into each include important information about us, the ordinary shares (including in the form of ADSs) being offered and other information that you should know before investing in our ordinary shares (including in the form of ADSs). You should also read and consider information in the documents we have referred you to in the sections of this prospectus supplement and the accompanying prospectus entitled “Incorporation of Certain Information by Reference” and “Where You Can Find Additional Information.”

You should assume that the information in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front of the respective document and that any information that we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus supplement or the accompanying prospectus or the time of any sale of securities. Our business, financial condition, liquidity, results of operations and prospects may have changed since those dates.

This prospectus supplement and the accompanying prospectus contain summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. In such instances, such summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated herein by reference as exhibits to the registration statement, and you may obtain copies of those documents as described below under the sections entitled “Incorporation of Certain Information by Reference” and “Where You Can Find Additional Information.”

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

We are not making offers to sell or solicitations of offers to buy our ordinary shares (including in the form of ADSs) in any jurisdiction in which an offer or solicitation is not permitted or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

For investors outside the United States: We have not done anything that would permit this offering or possession or distribution of this prospectus supplement in any jurisdiction where action for that purpose

S-ii

is required, other than in the United States. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the securities described herein and the distribution of this prospectus supplement outside the United States.

Owning our securities may subject you to tax consequences both in France and in the United States. You should read the tax discussion in this prospectus supplement fully, though this prospectus supplement and the accompanying prospectus may not describe these tax consequences fully. Each prospective investor is urged to consult its own tax advisor about the tax consequences to it of an investment in our securities in light of the investor’s own circumstances. In addition, your ability to enforce civil liabilities under U.S. federal securities laws may be affected adversely by the fact that we are incorporated under the laws of France, many of the members of our board of directors and experts named in this prospectus are residents of France or elsewhere outside of the United States, and a substantial portion of our assets and the assets of such persons are located outside the United States. See “Enforcement of Civil Liabilities.”

Unless otherwise indicated, all references in this prospectus supplement to “Abivax,” “the Company,” “our Company,” “we,” “us” and “our” refer to Abivax SA and its consolidated subsidiary, taken as a whole.

We are an “emerging growth company” as that term is used in the Jumpstart Our Business Startups Act of 2012 (the “JOBS Act”) and, as such, have elected to comply with certain reduced public company reporting requirements.

We prepare our consolidated financial statements in accordance with International Financial Reporting Standards (“IFRS”) as issued by the International Accounting Standards Board (“IASB”). Our financial statements are presented in euros and, unless otherwise specified, all monetary amounts printed in this prospectus are in euros.

All references in this prospectus supplement to “$” and “U.S. dollars” mean U.S. dollars and all references to “€” and “euros” mean euros, unless otherwise noted. In various places throughout this prospectus supplement, we show financial amounts in both U.S. dollars and euros. Unless otherwise noted, these translations, which are provided solely for convenience, are made at the exchange rate of €1.00 = $1.1498, the exchange rate as reported by the European Central Bank on March 31, 2026.

Throughout this prospectus supplement, references to ADSs mean ADSs or ordinary shares represented by such ADSs, as the case may be.

S-iii

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference contain “forward-looking statements” within the meaning of applicable federal securities laws, including Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the Private Securities Litigation Reform Act of 1995. All statements other than present and historical facts and conditions, including statements regarding our future results of operations and financial position, business strategy, plans and our objectives for future operations, are forward-looking statements. When used in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference, the words “anticipate,” “believe,” “can,” “could,” “estimate,” “expect,” “intend,” “is designed to,” “may,” “might,” “objective,” “plan,” “potential,” “predict,” “should,” “will,” “would” or the negative of these and similar expressions identify forward-looking statements. Forward-looking statements include, but are not limited to, statements about:

•

the prospects of attaining, maintaining and expanding marketing authorization for our lead drug candidate, obefazimod;

•

the potential attributes and clinical advantages of obefazimod and our future drug candidates;

•

the initiation, timing, progress and results of our preclinical and clinical trials (and those conducted by third parties) and other research and development programs;

•

the timing of the availability of data from our clinical trials, including our Phase 2b trial of obefazimod in Crohn’s disease;

•

the timing of and our ability to advance drug candidates through clinical development;

•

the timing or likelihood of regulatory meetings and filings;

•

the timing of and our ability to obtain and maintain regulatory approvals for obefazimod and any of our future drug candidates;

•

our ability to identify and develop new drug candidates from our preclinical studies;

•

our ability to develop sales and marketing capabilities and transition into a commercial-stage company;

•

the effects of increased competition as well as innovations by new and existing competitors in our industry;

•

our ability to enter into strategic relationships or partnerships;

•

our ability to obtain, maintain, protect and enforce our intellectual property rights and proprietary technologies and to operate our business without infringing the intellectual property rights and proprietary technology of third parties;

•

our estimates regarding expenses, future revenues, capital requirements and the need for additional financing;

•

the impact of government laws and regulations;

•

our competitive position;

•

unfavorable conditions in our industry, the global economy or global supply chain, including financial and credit market fluctuations, international trade relations, political turmoil, natural catastrophes, warfare (such as the Russia-Ukraine war or the conflict in the Middle East), and terrorist attacks;

•

risks related to this offering, including our ability to consummate this offering, and our expected use of the net proceeds from such offering; and

•

other risks and uncertainties indicated in this prospectus supplement and the documents incorporated by reference herein, including those under the heading “Risk Factors,” and the other documents filed or to be filed with the SEC by us.

S-iv

Such statements are subject to risks and uncertainties, and actual results may differ materially from those expressed or implied in the forward-looking statements due to various factors, including, but not limited to, those identified under the caption “Risk Factors” in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference. As a result of these factors, we cannot assure you that the forward-looking statements in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference will prove to be accurate. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame or at all. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law. In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus supplement, the accompanying prospectus and the documents incorporated by reference, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

Many important factors, in addition to the factors described in this prospectus supplement and the accompanying prospectus, which may adversely affect such forward-looking statements are set forth in Part I, Item 3.D. of our Annual Report on Form 20-F for the year ended December 31, 2025 (the “Annual Report”), as updated by our subsequent Reports on Form 6-K and the other documents incorporated by reference in this prospectus supplement and the accompanying prospectus. See “Where You Can Find Additional Information” and “Incorporation of Certain Information by Reference.” Many of these risks, uncertainties and assumptions are beyond our control, and may cause our actual results and performance to differ materially from our expectations. Accordingly, you should not place undue reliance on any forward-looking statements contained or incorporated by reference in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference.

You should read this prospectus supplement, the accompanying prospectus and the documents we incorporate by reference completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

S-v

PROSPECTUS SUMMARY

This summary highlights selected information about us and this offering. This summary is not complete and may not contain all of the information that is important to you. We encourage you to read this prospectus supplement and the accompanying prospectus, including any information incorporated by reference into this prospectus supplement and the accompanying prospectus, in their entirety.

Our Company

We are a clinical-stage biotechnology company focused on developing therapeutics that harness the body’s natural regulatory mechanisms to stabilize the immune response in patients with chronic inflammatory diseases. We focus on indications where existing treatments have left patients with significant unmet needs, and where we believe our investigational agents have the potential to be meaningfully differentiated from currently available therapies. Our initial focus is on inflammatory bowel diseases (“IBD”), chronic conditions involving inflammation of the gastrointestinal tract, of which the two most common forms are ulcerative colitis (“UC”) and Crohn’s disease.

We believe our lead drug candidate, obefazimod, is differentiated from competing approaches for the treatment of IBD via its novel mechanism of action. Obefazimod was demonstrated to specifically enhance the expression of a single micro-RNA, miR-124, which plays a critical role in the regulation of the inflammatory response. In the context of inflammation, miR-124 is a natural regulator of the inflammatory response, controlling progression of inflammation and restoring homeostasis of the immune system, without causing broader immunosuppression. In contrast to currently available advanced therapies, prescribed post-conventional therapies, some of which target only a single cytokine or pathway, miR-124 modulates the expression of several key cytokines and pathways. Modulating multiple inflammatory pathways simultaneously may lead to more durability of efficacy results over the long-term, which is critical in lifelong conditions such as IBD, potentially differentiating obefazimod from currently available IBD treatments.

Recent Developments

Royalty Certificate Repurchase

On May 4, 2026, we entered into a purchase agreement with the royalty certificate holders named therein (the “Holders”) to repurchase all of the royalty certificates issued to them on September 7, 2022. We repurchased the royalty certificates in full by paying an aggregate consideration of $90.0 million, of which $45.0 million was paid in cash and $45.0 million was paid in shares through the issuance of 403,347 ordinary shares, including in the form of ADSs, to the Holders in a private placement that was exempt from registration under the Securities Act (the “Royalty Certificate Repurchase”). On May 7, 2026, we filed a prospectus supplement for the purpose of registering the offer and resale from time to time of up to 403,347 ADSs held by the Holders identified in such prospectus supplement.

Positive Topline Results from Part 2 of Our Phase 3 ABTECT 44-Week Maintenance Trial

On June 29, 2026, we announced positive topline results from Part 2 of our Phase 3 ABTECT 44-week maintenance trial evaluating obefazimod, our potential first-in-class oral miR-124 enhancer, in moderate to severely active UC. Part 2 of the Phase 3 maintenance trial enrolled patients who either did not achieve clinical response following induction treatment or who experienced disease relapse during the re-randomized maintenance trial (Part 1), expanding both the efficacy and safety results in a more refractory patient population than the registrational maintenance cohort. The additional safety results generated through Part 2 expand the Phase 3 maintenance database and provide important context for interpreting the safety findings reported following the maintenance Part 1 readout.

S-1

Among patients who failed to achieve clinical response after 8 weeks of induction, continued treatment with obefazimod resulted in clinically meaningful rates of clinical, endoscopic, and combined histologic-endoscopic endpoints at Week 44. Patients treated continuously with 50 mg obefazimod demonstrated the strongest outcomes across all endpoints, including clinical remission (37.2%), clinical response (61.5%), endoscopic improvement (48.0%), Histologic-Endoscopic Mucosal Improvement (“HEMI”) (44.6%), and endoscopic remission (34.5%). These findings suggest that a clinically meaningful proportion of patients who do not initially respond may still derive substantial benefit from longer treatment exposure.


Part 2 Induction Non-Responders – Exploratory Endpoints
	25 mg (N=81)	50 mg (N=148)
Clinical Remission	23.5%	37.2%
Clinical Response	50.6%	61.5%
Endoscopic Improvement	28.4%	48.0%
HEMI	23.5%	44.6%
Endoscopic Remission	22.2%	34.5%

Among patients who relapsed during Part 1 of the maintenance trial, re-treatment with 50 mg obefazimod resulted in meaningful rates of clinical remission, clinical response, endoscopic improvement, HEMI and endoscopic remission by Week 44. Patients who achieved clinical response with obefazimod during induction and relapsed after being re-randomized to placebo in Part 1 of the maintenance trial were treated with open-label 50 mg obefazimod and achieved clinical response and remission rates of 69.7% and 45.0%, respectively, while patients who relapsed on 25 mg and escalated to 50 mg achieved clinical response and clinical remission rates of 66.7% and 45.5%, respectively. These findings demonstrate the potential for obefazimod to re-establish disease control following relapse and support a flexible maintenance treatment strategy.


Part 1 Relapsers – Exploratory End+points
	Placebo è 50 mg (N=109)	25 mg è 50 mg (N=33)
	50 mg	50 mg
Clinical Remission	45.0%	45.5%
Clinical Response	69.7%	66.7%
Endoscopic Improvement	54.1%	45.5%
HEMI	47.7%	39.4%
Endoscopic Remission	32.1%	24.2%

S-2

In Part 2, four total non-melanoma skin cancers (“NMSC”) events were reported, two in the 25 mg arm and two in the 50 mg arm which all occurred in patients with established NMSC risk factors including advanced age, thiopurine use, prior skin cancer history and failure of multiple prior advanced therapies. There were also two non-NMSC malignancies reported in the 50 mg arm, both deemed unrelated to obefazimod by the study investigators. The results are summarized below.


Summary Safety Events, n (%)	Obefazimod 25 mg N=186	Obefazimod 50 mg N=447*
Any treatment-emergent adverse event (“TEAE”)	132 (71.0%)	307 (68.7%)
TEAE leading to study drug discontinuation	21 (11.3%)	27 (6.0%)
Serious TEAE	16 (8.6%)	23 (5.1%)
Death (Non-Treatment Related)⁽¹⁾	1 (0.5%)	0
Pregnancy⁽²⁾	1 (0.5%)	1 (0.2%)
Serious/severe (Grade ≥3) infections and opportunistic infections⁽³⁾	5 (2.7%)	5 (1.1%)
Malignancies (excluding NMSC)⁽⁴⁾	0	2 (0.4%)
NMSC⁽⁵⁾	2 (1.1%)	2 (0.4%)
Acute pancreatitis	1 (0.5%)	1 (0.2%)
Cardiac abnormalities suggestive of cardiac fibrosis	0	0

(1)	One death occurred in the 25 mg arm and was assessed by the investigator as unrelated to obefazimod. The suspected cause was pulmonary embolism in a 65+ patient with multiple pre-existing thromboembolic risk factors, including prior pulmonary embolism, and recent prolonged immobility.

(2)	Both pregnancies are currently ongoing.

(3)

Serious/severe (grade ≥3) infections and opportunistic infections: 25 mg = Appendicitis, Bartonellosis, Cytomegalovirus gastrointestinal infection, Peritonsillar abscess, Sepsis; 50 mg (induction non-responder) = Clostridium difficile infection, pilonidal disease, Urethritis gonococcal; 50 mg Open Label (Part 1 relapsers = Appendicitis (Part 1 50 mg), Septic arthritis staphylococcal (Part 1 placebo).

(4)	Part 1 relapsers previous on placebo: One case of Myoproliferative Neoplasm and one Prostate Cancer.

(5)	Two cases of Basal Cell Carcinoma (25 mg \| 50 mg) and two cases of Squamous Cell Carcinoma (25 mg \| 50 mg).

*	Includes combined induction non-responders on 50 mg in Part 2 (N=251) and Part 1 relapsers (N=196) who entered Part 2.

Malignancy

(Excluding

NMSC)

Exposure to
Obefazimod

Age

Thiopurine
History

Prior Advanced
Therapies

Other Prior UC
Treatment

Medical History
of Cancer

Summary

50 mg

Myeloproliferative Neoplasm (MPN)

7.4 months

40+

(adalimumab, infliximab)

mesalazine

Thrombocythemia since 2023.

Had elevated platelets at baseline (909,000 per microliter)

Determined not related to study drug by investigator

Prostate Cancer

3.4 months

55+

Yes

azathioprine

(infliximab, vedolizumab)

prednisolone, mesalazine, budesonide

Limited adenocarcinoma of the prostate CT2 CN0 M0; Gleason score 7B

Determined not related to study drug by investigator

S-3

NMSC

Exposure to
Obefazimod

Age

Thiopurine
History

Prior Advanced
Therapies

Other Prior UC
Treatment

Medical History
of Skin Cancer

Summary

50 mg

Basal Cell Carcinoma

10.4 months

40+

Yes

azathioprine

vedolizumab, infliximab, ustekinumab

mesalazine, prednisone

Thiopurine use and failure of 3 prior advanced therapies

Determined probably related to study drug by investigator

Squamous Cell Carcinoma

4.6 months

55+

Yes

azathioprine

adalimumab, vedolizumab

budesonide

Yes

Prior history of squamous cell carcinoma and history of multiple skin lesions

Determined not related to study drug by investigator

25 mg

Basal Cell Carcinoma

8.1 months

50+

Yes

azathioprine

None

budesonide, sulfasalazine, mesalazine, prednisone, metranidazole, sodium butyrate

Age 50+, prior thiopurine history

Determined unlikely related to study drug by investigator

Squamous Cell Carcinoma

8.3 months

75+

adalimumab, vedolizumab

prednisone, mesalamine

Yes

Age 75+ and prior history of 2x Basal
cell carcinoma

Determined probably related to study drug by investigator

The post-hoc analyses below are presented progressively, from the combined Phase 2 and Phase 3 UC programs to the Phase 3 maintenance dataset (Part 1 and Part 2), and then to the Part 2 maintenance dataset, to illustrate how increasing cumulative patient-years (“PYs”) strengthens our overall safety assessment. Because NMSCs and malignancies excluding NMSCs are uncommon events, incidence-rate estimates become more precise as cumulative exposure increases. We believe the Phase 3 maintenance data should be interpreted using the totality of the exposure-adjusted evidence, together with patient characteristics and representative published UC epidemiologic reference ranges. The results in the tables below demonstrate that the exposure-adjusted incidence rate (“EAIR”) in the combined all active (25 mg and 50 mg) treatment arms for both NMSCs and malignancies excluding NMSCs are within the UC background reference range based on published UC studies.

Malignancies (Excluding NMSC) – EAIR Analysis

Analysis Set

Placebo
IR/100 PY

25 mg
IR/100 PY

50 mg
IR/100 PY

All Active
IR/100 PY

Reference Range
Based on Published
UC Studies

Integrated UC Program
(Phase 2 + Phase 3)

0.00

0.64

0.35

0.30 – 0.70

Phase 3 Maintenance
(Part 1 + Part 2)

0.00

0.91

0.56

0.30 – 0.70

Part 2 Only

—

0.00

0.69

0.48

0.30 – 0.70

Note: IR = incidence rate

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NMSC – EAIR Analysis

Analysis Set

Placebo
IR/100 PY

25 mg
IR/100 PY

50 mg
IR/100 PY

All Active
IR/100 PY

Reference Range
Based on Published
UC Studies

Integrated UC Program
(Phase 2 + Phase 3)

0.46

0.53

0.64

0.59

0.70 – 1.40

Phase 3 Maintenance
(Part 1 + Part 2)

0.68

1.09

1.37

1.26

0.70 – 1.40

Part 2 Only

—

1.52

0.69

0.95

0.70 – 1.40

Note: IR = incidence rate

The overall safety results observed in Part 2 were consistent with those previously observed in the broader obefazimod clinical development program. No new safety pattern emerged with the additional cumulative exposure provided by Part 2.

Regulatory Path Forward

We believe the foregoing Part 2 results expand the integrated clinical dataset supporting the planned New Drug Application (“NDA”) for obefazimod in UC. We believe we remain on track to submit our NDA to the U.S. Food and Drug Administration in the fourth quarter of 2026.

Our Corporate Information

Our ADSs began trading on the Nasdaq Global Market in October 2023. We also maintain a website at www.abivax.com. The reference to our website is an inactive textual reference only and the information contained in, or that can be accessed through, our website or any other website cited in this prospectus supplement or the accompanying prospectus is not a part of this prospectus supplement or the accompanying prospectus.

Implications of Being an Emerging Growth Company

We qualify as an “emerging growth company” as defined in the JOBS Act. As an emerging growth company, we may take advantage of specified reduced disclosure and other requirements that are otherwise applicable generally to public companies. These provisions include:

•

exemption from the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act of 2002; and

•

to the extent that we no longer qualify as a foreign private issuer, (1) reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements and (2) exemptions from the requirements of holding a non-binding advisory vote on executive compensation, including golden parachute compensation.

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earliest to occur of: (i) the last day of the fiscal year in which our annual gross revenues exceed $1.235 billion; (ii) the first day of the year following the first year in which, as of the last business day of our most recently completed second fiscal quarter, the market value of our common equity held by non-affiliates exceeds $700 million; (iii) the date on which we have issued more than $1.0 billion in non-convertible debt securities during the previous three years; and (iv) the last day of the fiscal year ending after the fifth anniversary of our initial public offering of our ADSs.

We may choose to take advantage of some but not all of these exemptions. For example, Section 107 of the JOBS Act provides that an emerging growth company can use the extended transition period provided in Section 7(a)(2)(B) of the Securities Act for complying with new or revised accounting standards. Given that we currently report and expect to continue to report under IFRS, as issued by the IASB, we have irrevocably elected not to avail ourselves of this extended transition period, and, as a result, we will adopt new or revised accounting standards on the relevant dates on which adoption of such standards is required by the IASB. Since IFRS make no distinction between public and private companies for purposes of compliance with new or revised accounting standards, the requirements for our compliance as a private company and as a public company are the same.

Implications of Being a Foreign Private Issuer

We are also considered a “foreign private issuer” under U.S. securities laws. In our capacity as a foreign private issuer, we are exempt from certain rules under the Exchange Act that impose certain disclosure obligations and procedural requirements for proxy solicitations under Section 14 of the Exchange Act. In addition, our executive officers, members of our board of directors and our principal shareholders are exempt from “short-swing” profit recovery provisions of Section 16 of the Exchange Act and the rules under the Exchange Act with respect to their purchases and sales of our securities.

Moreover, we are not required to file periodic reports and financial statements with the SEC as frequently or as promptly as U.S. companies whose securities are registered under the Exchange Act. In addition, we are not required to comply with Regulation FD, which restricts the selective disclosure of material information.

We may take advantage of these exemptions until such time as we are no longer a foreign private issuer. We will remain a foreign private issuer until such time that more than 50% of our outstanding voting securities are held by U.S. residents and any of the following three circumstances applies: (1) the majority of our executive officers or directors are U.S. citizens or residents; (2) more than 50% of our assets are located in the United States; or (3) our business is administered principally in the United States.

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THE OFFERING

Offering

6,400,000 ADSs offered by us, each representing one ordinary share.

Option to Purchase Additional ADSs

The underwriters have an option, exercisable on or before the initial settlement date, to purchase up to an aggregate of 960,000 ADSs at the public offering price.

Ordinary Shares (Including in the Form of ADSs) to be Outstanding After this Offering

86,094,535 ordinary shares (including in the form of ADSs) or up to 87,054,535 ordinary shares (including in the form of ADSs) if we issue 960,000 additional ADSs pursuant to the exercise in full of the underwriters’ option.

American Depositary Shares

Purchasers of ADSs in the offering will have the rights of an ADS holder as provided in the deposit agreement among us, the depositary and all holders and beneficial owners of ADSs issued thereunder. To better understand the terms of the ADSs, you should carefully read the section in the accompanying prospectus titled “Description of American Depositary Shares.” We also encourage you to read the deposit agreement, which is filed as an exhibit to the registration statement that includes the accompanying prospectus.

Depositary

Citibank, N.A.

Use of Proceeds

We estimate that we will receive net proceeds from this offering of approximately $759.8 (€666.8) million based on the public offering price of $125.00 per ADS, after deducting underwriting discounts and commissions and estimated offering expenses payable by us, and assuming no issuance by us of additional ADSs pursuant to the exercise of the underwriters’ option to purchase up to 960,000 additional ADSs in this offering. If we issue 960,000 additional ADSs pursuant to the exercise in full of the underwriters’ option in the offering, we estimate that we will receive net proceeds from the offering of approximately $874.1 (€767.1) million.

We intend to use the net proceeds from this offering for expenses relating to potential commercialization of our lead drug candidate, obefazimod, in the United States; clinical research and development expenses, primarily related to ulcerative colitis and Crohn’s disease; and the remainder, if any, for general corporate purposes. We may also use a portion of the net proceeds to in-license, invest in or acquire businesses, technologies, products or assets that we believe are complementary to our own, although we have no current plans, commitments or agreements with respect to any such transactions as of the date of this prospectus supplement.

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The Nasdaq Global Market Symbol for our ADSs

“ABVX”

Regulated Market of Euronext in Paris Trading Symbol for our Ordinary Shares

“ABVX”

Settlement

We expect to deliver the ADSs on or about the date of delivery specified on the cover page of this prospectus supplement, which will be the second business day following the trade date for the ADSs (this settlement cycle being referred to as “T+2”). Under Rule 15c6-1 of the Exchange Act, trades in the secondary market generally are required to settle in one business day unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the ADSs prior to the business day preceding the date of delivery will be required, by virtue of the fact that the ADSs initially will settle in T+2, to specify an alternate settlement cycle at the time of any such trade to prevent a failed settlement and should consult their own advisors.

Risk Factors

Before deciding whether to invest in our ordinary shares (including in the form of ADSs), you should carefully consider the risks described under “Risk Factors” beginning on page S-9 of this prospectus supplement, as well as the other information included or incorporated by reference into this prospectus supplement and the accompanying prospectus, including our financial statements and the notes thereto.

Except as otherwise noted in this prospectus supplement, the number of ordinary shares (including in the form of ADSs) that will be outstanding after this offering is based on 79,694,535 ordinary shares outstanding as of March 31, 2026 (as adjusted to give effect to the issuance of 403,347 ADSs in the Royalty Certificate Repurchase), and excludes:

•

277,204 ordinary shares issuable upon the exercise of share warrants (BSA) outstanding as of March 31, 2026 at a weighted-average exercise price of €16.26 per ordinary share (or $18.70 based on the exchange rate in effect as of March 31, 2026);

•

205,139 ordinary shares issuable upon the exercise of founder’s share warrants (BCE) outstanding as of March 31, 2026 at a weighted-average exercise price of €10.20 per ordinary share (or $11.73 based on the exchange rate in effect as of March 31, 2026); and

•

8,083,287 ordinary shares issuable upon vesting of free shares (AGAs) outstanding as of March 31, 2026.

Except as otherwise noted, the information in this prospectus supplement assumes:

•

no exercise of the BSA and BCE or vesting of the AGAs listed above; and

•

no issuance by us of additional ADSs pursuant to the exercise of the underwriters’ option to purchase up to 960,000 additional ADSs in this offering.

S-8

RISK FACTORS

Investing in our ordinary shares (including ordinary shares in the form of ADSs) involves a high degree of risk. You should carefully consider the risks and uncertainties described below, as well as general economic and business risks, including those set forth in the section titled “Risk Factors” included in our Annual Report on Form 20-F for the year ended December 31, 2025 incorporated by reference herein, together with all of the other information in this prospectus supplement, the accompanying prospectus, and the documents incorporated by reference herein, including our consolidated financial statements and related notes, before deciding whether to purchase our securities. If any of the following risks are realized, our business, financial condition, operating results and prospects could be materially and adversely affected. In that event, the market price of our securities could decline, and you could lose part or all of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations. Please also read carefully the section above titled “Special Note Regarding Forward-Looking Statements.”

Risks Related to this Offering

Our management will have broad discretion over the use of the proceeds from this offering and may apply these proceeds in ways that may not increase the value of your investment.

Our management will have broad discretion to use the net proceeds we receive from this offering, and you will be relying on its judgment regarding the application of these proceeds. We may spend or invest these proceeds in a way with which our shareholders disagree. The failure by our management to apply these funds effectively could harm our business and financial condition. We expect to use the net proceeds from this offering as described under the heading “Use of Proceeds.” However, management may not apply such proceeds in ways that increase the value of your investment.

If you purchase ADSs in the offering, you will experience substantial and immediate dilution.

If you purchase ADSs in the offering, you will experience substantial and immediate dilution of $110.78 per ADS (€97.27 per ordinary share) in as adjusted net tangible book value after giving effect to the Royalty Certificate Repurchase and this offering at the public offering price of $125.00 per ADS in the offering, because the price that you pay will be substantially greater than the as adjusted net tangible book value per ADS that you acquire. This dilution is due in large part to the fact that our earlier investors paid substantially less than the public offering price when they purchased their ADSs or ordinary shares, as applicable. You will experience additional dilution at the end of the vesting period for our free shares that we have granted, and upon exercise of any outstanding share warrants to purchase ordinary shares, or if we otherwise issue additional ordinary shares or ADSs below the public offering price. For a further description of the dilution that you will experience immediately after the offering, see “Dilution.”

Concurrent or future sales of ordinary shares or ADSs by existing shareholders could depress the market price of the ADSs and ordinary shares.

We believe that additional capital will be needed to continue our planned operations, including conducting our planned clinical trials, manufacturing and commercialization efforts, expanded research and development activities and costs associated with operating as a public company. Additional financing may be obtained through additional equity offerings, which may include underwritten offerings, private placement financing or the initiation of an at-the-market program. Sales of additional ordinary shares or ADSs by us, or the perception that these sales could occur, could cause the market price of our ADSs to decline.

If existing shareholders sell, or indicate an intent to sell, substantial amounts of ordinary shares or ADSs in the public market after the 60-day contractual lock-up and other legal restrictions on resale discussed in this prospectus supplement lapse, the trading price of the ADSs and ordinary shares could decline significantly and could decline below the public offering price. Upon completion of this offering and based on the number of

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ordinary shares (including ordinary shares in the form of ADSs) outstanding as of March 31, 2026, after giving effect to the Royalty Certificate Repurchase, we will have outstanding 86,094,535 ordinary shares (including ordinary shares in the form of ADSs) assuming no issuance by us of additional ADSs pursuant to the exercise of the underwriters’ option, approximately 1,182,661 of which will be subject to a contractual restriction on selling for up to 60 days, subject to certain exceptions. The underwriters may permit our executive officers and directors to sell ADSs or ordinary shares prior to the expiration of the lock-up agreements. See “Underwriting.”

After the 60-day lock-up agreements with our executive officers and board members expire, additional ordinary shares (including in the form of ADSs) will be eligible for sale by such executive officers and board members in the public market, subject to compliance with applicable requirements under Rule 144 or Regulation S. In addition, the ordinary shares subject to outstanding warrants and outstanding free shares will become eligible for sale in the public market in the future, subject to certain legal and contractual limitations. We have filed a registration statement on Form S-8 with the SEC covering the ordinary shares issuable upon exercise of outstanding share warrants and vesting of outstanding free shares. Sales of a large number of ordinary shares or ADSs in the public market by our officers or board members or by significant shareholders upon the exercise of share warrants or vesting of free shares, in future public offerings by us or otherwise could have an adverse effect on the market price of the ADSs or ordinary shares. If these additional ordinary shares are sold, or if it is perceived that they will be sold, in the public market, the trading price of the ADSs and ordinary shares could decline substantially.

Raising additional capital, including as a result of this offering, may cause dilution to our shareholders, restrict our operations or require us to relinquish rights to our product candidates.

Until such time, if ever, as we can generate substantial revenue from the sale of our product candidates, we expect to finance our cash needs through a combination of equity offerings, debt financing, collaborations, strategic alliances and licensing arrangements. To the extent that we raise additional capital through the sale of equity securities, or convertible debt securities, your ownership interest will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect your rights as a shareholder. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends. If we raise additional funds through collaborations, strategic alliances or marketing, distribution or licensing arrangements with third parties, we may be required to relinquish valuable rights to our research programs or product candidates or grant licenses on terms that may not be favorable to us. If we are unable to raise additional funds through equity or debt financings or other arrangements with third parties when needed, we may be required to delay, limit, reduce or terminate our drug development or future commercialization efforts or grant rights to third parties to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

The biotechnology industry has been included in the list of critical technologies subject to foreign investment control procedure in France, which may limit the ability to certain non-French investors to participate in this or any other offering of our securities.

The completion of any investment (i) by (a) an individual of foreign nationality, (b) any individual of French nationality not domiciled in France within the meaning of Article 4B of the French General Tax Code (Code général des impôts), (c) any entity governed by foreign law, and (d) any entity governed by French law controlled by one or more of the individuals or entities referred to in (a) to (c), (ii) which would result in (a) the acquisition of control-within the meaning of Article L. 233-3 of the French Commercial Code (Code de commerce)-of a French company, (b) the acquisition of all or part of an activity of a French company, or (c) for individuals who are not nationals of a Member State of the European Union or of a State party to the agreement on the European Economic Area that has entered into an administrative assistance agreement with France and/or are not domiciled in one of these States, or for legal entities of which at least one of the members of the control chain is not governed by the law of one of these States or is not a national and/or is not domiciled there, to cross

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the threshold of 25% of the voting rights of a French company, or (d) for individuals who are not nationals of a Member State of the EU or of a State party to the agreement on the EEA that has entered into an administrative assistance agreement with France and/or are not domiciled in one of these State, or for legal entities of which at least one of the members of the control chain is not governed by the law of one of these States or is not a national and/or is not domiciled there, to cross the threshold of 10% of the voting rights of a French company whose shares are admitted to trading on a regulated market and (iii) whose activities concern, even occasionally, the research and development of so-called critical technologies, such as biotechnologies, and considered essential to the protection of public health, is subject to prior authorization by the French Minister of the Economy (ministère de l’Économie). The French Decree No. 2023-1293 of December 28, 2023 has made permanent the temporary regime under French Decree No. 2022-1622 of December 23, 2022, which expired on December 31, 2023.

The crossing of the threshold of 10% of the voting rights of French companies whose shares are admitted to trading on a regulated market is subject to a fast track review procedure (filing of a simplified form, delay for the Minister to respond limited to 10 business days, transaction deemed authorized in the absence of a response at the end of the delay).

If an investment in the Company requiring the prior authorization of the Minister of the Economy is made without such authorization having been granted, the Minister of the Economy may cancel the transaction or order (possibly under financial penalty) the investor concerned (i) to submit an application for authorization, (ii) to have the previous situation restored at its own expense or (iii) to modify the investment. In addition, the Minister may impose undertakings and conditions on the investor (including regular reporting commitments). The investor concerned could also be declared criminally liable and be sanctioned, in particular, by exclusion from any public contract or by a fine which may not exceed the highest of the following three amounts: (i) twice the amount of the investment concerned, (ii) 10% of our annual pre-tax revenues and (iii) €5 million (for a company) or €1 million (for an individual). The application of these regulations is likely to constitute a potential barrier to investments made by investors located outside the European Economic Area and could therefore limit our access to sources of financing.

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USE OF PROCEEDS

We believe that the net proceeds from the offering, together with our existing cash, cash equivalents and other short-term investments will be sufficient to meet our working capital requirements into the second quarter of 2029, assuming no exercise of the underwriters’ option to purchase additional ADSs. Our estimates of the period of time through which our financial resources are expected to be adequate to meet our working capital requirements are forward-looking statements and involve risks and uncertainties, and actual results could vary materially and negatively as a result of a number of factors, as described under “Special Note Regarding Forward-Looking Statements.”

This expected use of proceeds from the offering represents our intentions based upon our current plans and business conditions, which could change in the future as our plans and business conditions evolve. The amounts and timing of our actual expenditures may vary significantly depending on numerous factors, including the progress of our research and development efforts, the timing and success of preclinical studies, our ongoing clinical trials or clinical trials we may commence in the future, as well as any collaborations that we may enter into with third parties for our drug candidates, the timing of regulatory submissions and any unforeseen cash needs. As a result, our management retains broad discretion over the allocation of the net proceeds from the offering.

Pending our use of the net proceeds from the offering, we intend to invest the net proceeds in a variety of capital preservation investments, including short-term, investment-grade, interest-bearing instruments.

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CAPITALIZATION

The following table sets forth our cash, cash equivalents and other short-term investments and capitalization in euros and U.S. dollars as of March 31, 2026 on:

•

an actual basis;

•

an as adjusted basis to give effect to the Royalty Certificate Repurchase; and

•

a pro forma as adjusted basis to give further effect to the issuances of our ADSs in this offering (assuming no exercise of the option of the underwriters in this offering to purchase additional ADSs), after deducting the underwriting discounts and commissions and our estimated offering expenses.

The information in the table below is illustrative only, and our capitalization following the completion of this offering, if it is completed, will depend on the final terms of the offering.

The information set forth in the following table should be read in conjunction with and is qualified in its entirety by our financial statements and notes thereto incorporated by reference in this prospectus supplement and the accompanying prospectus.


	As of March 31, 2026
*(In thousands)*	Actual						As Adjusted						Pro Forma As Adjusted
	€			$⁽¹⁾			€			$⁽¹⁾			€			$⁽¹⁾
Cash, cash equivalents and other short-term investments(1)		477,423			548,941			438,286			503,941			1,105,109			1,263,720
Debt:
Financial liabilities – current portion		1,101			1,266			1,101			1,266			1,101			1,266
Financial liabilities – non-current portion		33,110			38,070			347			399			347			399
Total debt		34,211			39,336			1,448			1,665			1,448			1,665
Equity attributable to shareholders:
Ordinary shares(2)(3)		793			912			797			916			861			989
Premiums related to share capital		1,191,083			1,369,507			1,230,216			1,414,502			1,896,975			2,174,208
Translation reserves		2,029			2,333			2,029			2,333			2,029			2,333
Retained earnings		(715,843	)		(823,076	)		(715,843	)		(823,076	)		(715,843	)		(823,076	)
Net loss		(48,468	)		(55,729	)		(87,903	)		(101,071	)		(87,903	)		(101,071	)

Total shareholders’ equity		429,594			493,947			429,296			493,605			1,096,119			1,253,383

Total capitalization		463,805			533,283			430,744			495,269			1,097,567			1,255,048

(1)

Translated solely for convenience at an exchange rate of €1.00 = $1.1498, the exchange rate as reported by the European Central Bank on March 31, 2026, except for the net proceeds of the offering, which has been based on an exchange rate of €1.00 = $1.1394 on June 30, 2026. As adjusted and pro forma as adjusted cash, cash equivalents and other short-term investments reflect $45.0 million in cash payments related to the Royalty Certificate Repurchase.

(2)	On an actual basis, as of March 31, 2026, our outstanding share capital consisted of a total of 79,291,188 ordinary shares, with nominal value of €0.01 per share, all issued and outstanding.

(3)	The outstanding share information set forth above is as of March 31, 2026, and excludes, as of that date:

•

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•

8,083,287 ordinary shares issuable upon vesting of free shares (AGAs) outstanding as of March 31, 2026.

S-14

DILUTION

If you invest in our ADSs in this offering, your ownership interest will be diluted to the extent of the difference between the public offering price per ADS paid by you and our as adjusted net tangible book value (deficit) per ADS after completion of this offering.

Our net tangible book value as of March 31, 2026 was €404.6 million ($465.2 million), or €5.10 ($5.87) per ADS, based on an exchange rate of €1.00 = $1.1498, the exchange rate as reported by the European Central Bank on March 31, 2026. Net tangible book value per ADS is determined by dividing (1) our total assets less our intangible assets (including goodwill) and our total liabilities by (2) the number of ordinary shares outstanding as of March 31, 2026, or 79,291,188 ordinary shares. For the purposes of this “Dilution” section, we assume all outstanding ordinary shares are held in the form of ADSs for the purpose of per ADS calculations.

Our as adjusted net tangible book value as of March 31, 2026 was €404.3 million ($464.8 million), or €5.07 ($5.83) per ADS, based on an exchange rate of €1.00 = $1.1498, the exchange rate as reported by the European Central Bank on March 31, 2026. Our as adjusted net tangible book value per ADS is our net tangible book value as of March 31, 2026, after giving effect to the issuance of 403,347 ADSs in the Royalty Certificate Repurchase.

After giving effect to our sale of 6,400,000 ADSs in this offering, assuming all ADSs in the offering are sold at the public offering price of $125.00 per ADS, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma as adjusted net tangible book value as of March 31, 2026 would have been €1,071.1 ($1,224.6) million, or €12.44 ($14.22) per ADS. This represents an immediate increase in as adjusted net tangible book value of €7.37 ($8.39) per ADS to existing shareholders and an immediate dilution in as adjusted net tangible book value of €97.27 ($110.78) per ADS to new investors.

The following table illustrates this dilution on a per ADS basis:


	Per ADS
Public offering price				€	109.71				$	125.00
Historical net tangible book value per ADS as of March 31, 2026	€	5.10				$	5.87
Decrease in net tangible book value per ADS attributable to the Royalty Certificate Repurchase		(0.03	)				(0.03	)

As adjusted net tangible book value per ADS as of March 31, 2026		5.07					5.83
Increase in as adjusted net tangible book value per ADS attributable to new investors participating in this offering		7.37					8.39

Pro forma as adjusted net tangible book value per ADS as of March 31, 2026 after giving effect to this offering					12.44					14.22

Dilution per ADS to investors participating in this offering				€	97.27				$	110.78

If we issue 960,000 additional ADSs pursuant to the exercise in full of the underwriters’ option, the pro forma as adjusted net tangible book value after this offering would be €13.46 ($15.38) per ADS, the increase in the as adjusted net tangible book value to existing shareholders would be €8.38 ($9.55) per ADS, and the dilution to investors participating in this offering would be €96.25 ($109.62) per ADS.

In addition, we may choose to raise additional capital because of market conditions or strategic considerations, even if we believe that we have sufficient funds for our current or future operating plans. If we raise additional capital through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our securityholders. To the extent that we issue additional ordinary shares under

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our equity incentive plans, pursuant to draws under our existing equity line facility, through the establishment of an at-the-market program, or upon the exercise of share warrants, there will be further dilution to investors in this offering.

Except as otherwise noted in this prospectus supplement, the number of ordinary shares (including in the form of ADSs) that will be outstanding after this offering is based on 79,291,188 ordinary shares outstanding as of March 31, 2026, and excludes:

•

8,083,287 ordinary shares issuable upon vesting of free shares (AGAs) outstanding as of March 31, 2026.

Except as otherwise noted, the information in this prospectus supplement assumes:

•

no exercise of the BSA and BCE or vesting of the AGAs listed above; and

•

no issuance by us of additional ADSs pursuant to the exercise of the underwriters’ option to purchase additional ADSs in this offering.

S-16

TAXATION

Material U.S. Federal Income Tax Considerations

The following is a description of the material U.S. federal income tax consequences to the U.S. Holders described below of acquiring, owning and disposing of the ADSs acquired pursuant to this offering. It is not a comprehensive description of all tax considerations that may be relevant to a particular person’s decision to acquire securities. This discussion applies only to U.S. Holders that hold ADSs as “capital assets” (generally, property held for investment) under the U.S. Internal Revenue Code of 1986, as amended (the “Code”). In addition, it does not describe all of the tax considerations that may be relevant in light of a U.S. Holder’s particular circumstances, including U.S. federal estate and gift taxes, the Medicare contribution tax on net investment income, alternative minimum tax considerations, the special tax accounting rules under Section 451(b) of the Code, any state, local, or non-U.S. tax considerations, and tax considerations applicable to U.S. Holders subject to special rules, including, without limitation:

•

certain financial institutions;

•

traders in securities who use a mark-to-market method of tax accounting;

•

dealers in securities or currencies;

•

persons holding ADSs as part of a hedging transaction, “straddle,” wash sale, conversion transaction or integrated transaction or persons entering into a constructive sale with respect to the ADSs;

•

regulated investment companies;

•

insurance companies;

•

real estate investment trusts, grantor trusts or other trusts;

•

persons whose “functional currency” for U.S. federal income tax purposes is not the U.S. dollar;

•

expatriates of the United States;

•

tax exempt entities, including “individual retirement accounts” and “Roth IRAs”;

•

entities or arrangements classified as partnerships or other pass-through entities for U.S. federal income tax purposes (and investors therein);

•

persons that received ADSs as compensation for the performance of services;

•

persons that own or are deemed to own ten percent or more of our shares (by vote or value); and

•

persons holding ADSs in connection with a trade or business, permanent establishment, or fixed base outside the United States.

If an entity or arrangement that is classified as a partnership for U.S. federal income tax purposes holds the ADSs, the U.S. federal income tax treatment of a partner in that partnership will generally depend on the status of the partner and the activities of the partnership. Entities or arrangements treated as partnerships holding the ADSs and partners in such partnerships are encouraged to consult their own tax advisers as to the particular U.S. federal income tax consequences of acquiring, owning, and disposing of the ADSs.

This description is based on the Code, existing, proposed and temporary U.S. Treasury Regulations promulgated thereunder and administrative and judicial interpretations thereof, in each case as in effect and available on the date hereof. All of the foregoing is subject to change, which change could apply retroactively, and to differing interpretations, all of which could affect the tax considerations described below. No rulings have been sought from the U.S. Internal Revenue Service (the “IRS”) regarding the matters discussed herein and there can be no assurance that the IRS will not take a contrary position concerning the tax consequences of the acquisition, ownership and disposition of the ADSs or that such a position will not be sustained. U.S. Holders should consult their own tax advisers concerning the U.S. federal, state, local and non-U.S. tax consequences of acquiring, owning, and disposing of the ADSs in their particular circumstances.

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As used for purposes of this section “—Material U.S. Federal Income Tax Considerations,” a “U.S. Holder” is a holder who, for U.S. federal income tax purposes, is a beneficial owner of the ADSs that is an initial purchaser of the ADSs sold in this offering of our ADSs in the United States and is:

•

an individual who is a citizen or resident of the United States;

•

a corporation, or other entity taxable as a corporation, created or organized in or under the laws of the United States, any state therein or the District of Columbia;

•

an estate whose income is eligible for inclusion in gross income for U.S. federal income tax purposes, regardless of its source; or

•

a trust, if (A) a U.S. court is able to exercise primary supervision over the trust’s administration and one or more United States persons (as such term is defined under the Code) have authority to control all substantial decisions of the trust, or (B) the trust has a valid election in place under applicable U.S. Treasury Regulations to treat the trust as a United States person.

The discussion below assumes that the representations contained in the depositary agreement are true and that the obligations in the depositary agreement and any related agreement will be complied with in accordance with its terms. For U.S. federal income tax purposes, it is generally expected that a U.S. Holder of ADSs will be treated as the beneficial owner of the underlying ordinary shares represented by the ADSs. The remainder of this discussion assumes that a U.S. Holder of our ADSs will be treated in this manner. Accordingly, deposits or withdrawals of ADSs for ordinary shares will generally not be subject to U.S. federal income tax.

U.S. Holders are encouraged to consult their own tax advisers concerning the U.S. federal, state, local and foreign tax consequences of acquiring, owning and disposing of the ADSs in their particular circumstances.

Taxation of Distributions

Subject to the passive foreign investment company (“PFIC”) rules described below, distributions paid on the ADSs, other than certain pro rata distributions of the ADSs, will generally be treated as dividends to the extent paid out of our current or accumulated earnings and profits (as determined under U.S. federal income tax principles). We do not maintain calculations of our earnings and profits under U.S. federal income tax principles, and so we expect that distributions generally will be reported to U.S. Holders as dividends. Subject to applicable limitations, dividends paid by a “qualified foreign corporation” are eligible for taxation at a preferential capital gains rate rather than the marginal tax rates generally applicable to ordinary income provided that certain requirements are met. However, if we are a PFIC (or treated as a PFIC with respect to the U.S. Holder) for the taxable year in which the dividend is paid or the preceding taxable year (see discussion below under “Passive Foreign Investment Company Rules”), we will not be treated as a qualified foreign corporation, and therefore the preferential capital gains tax rate described above will not apply. Each U.S. Holder is advised to consult its tax advisors regarding the availability of the preferential tax rate on dividends with regard to its particular circumstances.

A non-U.S. corporation (other than a corporation classified as a PFIC for the taxable year in which the dividend is paid or the preceding taxable year) generally will be considered to be a qualified foreign corporation: (i) if it is eligible for the benefits of a comprehensive tax treaty with the United States, which the Secretary of Treasury of the United States determines is satisfactory for purposes of this provision, and which includes an exchange of information provision; or (ii) with respect to any dividend it pays on shares that are readily tradable on an established securities market in the United States. We believe that we qualify as a resident of France for the purposes of, and are eligible for the benefits of, the income tax treaty between France and the United States, which the IRS has determined is satisfactory for purposes of the qualified dividend rules, and that it includes an exchange of information provision, although there can be no assurance in this regard. Further, our ADSs will generally be considered to be readily tradable on an established securities market in the United States, including the Nasdaq Global Market. Therefore, subject to the discussion below under “Passive Foreign Investment

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Company Rules,” if the income tax treaty between France and the United States is applicable, or if the ADSs are readily tradable on an established securities market in the United States, dividends paid on the ADSs will generally be “qualified dividend income” subject to lower applicable long-term capital gain rate in the hands of certain non-corporate U.S. Holders including individuals, provided that certain conditions are met, including conditions relating to the holding period and the absence of certain risk reduction transactions.

A U.S. Holder must include the gross amount of a dividend without reduction for amounts withheld by us in respect of French income taxes (see “—Material French Income Tax Considerations”), even though the U.S. Holder did not in fact receive the amount associated with the withheld French tax. The amount of the dividend will be treated as foreign-source dividend income to U.S. Holders and will not be eligible for the dividends-received deduction generally available to U.S. corporations under the Code. Dividends generally will be included in a U.S. Holder’s income on the date of the U.S. Holder’s receipt (or deemed receipt) of the dividend. The amount of any distribution of property other than cash (excluding certain pro rata distributions of ADSs or rights to acquire ADSs) will be the fair market value of such property on the date of the distribution. The amount of any dividend income paid in euros will be the U.S. dollar amount calculated by reference to the exchange rate in effect on the date of actual or constructive receipt, regardless of whether the payment is in fact converted into U.S. dollars. If the dividend is converted into U.S. dollars on the date of receipt, a U.S. Holder should not be required to recognize foreign currency gain or loss in respect of the dividend income. A U.S. Holder may have foreign currency gain or loss if the dividend is converted into U.S. dollars after the date of receipt.

Subject to applicable limitations, some of which vary depending upon the U.S. Holder’s particular circumstances, French income taxes withheld from dividends on the ADSs at a rate not exceeding the rate provided by the income tax treaty between France and the United States generally will be creditable against the U.S. Holder’s U.S. federal income tax liability. Dividend distributions with respect to the ADSs generally will be treated as “passive category” income from sources outside the United States for purposes of determining a U.S. Holder’s U.S. foreign tax credit limitation. The rules governing foreign tax credits are complex and U.S. Holders should consult their tax advisers regarding the creditability of foreign taxes in their particular circumstances. In lieu of claiming a foreign tax credit, U.S. Holders may, at their election, deduct foreign taxes, including any French income tax, in computing their taxable income, subject to generally applicable limitations under U.S. law. An election to deduct foreign taxes instead of claiming foreign tax credits applies to all foreign taxes paid or accrued in the taxable year.

Sale or Other Taxable Disposition of the ADSs

Subject to the PFIC rules described below, a U.S. Holder generally will recognize gain or loss for U.S. federal income tax purposes upon the sale, exchange or other taxable disposition of the ADSs in an amount equal to the difference between the U.S. dollar value of the amount realized from such sale or exchange and the U.S. Holder’s tax basis for those ADSs. Subject to the PFIC rules described below, this gain or loss generally will be a capital gain or loss. The tax basis in an ADS generally will be equal to the cost of such ADS. Capital gain from the sale, exchange or other taxable disposition of ADSs of a non-corporate U.S. Holder is generally eligible for a preferential rate of taxation applicable to capital gains, if the non-corporate U.S. Holder’s holding period determined at the time of such sale, exchange or other taxable disposition for such ADSs exceeds one year (i.e., such gain is long-term taxable gain). The deductibility of capital losses is subject to limitations for U.S. federal income tax purposes. Any such gain or loss that a U.S. Holder recognizes generally will be treated as U.S. source income or loss for foreign tax credit limitation purposes.

For a cash basis taxpayer, units of foreign currency paid or received are translated into U.S. dollars at the spot rate on the settlement date of the purchase or sale. In that case, no foreign currency exchange gain or loss will result from currency fluctuations between the trade date and the settlement date of such a purchase or sale. An accrual basis taxpayer, however, may elect the same treatment required of cash basis taxpayers with respect to purchases and sales of the ADSs that are traded on an established securities market, provided the election is applied consistently from year to year. Such election may not be changed without the consent of the IRS. For an accrual basis taxpayer who does not make such an election, units of foreign currency paid or received are

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translated into U.S. dollars at the spot rate on the trade date of the purchase or sale. Such an accrual basis taxpayer may recognize exchange gain or loss based on currency fluctuations between the trade date and the settlement date. Any foreign currency gain or loss a U.S. Holder realizes will be U.S. source ordinary income or loss.

Passive Foreign Investment Company Rules

Under the Code, we will be a PFIC for any taxable year in which, after the application of certain “look-through” rules with respect to subsidiaries, either (i) 75% or more of our gross income consists of “passive income,” or (ii) 50% or more of the average quarterly value of our assets (generally determined on the basis of a weighted quarterly average) consist of assets that produce, or are held for the production of, “passive income.” Passive income generally includes dividends, interest, gains from the sale or exchange of investment property and rents or royalties other than rents or royalties which are received from unrelated parties in connection with the active conduct of a trade or business. Passive assets include, among others, cash and assets readily convertible into cash, while our goodwill and other unbooked intangibles associated with active business activities may generally be treated as non-passive assets. In addition, for purposes of the above calculations, a non-U.S. corporation that owns, directly or indirectly, at least 25% by value of the equity interests of another corporation is treated as if it held its proportionate share of the assets of the other corporation, and received directly its proportionate share of the income of the other corporation. If a corporation is treated as a PFIC with respect to a U.S. Holder for any taxable year, the corporation will continue to be treated as a PFIC with respect to that U.S. Holder in all succeeding taxable years during which the U.S. Holder holds the ADSs, regardless of whether the corporation continues to meet the PFIC requirements in such years, unless certain elections are made.

Based on our analysis of our financial statements, activities and relevant market and shareholder data, we do not believe that we were a PFIC for the taxable year ended December 31, 2025. The determination of whether we are a PFIC is a fact-intensive determination made on an annual basis and the applicable law is subject to varying interpretation. Whether we are a PFIC for any taxable year will depend on the composition of our income and the composition, nature and value of our assets from time to time (including the value of our goodwill, which may be determined by reference to the value of our ADSs, which could fluctuate considerably). We currently do not generate product revenues and therefore we may be a PFIC for any taxable year in which we do not generate sufficient amounts of other non-passive income. As a result, there can be no assurance that we will not be treated as a PFIC for the current or any future taxable year and our U.S. counsel expresses no opinion with respect to our PFIC status for any prior, current or future taxable year. Even if we determine that we are not a PFIC for a taxable year, there can be no assurance that the IRS will agree with our conclusion or that the IRS will not successfully challenge our position.

If we are a PFIC for any taxable year during which a U.S. Holder holds the ADSs, the U.S. Holder may be subject to adverse tax consequences, regardless of whether we remain a PFIC. Generally, gain recognized upon a disposition (including, under certain circumstances, a pledge) of the ADSs by the U.S. Holder would be allocated ratably over the U.S. Holder’s holding period for such ADSs. The amounts allocated to the taxable year of disposition and to years before we became a PFIC would be taxed as ordinary income. The amount allocated to each other taxable year would be subject to tax at the highest rate in effect for that taxable year for individuals or corporations, as appropriate, and would be subject to an interest charge on the resulting tax deemed deferred with respect to each such other taxable year. Further, to the extent that any distribution received by a U.S. Holder on its ADSs exceeds 125% of the average of the annual distributions on such ADSs received by the U.S. Holder during the (i) preceding three years or (ii) the U.S. Holder’s holding period, whichever is shorter, that distribution would be subject to taxation in the same manner described immediately above with respect to gain on disposition.

Alternatively, if we are a PFIC and if the ADSs are “regularly traded” on a “qualified exchange,” a U.S. Holder could make a mark-to-market election that would result in tax treatment different from the general tax treatment described in the preceding paragraph. The ADSs would be treated as “regularly traded” in any calendar

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year in which more than a de minimis quantity of the ADSs are traded on a qualified exchange, including the Nasdaq Global Market, on at least 15 days during each calendar quarter. The ADSs are listed on the Nasdaq Global Market, and we expect, although no assurance can be given, that they will be regularly traded on the Nasdaq Global Market. U.S. Holders should consult with their own tax advisors regarding potential availability of the mark-to-market election.

If a U.S. Holder makes the mark-to-market election, the U.S. Holder generally will recognize as ordinary income any excess of the fair market value of the ADSs at the end of each taxable year over their adjusted tax basis, and will recognize an ordinary loss in respect of any excess of the adjusted tax basis of the ADSs over their fair market value at the end of the taxable year (but only to the extent of the net amount of income previously included as a result of the mark-to-market election). If a U.S. Holder makes the election, the U.S. Holder’s tax basis in the ADSs will be adjusted to reflect these income or loss amounts. Any gain recognized on the sale or other disposition of ADSs in a year when we are a PFIC will be treated as ordinary income and any loss will be treated as an ordinary loss (but only to the extent of the net amount of income previously included as a result of the mark-to-market election). If a U.S. Holder makes a mark-to-market election in respect of a corporation classified as a PFIC and such corporation ceases to be classified as a PFIC, the holder will not be required to take into account the gain or loss described above during any period that such corporation is not classified as a PFIC.

A timely election to treat a PFIC as a qualified electing fund under Section 1295 of the Code (“QEF Election”) would result in alternative treatment. If a U.S. Holder makes a QEF Election for the first tax year of such U.S. Holder’s holding period in which we are classified as a PFIC, then such U.S. Holder generally would not be subject to the PFIC rules described above. Instead, a U.S. Holder that makes a timely and effective QEF Election will currently include in gross income such U.S. Holder’s (i) pro rata share of our ordinary earnings as ordinary income and (ii) pro rata share of our net capital gain as long-term capital gain, regardless of whether we have made any distributions of such earnings or gain. The U.S. Holder’s basis in its ADSs would be increased to reflect the amount of such income inclusions. Generally, for this purpose, “ordinary earnings” are the excess of our (a) “earnings and profits” over (b) net capital gain, and “net capital gain” is the excess of our (a) net long-term capital gain over (b) net short-term capital loss.

A U.S. Holder that has made such a timely and effective QEF Election generally may receive a distribution tax-free as a return of capital to the extent that such distribution represents “earnings and profits” that were previously included in income by the U.S. Holder because of such QEF Election and such distribution will reduce such U.S. holder’s adjusted tax basis in our ADSs to reflect the amount allowed as a tax-free distribution because of such QEF Election. A U.S. Holder that makes a QEF Election would generally recognize capital gain or loss on the sale, exchange or other taxable disposition of its ADSs.

However, a U.S. Holder will only be able to make a QEF Election if we provide such U.S. Holder with certain tax information annually, and we may determine not to provide such information. Furthermore, if the IRS determines that we were a PFIC for a year with respect to which we had determined that we were not (or believed we were not) a PFIC, it might be too late for a U.S. Holder to make a timely QEF Election, unless the U.S. Holder qualifies under applicable U.S. Treasury Regulations to make a retroactive (late) election. U.S. Holders should consult their own tax advisors regarding the making of any such QEF Election.

In addition, if we are a PFIC or, with respect to particular U.S. Holders, are treated as a PFIC for the taxable year in which we paid a dividend or for the prior taxable year, the preferential rates discussed above with respect to dividends paid to certain non-corporate U.S. Holders would not apply.

If a U.S. Holder owns ADSs during any year in which we are a PFIC, the holder generally must file an IRS Form 8621, or such other form as is required by the U.S. Treasury Department, generally with the holder’s federal income tax return for that year.

U.S. Holders should consult their tax advisers regarding whether we are or may become a PFIC and the potential application of the PFIC rules.

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Information Reporting and Backup Withholding

Payments of distributions and sales proceeds that are made within the United States or through certain U.S.-related financial intermediaries generally are subject to information reporting, and may be subject to backup withholding, unless (i) the U.S. Holder is a corporation or other exempt recipient or (ii) in the case of backup withholding, the U.S. Holder provides a correct taxpayer identification number and certifies that it is not subject to backup withholding.

Backup withholding is not an additional tax. The amount of any backup withholding from a payment to a U.S. Holder will be allowed as a credit against the holder’s U.S. federal income tax liability and may entitle it to a refund, provided that the required information is timely furnished to the IRS.

Information With Respect to Foreign Financial Assets

Certain U.S. Holders who are individuals may be required to report information relating to their ownership of an interest in certain foreign financial assets, including stock of a non-U.S. person, generally on an IRS Form 8938, subject to exceptions (including an exception for stock held through a U.S. financial institution). In addition, certain U.S. Holders may be required to file a FinCEN Form 114 (Report of Foreign Bank and Financial Accounts) with the U.S. Treasury Department each year to report their interest in the ADSs. U.S. Holders should consult their tax advisers regarding their reporting obligations with respect to the ADSs.

Material French Income Tax Considerations

The following describes the material French income tax consequences to U.S. Holders (as defined below for the purposes of this section) of purchasing, owning and disposing of the ADSs and, unless otherwise noted, this discussion is the opinion of Orrick, our French tax counsel, insofar as it relates to matters of French tax law and legal conclusions with respect to those matters.

This discussion does not purport to be a complete analysis or listing of all potential tax effects of the acquisition, ownership or disposition of our ADSs to any particular investor, and does not discuss tax considerations that arise from rules of general application or that are generally assumed to be known by investors.

All of the following is subject to change. Such changes could apply retroactively and could affect the consequences described below.

The description of the French income tax and real estate wealth tax consequences set forth below is based on the Convention between the Government of the United States of America and the Government of the French Republic for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income and Capital of August 31, 1994 which came into force on December 30, 1995 (as amended by any subsequent protocols, including the protocol of January 13, 2009), and the tax guidelines issued by the French tax authorities in force as of the date hereof (the “Treaty”).

For the purposes of this discussion of French income tax consequences, the term “U.S. Holder” is a holder who, for U.S. federal income tax purposes, is a beneficial owner of the ADSs that is an initial purchaser of the ADSs sold in this offering of our ADSs in the United States and is: (i) an individual who is a citizen or resident of the United States, (ii) a corporation or other entity taxable as a corporation, created or organized in or under the laws of the United States, any state therein or the District of Columbia, (iii) an estate whose income is eligible for inclusion in gross income for U.S. federal income tax purposes, regardless of its source, or (iv) a trust, if (a) a U.S. court is able to exercise primary supervision over the trust’s administration and one or more U.S. persons have the authority to control all substantial decisions of the trust or (b) the trust has a valid election in effect under applicable U.S. Treasury Regulations to treat the trust as a United States person.

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If a partnership (or any other entity treated as partnership for U.S. federal income tax purposes) holds ADSs, the tax treatment of the partnership and a partner in such partnership generally will depend upon the status of the partner and the activities of the partnership. If a U.S. Holder is a partnership or a partner in a partnership that holds ADSs, such holder is urged to consult its own tax adviser regarding the specific tax consequences of acquiring, owning and disposing of securities.

This discussion applies only to investors that hold our ADSs as capital assets that have the U.S. dollar as their functional currency, that are entitled to Treaty benefits under the “Limitation on Benefits” provision contained in the Treaty, and whose ownership of the ADSs is not effectively connected to a permanent establishment or a fixed base in France.

Certain U.S. Holders (including, but not limited to, U.S. expatriates, partnerships or other entities classified as partnerships for U.S. federal income tax purposes, banks, insurance companies, regulated investment companies, tax-exempt organizations, financial institutions, persons subject to the alternative minimum tax, persons who acquired the securities pursuant to the exercise of employee share warrants or otherwise as compensation, persons that own (directly, indirectly or by attribution) 5% or more of our voting stock or 5% or more of our outstanding share capital, dealers in securities or currencies, persons that elect to mark their securities to market for U.S. federal income tax purposes and persons holding securities as a position in a synthetic security, straddle or conversion transaction) may be subject to special rules not discussed below.

U.S. Holders are urged to consult their own tax advisors regarding the tax consequences of the purchase, ownership and disposition of securities in light of their particular circumstances, especially with regard to the “Limitations on Benefits” provision.

Assets held through a Trust

France introduced a comprehensive set of tax rules applicable to French assets that are held by or in foreign trusts. These rules, among other things, provide for the inclusion of trust assets in the settlor’s net assets for purpose of applying the French real estate wealth tax for the application of French gift and inheritance duties to French assets held in trust, for a specific tax on capital on the French assets of foreign trusts not already subject to the French real estate wealth tax and for a number of French tax reporting and disclosure obligations. The following discussion does not address the French tax consequences applicable to ADSs held in trusts. If ADSs are held in trust, the settlor, trustee and beneficiary are urged to consult their own tax adviser regarding the specific tax consequences of acquiring, owning and disposing of ADSs through a trust.

Estate and Gift Taxes

In general, a transfer of securities by gift or by reason of death of a U.S. Holder that would otherwise be subject to French gift or inheritance tax, respectively, will not be subject to such French tax based on the Convention between the Government of the United States of America and the Government of the French Republic for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Estates, Inheritances and Gifts, dated November 24, 1978 (as amended by the protocol dated from December 8, 2004), unless the donor or the transferor is domiciled in France at the time of making the gift or at the time of his or her death, or the securities were used in, or held for use in, the conduct of a business through a permanent establishment or a fixed base in France.

Financial Transactions Tax

Under Article 235 ter ZD of the French Tax Code (“FTC”) (Code général des impôts), a financial transaction tax (“FTT”) (taxe sur les transactions financières) applies, subject to certain conditions and exemptions, to certain acquisitions of equity securities or equivalent instruments of French companies, including ordinary shares (which may be in the form of ADSs), whose market capitalization exceeds €1 billion as of December 1^st of the year preceding the year during which the taxable acquisition takes place, and whose shares

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are admitted to trading on a regulated market within the European Union, the European Economic Area or a foreign regulated market formally recognized as such by the Autorité des Marchés Financiers (“AMF”) (in each case within the meaning of the French Monetary and Financial Code, or the “FMFC”). The tax is currently levied at a rate of 0.4% of the acquisition price of the shares.

A list of French relevant companies whose market capitalization exceeds €1 billion as of December 1^st of the year preceding the taxation year is published annually by the French tax authorities. The last version of such list was dated December 17, 2025 (BOI-ANNX-000467). It included Abivax SA as its market capitalization exceeded €1.0 billion.

In addition, according to the French tax authorities’ guidelines, depositary receipts (including ADSs) representing shares issued by a French company are within the scope of the FTT where the underlying shares are admitted to trading on a regulated or recognized market, irrespective of the place where such depositary receipts are issued or traded. Although the Nasdaq Global Market, on which the ADSs are listed, is not currently recognized by the AMF, the ordinary shares represented by the ADSs are themselves admitted to trading on Euronext Paris, which is a recognized regulated market.

Accordingly, acquisitions for consideration of ADSs representing ordinary shares of Abivax should in principle fall within the scope of the FTT, subject to the application of any available exemptions, including notably the primary market transaction exemption.

It is being further noted that concerning ADSs creation, the French tax authorities’ guidelines provide that the acquisition of a share falling within the scope of the French FTT and the subsequent creation and acquisition of an ADSs representing this share, constitute a single transaction, which is subject to French FTT. The French FTT is payable, subject to any applicable exceptions, only when the ADS is acquired.

If the ADS is created not through the acquisition of an existing share but through the issue of a new share, the acquisition of the ADS could benefit from the primary market exemption.

Registration Duties

Acquisition of equity or similar securities subject to the abovementioned FTT are exempt from registration taxes provided for by Article 726 of the FTC.

In the case where the FTT is not applicable, (1) transfers of shares issued by a French company which are listed on a regulated or organized market within the meaning of the FMFC are subject to uncapped registration duties at the rate of 0.1% if the transfer is evidenced by a written statement (“acte”) executed either in France or outside France, whereas (2) transfers of shares issued by a French company which are not listed on a regulated or organized market within the meaning of the FMFC are subject to uncapped registration duties at the rate of 0.1% notwithstanding the existence of a written statement.

As our ordinary shares are listed on Euronext Paris, which is a regulated market within the meaning of the FMFC, their transfer should be subject to uncapped registration duties at the rate of 0.1% only if such transfer is evidenced by a written agreement.

Although French tax law and the official guidelines published by the French tax authorities are silent regarding the treatment of ADS representing listed shares of a French issuer for registration duties purposes (BOI-ENR-DMTOM-40-10-10-24/04/2024), ADSs should remain outside of the scope of the aforementioned 0.1% registration duties if the transfer is not evidenced by a written agreement. Furthermore, if the transactions in ADSs do not imply a transfer of ownership of the underlying shares they should be outside the scope of the registration duties. In case the transactions in the ADSs imply such a transfer, the 0.1% duty should not apply if the transfer is not evidenced by a written agreement.

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Real Estate Wealth Tax

Since January 1, 2018, the French wealth tax (impôt de solidarité sur la fortune) has been repealed and replaced by the French real estate wealth tax (impôt sur la fortune immobilière). The scope of the French real estate wealth tax is narrowed to real estate assets (and certain assets deemed to be real estate assets) or rights, held directly or indirectly through one or more legal entities and whose net taxable assets amount at least to €1,300,000.

Broadly, subject to provisions of double tax treaties and to certain exceptions, individuals who are not residents of France for tax purposes within the meaning of Article 4 B of the FTC, are subject to real estate wealth tax in France in respect of the portion of the value of their shares of our Company representing real estate assets (Article 965, 2° of the FTC). Some exceptions are provided by the FTC. For instance, any participations representing less than 10% of the share capital of an operating company and shares representing real estate for the professional use of the company considered shall not fall within the scope of the French real estate wealth tax. Under the Treaty (the provisions of which should be applicable to the real estate wealth tax in France), the French real estate wealth tax will however generally not apply to securities held by an eligible U.S. Holder who is a U.S. resident, as defined above and pursuant to the provisions of the Treaty, provided that such (i) U.S. Holder (a) does not own directly or indirectly more than 25% of the issuer’s financial rights and (b) that the ADSs do not form part of the business property of a permanent establishment or fixed base in France and (ii) that the issuer’s assets do not consist in at least 50 percent of real property located in France, or that the issuer’s shares do not derive at least 50 percent of their value, directly or indirectly, from real property located in France.

U.S. Holders are advised to consult their own tax advisor regarding the specific tax consequences which may apply to their particular situation with respect to such French real estate wealth tax.

Taxation of Dividends

Dividends paid by a French corporation, when their beneficial owners are not French tax residents are generally subject to French withholding tax at a rate of currently (i) 25% for dividends the beneficial owners of which are legal persons which are not French tax residents, and (ii) 12.8% for dividends the beneficial owners of which are individuals who are not French tax residents. Dividends paid by a French corporation in a non-cooperative State or territory, as defined in Article 238-0 A of the FTC, other than those states or territories mentioned in 2° of 2 bis of the same Article, will generally be subject to French withholding tax at a rate of 75% (unless the safeguard clause provided for by Article 187, 2 of the FTC were to apply).

However, eligible U.S. Holders entitled to Treaty benefits under the “Limitation on Benefits” provision contained in the Treaty who are U.S. residents, as defined pursuant to the provisions of the Treaty, may not be subject to this 12.8%, 25% or 75% withholding tax rate, but may be subject to the withholding tax at a reduced rate (as described below).

Under the Treaty, the rate of French withholding tax on dividends paid to an eligible U.S. Holder who is a U.S. resident as defined pursuant to the provisions of the Treaty and the beneficial owner of these dividends, whose ownership of the ordinary shares (which may be in the form of ADSs) is not effectively connected with a permanent establishment or fixed base that such U.S. Holder has in France, is generally reduced to 15%, or to 5% if such U.S. Holder is a corporation and owns directly or indirectly at least 10% of the share capital of the issuer; such U.S. Holder may under certain conditions claim a refund from the French tax authorities of the amount withheld in excess of the Treaty rates of 15% or 5%, if any.

For U.S. Holders that are not individuals but are U.S. residents, as defined pursuant to the provisions of the Treaty, the requirements for eligibility for Treaty benefits, including the reduced 5% or 15% withholding tax rates contained in the “Limitation on Benefits” provision of the Treaty, are complex, and certain technical changes were made to these requirements by the protocol of January 13, 2009. U.S. Holders are advised to consult their own tax advisers regarding their eligibility for Treaty benefits in light of their own particular circumstances.

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Dividends paid to an eligible U.S. Holder may immediately be subject to the reduced rates of 5% or 15% provided that:

•

such U.S. Holder establishes before the date of payment that it is a U.S. resident under the Treaty by completing and providing the depositary with a treaty form (Form 5000) in accordance with French guidelines (BOI-INT-DG-20-20-20-20-12/09/2012); or

•

the depositary or other financial institution managing the securities account in the United States of such U.S. Holder provides the French paying agent, with a document listing certain information about the U.S. Holder and its ordinary shares or ADSs and a certificate (BOI-LETTRE-000138-28/07/2014) whereby the financial institution managing the U.S. Holder’s securities account in the United States takes full responsibility for the accuracy of the information provided in the document.

Otherwise, dividends paid to a U.S. Holder, if such U.S. Holder is a legal person, will be subject to French withholding tax at the rate of 25%, or 75% if paid to an account situated in a non-cooperative State or territory (as defined in Article 238-0 A of the FTC, but other than those states or territories mentioned in 2° of 2 bis of the same Article 238-0 A of the FTC, unless the safeguard clause provided for by Article 187, 2 of the FTC were to apply), and then reduced at a later date to 5% or 15%, provided that such holder duly completes and provides the French tax authorities with the treaty forms Form 5000 and Form 5001 before December 31 of the year following the year during which the dividend is paid (due to recent case law regarding the statute of limitation for filing a withholding tax claim: U.S. Holders are advised to consult their own tax advisor in this respect).

Certain qualifying pension funds and certain other tax-exempt entities are subject to the same general filing requirements as other U.S. Holders except that they may have to supply additional documentation evidencing their entitlement to these benefits.

Since the withholding tax rate applicable under French domestic law to U.S. Holders who are individuals does not exceed the cap provided in the Treaty (i.e., 15%), the 12.8% rate shall apply, without any reduction provided under the Treaty.

Besides, please note that pursuant to Article 235 quater of the FTC and under certain conditions, a corporate U.S. Holder which is in a tax loss position for the fiscal year during which the dividend is received may be entitled to a deferral regime, and obtain a withholding tax refund. The tax deferral ends in respect of the first financial year during which this U.S. Holder is in a profit-making position, as well as in the cases set out in Article 235 quater of the FTC. Finance Bill for 2022 extended the deadline to claim the refund (December 31 of the second year following the year of payment instead of three months after the end of the fiscal year following the payment of the income) and clarified the order in which the deferred taxes become due (the forfeiture of the deferral applies in priority to the oldest withholding taxes). Also, pursuant to Article 235 quinquies of the FTC and under certain conditions, a corporate U.S. Holder may be entitled to a refund of a fraction of the withholding tax, up to the difference between the withholding tax paid (on a gross basis) and the withholding tax based on the dividend net of the expenses incurred for the acquisition and conservation directly related to the income, provided (i) that these expenses would have been tax deductible had the U.S. Holder been established in France, and (ii) that the tax rules in the United States do not allow the U.S. Holder to offset the withholding tax.

Tax on Sale or Other Disposition

As a matter of principle, under French tax law, and provided that Abivax SA is not a real estate company within the meaning of Article 244 bis A of the FTC, a U.S. Holder should not be subject to any French tax on any capital gain from the sale, exchange, repurchase or redemption by us of ADSs, provided such U.S. Holder is not a French tax resident for French tax purposes and has not held more than 25% of our dividend rights, known as “droits aux bénéfices sociaux” at any time during the preceding five years, either directly or indirectly, and, as relates to individuals, alone or with relatives. In the case of redemptions, all or part of the proceeds may, under certain circumstances, be partially or fully qualified as dividends for French domestic tax purposes and therefore be subject to French dividend withholding tax subject to the application of the Treaty.

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As an exception, a U.S. Holder resident, domiciled, established or incorporated in a non-cooperative State or territory as set out in the list referred to in Article 238-0 A of the FTC other than those mentioned in 2° of 2 bis of the same Article should be subject to a 75% withholding tax in France on any such capital gain, regardless of the fraction of the dividend rights it holds, unless the safeguard clause provided by the second paragraph of Article 244 bis B of the FTC were to apply. This list of non-cooperative States or territories was last updated on April 15, 2026, and currently includes Anguilla, Antigua and Barbuda, Guam, US Virgin Islands, Palau, Panama, Russia, American Samoa, Vietnam, Turk and Caicos Islands and Vanuatu. States and territories referred to in Article 238-0 A 2 bis 2° of the FTC, and thus outside of the scope of the provisions of Article 244 bis B of the FTC mentioned in this paragraph, are currently Guam, US Virgin Islands, Palau, Panama, Russia, American Samoa and Vietnam.

In general, under the Treaty, a U.S. Holder who is a U.S. resident for purposes of the Treaty and entitled to Treaty benefit will not be subject to French tax on any such capital gain from the sale, exchange, repurchase or redemption by us (other than redemption proceeds which may, under certain circumstances, be partially or fully characterized as dividends under French domestic tax law or administrative guidelines and subject to the application of the Treaty) of ADSs unless such ADSs form part of the business property of a permanent establishment or fixed base that the U.S. Holder has in France. U.S. Holders who own ADSs through U.S. partnerships that are not resident for Treaty purposes are advised to consult their own tax advisors regarding their French tax treatment and their eligibility for Treaty benefits in light of their own particular circumstances.

A holder that is not a U.S. resident for Treaty purposes or is not entitled to Treaty benefit (and in both cases is not resident, established or incorporated in a non-cooperative State or territory as set out in the list referred to in Article other than those States or territories mentioned in 2° of 2 bis of the same Article 238-0 A of the FTC, unless the above mentioned safeguard clause were to apply) and has held more than 25% of our dividend rights, known as “droits aux bénéfices sociaux” at any time during the preceding five years, either directly or indirectly, and, as relates to individuals, alone or with relatives, will be subject to a levy in France at the rate of the standard corporate income tax (currently 25%), if such holder is a legal person, or 12.8%, if such holder is an individual subject to the application of any relevant tax treaty.

For a non-French resident entity that holds more than 25% of our dividend rights and may be subject to French tax on capital gains, Article 244 bis B of the FTC provides under certain conditions for a refund mechanism, allowing an eligible non-French resident corporate investor to claim a refund of the non-resident French capital gains tax to the extent such tax exceeds the amount of the French corporate income tax it would have borne if it had been a French resident. This refund mechanism is available to entities established in (i) an EU Member State or a Member State of the European Economic Area (EEA), other than a non-cooperative State or territory within the meaning of Article 238-0 A of the FTC that has concluded a tax treaty with France that includes an administrative assistance provision to combat tax fraud and tax evasion (an “EU/EEA State”) or (ii) a State, other than a non-cooperative State or territory that has concluded a tax treaty with France that includes an administrative assistance clause regarding the exchange of information aimed at combating tax fraud and tax evasion (a “Treaty State”), provided that the transferor is not effectively involved in the management or control of the entity whose shares are disposed of or redeemed. In addition, Article 244 bis B of the FTC also provides that specific collective investment funds established in EU/EEA States or Treaty States are excluded from the scope of the non-resident capital gain tax mentioned above under certain conditions.

In addition, Article 16 of the Finance Act for 2025 amended the provisions of Article 244 bis B of the FTC as to align with EU law, by allowing non-resident individuals to obtain, upon request to the French tax authorities, the reimbursement of the portion of the tax levy that exceeds the personal income tax they would have been liable for if they had been domiciled in France and had opted for the taxation of their securities income pursuant to the progressive income tax rates (benefiting, where applicable under certain conditions and limitations, from holding period allowances).

Special rules apply to U.S. Holders who are residents of more than one country.

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The discussion above is a summary of the material French tax consequences of an investment in our ADSs and is based upon laws and relevant interpretations thereof in effect as of the date hereof, all of which are subject to change, possibly with retroactive effect. It does not cover all tax matters that may be of importance to a prospective investor. Each prospective investor is urged to consult its own tax advisor about the tax consequences to it of an investment in ADSs in light of the investor’s own circumstances.

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UNDERWRITING

Leerink Partners LLC, Morgan Stanley & Co. LLC, Piper Sandler & Co. and Guggenheim Securities, LLC are acting as representatives of each of the underwriters named below and as joint bookrunning managers for this offering. Subject to the terms and conditions set forth in the underwriting agreement among us and the underwriters, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the number of ADSs (including underlying ordinary shares) set forth opposite its name below.


Underwriter	Number of ADSs
Leerink Partners LLC		2,080,000
Morgan Stanley & Co. LLC		1,760,000
Piper Sandler & Co.		1,056,000
Guggenheim Securities, LLC		768,000
LifeSci Capital LLC		448,000
Van Lanschot Kempen (USA) Inc.		288,000

Total:		6,400,000

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the ADSs sold under the underwriting agreement if any of the ADSs are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaulting underwriters may be increased or the underwriting agreement may be terminated. The underwriters may provide their services in this offering through or in conjunction with one or more of their respective affiliates.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the ADSs, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel, including the validity of the ordinary shares, including ordinary shares represented by the ADSs, and subject to other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officers’ certificates and legal opinions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Discounts and Commissions

The representatives have advised us that the underwriters propose initially to offer the ADSs to the public at the public offering price set forth on the cover page of this prospectus supplement and to dealers at that price less a concession not in excess of $3.5625 per ADS. After the initial offering of the ADSs, the public offering price, concession or any other term of this offering may be changed by the representatives.

The following table shows the per ADS public offering price, underwriting discounts and commissions, and proceeds, before expenses, to us. The total amount is shown assuming both no exercise and full exercise of the underwriters’ option to purchase up to an additional 960,000 ADSs.


			Total
	Per ADS		No Exercise		Full Exercise
Public offering price	$	125.0000	$	800,000,000	$	920,000,000
Underwriting discounts and commissions to be paid by us	$	5.9375	$	38,000,000	$	43,700,000
Proceeds, before expenses, to us	$	119.0625	$	762,000,000	$	876,300,000

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We estimate expenses payable by us in connection with this offering, other than the underwriting discounts and commissions referred to above, will be approximately $2.2 million. We have also agreed to reimburse the underwriters for certain of their expenses in an amount up to $30,000. The underwriters have also agreed to reimburse us for certain of our expenses incurred in connection with this offering.

Option to Purchase Additional ADSs

We have granted an option to the underwriters, exercisable on or before the initial settlement date, to purchase up to an aggregate of 960,000 additional ADSs at the public offering price set forth on the cover page of this prospectus supplement. If the underwriters exercise this option, each underwriter will be obligated, subject to the conditions contained in the underwriting agreement, to purchase a number of additional ADSs proportionate to that underwriter’s initial amount reflected in the above table.

No Sales of Similar Securities

We and all directors and executive officers and certain of our shareholders have agreed that, without the prior written consent of Leerink Partners LLC, Morgan Stanley & Co. LLC, Piper Sandler & Co. and Guggenheim Securities, LLC on behalf of the underwriters, we and they will not, and will not publicly disclose an intention to, during the period ending 60 days after the date of this prospectus supplement (the “restricted period”):

(i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any ADSs, ordinary shares, or any securities convertible into or exercisable or exchangeable for ADSs or ordinary shares (such other securities, including any received upon grant or vesting pursuant to a free share plan, “derivative securities”); or

(ii) enter into any hedging, swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of ADSs, ordinary shares or derivative securities, whether any such transaction described above is to be settled by delivery of ADSs, ordinary shares or derivative securities, in cash or otherwise; or

(iii) file any registration statement with the SEC relating to the offering of any ADSs, ordinary shares or derivative securities.

In addition, we and each such person agrees that, without the prior written consent of Leerink Partners LLC, Morgan Stanley & Co. LLC, Piper Sandler & Co. and Guggenheim Securities, LLC on behalf of the underwriters, we or such other person will not, during the restricted period, make any demand for, or exercise any right with respect to, the registration of any ADSs, ordinary shares or derivative securities.

With respect to us, the restrictions described above do not apply to:

(a) the sale of the ADSs offered by this prospectus supplement to the underwriters;

(b) the issuance of ADSs or ordinary shares upon the exercise of an option or warrant or the conversion of a security outstanding on the date of this prospectus supplement and described herein;

(c) the issuance of ADSs, ordinary shares, share options, free shares or warrants (including share warrants (BSA) and founder’s warrants (BSPCE)) pursuant to existing shareholder authorizations described in this prospectus supplement;

(d) the facilitating of the establishment of a trading plan on behalf of any of our shareholders, officers or directors pursuant to Rule 10b5-1 under the Exchange Act (“10b5-1 trading plan”) for the transfer of ADSs or

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ordinary shares or of the amendment of an existing 10b5-1 trading plan, provided that (i) such 10b5-1 trading plan does not provide for the transfer of ADSs or ordinary shares during the restricted period and (ii) no public announcement or filing under the Exchange Act or otherwise is required of or voluntarily made by or on behalf of the applicable individual or us regarding the establishment or amendment of such 10b5-1 trading plan;

(f) the issuance and sale of ADSs pursuant to our existing equity distribution agreement with Piper Sandler & Co., provided that any such sales may only occur at least 30 days after the date of this prospectus supplement;

(g) the entry into any agreement providing for the issuance by us of ADSs, ordinary shares or derivative securities in connection with (i) the acquisition by us of the securities, business, technology, property or other assets of another person or entity, or pursuant to an employee benefit plan assumed by us in connection with such acquisition, or (ii) joint ventures, commercial relationships or other strategic transactions, and in each case, the issuance of any such securities pursuant to any such agreement; provided, however, that the aggregate number of ADSs, ordinary shares or derivative securities that we may sell or issue or agree to sell or issue shall not exceed 5% of the total number of ordinary shares (including in the form of ADSs) issued and outstanding immediately following the completion of this offering; and provided, further, that we must cause each recipient of such securities to execute and deliver to the representatives, on or prior to the issuance of such securities, a lock-up agreement substantially in the form attached to the underwriting agreement with respect to the remainder of the restricted period and enter stop transfer instructions with our transfer agent and registrar for such securities; or

(h) the filing, after the completion of this offering, of a registration statement on Form F-6 relating to the ADSs, provided, however, that we will furnish to the representatives a copy of the proposed registration statement prior to any such filing.

In addition, with respect to our directors and executive officers and certain of our shareholders, the restrictions described above are subject to specified exceptions, including, without limitation and subject in certain cases to various conditions:

(a) transactions relating to ADSs, ordinary shares or derivative securities acquired in this offering or in open market transactions after the completion of this offering;

(b) transfers of ADSs, ordinary shares or derivative securities (i) as a bona fide gift or gifts; (ii) to any trust for the direct or indirect benefit of such person or their immediate family; (iii) as a distribution or other transfer by a partnership to its partners or former partners, by a limited liability company to its members or retired members, or by a corporation to its shareholders or former shareholders or to any wholly-owned subsidiary of such corporation; (iv) to such person’s affiliates or to any investment fund or other entity controlled or managed by such person; (v) pursuant to a qualified domestic relations order or in connection with a divorce settlement; or (vi) by will or intestate succession or intestate distribution upon the death of such person;

(c) surrender of ordinary shares to the depositary or the depositary’s custodian for the purpose of receiving an equivalent number of ADSs in lieu of such ordinary shares;

(d) transfers of ADSs, ordinary shares or derivative securities to the company in satisfaction of any tax withholding obligation;

(e) transfers or sales of up to 1,000,000 ADSs or ordinary shares (in the aggregate for all of our directors, officers and affiliates) used for the primary purpose of satisfying any withholding tax or other governmental withholding or payment obligations pursuant to equity awards granted under a share incentive plan or other equity award plan that is described in this prospectus supplement;

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(f) transfers of ADSs, ordinary shares or derivative securities to us pursuant to any contractual arrangement that provides for the repurchase of the ADSs, ordinary shares or derivative securities held by such person in connection with the termination of such person’s services to us or such person’s failure to meet certain conditions set out upon receipt of such ADSs, ordinary shares or derivative securities;

(g) the exercise or exchange by such person of any option or warrant to acquire any ADSs or ordinary shares or options to purchase ADSs or ordinary shares, in each case for cash or on a “cashless” or “net exercise” basis, pursuant to any share option, share bonus or other share plan or arrangement;

(h) the transfer of ADSs, ordinary shares or derivative securities upon the completion of a bona fide third-party tender offer, merger, consolidation or other similar transaction that is approved by our Board, made to all holders of our securities and involves a change of control of us; or

(i) the establishment of a 10b5-1 trading plan for the transfer of ADSs or ordinary shares or the amendment of an existing 10b5-1 trading plan, provided that such 10b5-1 trading plan does not provide for the transfer of ADSs or ordinary shares during the restricted period.

Leerink Partners LLC, Morgan Stanley & Co. LLC, Piper Sandler & Co. and Guggenheim Securities, LLC, in their sole discretion, may release the ADSs, ordinary shares and derivative securities subject to the lock-up agreements described above in whole or in part at any time.

Listings

Our ADSs are listed on the Nasdaq Global Market under the symbol “ABVX.” Our ordinary shares are listed on Euronext Paris under the symbol “ABVX.”

Price Stabilization, Short Positions and Penalty Bids

Until the distribution of the ADSs is completed, SEC rules may limit underwriters and selling group members from bidding for and purchasing our ADSs. However, the representatives may engage in transactions that stabilize the price of our ADSs, such as bids or purchases to peg, fix or maintain that price.

In connection with this offering, the underwriters may purchase and sell our ADSs in the open market. These transactions may include short sales, purchases on the open market to cover positions created by short sales and stabilizing transactions. Short sales involve the sale by the underwriters of a greater number of ADSs than they are required to purchase in this offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional ADSs described above. The underwriters may close out any covered short position by either exercising their option to purchase additional ADSs or purchasing ADSs in the open market. In determining the source of ADSs to close out the covered short position, the underwriters will consider, among other things, the price of ADSs available for purchase in the open market as compared to the price at which they may purchase ADSs through the option to purchase additional ADSs granted to them under the underwriting agreement described above. “Naked” short sales are sales in excess of such option. The underwriters must close out any naked short position by purchasing ADSs in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our ADSs in the open market after pricing that could adversely affect investors who purchase in this offering. Stabilizing transactions consist of various bids for or purchases of ADSs made by the underwriters in the open market prior to the closing of this offering. Such stabilization transactions will need to comply with European Union laws and notably Regulation n°596/2014 on market abuse, as amended.

The underwriters may also impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the representatives have repurchased ADSs sold by or for the account of such underwriter in stabilizing or short covering transactions.

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Similar to other purchase transactions, the underwriters’ purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our ADSs or preventing or retarding a decline in the market price of our ADSs. As a result, the price of our ADSs may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on the Nasdaq Global Market, in the over-the-counter market or otherwise.

Neither we nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our ADSs. In addition, neither we nor any of the underwriters make any representation that the representatives will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Electronic Distribution

In connection with this offering, certain of the underwriters or securities dealers may distribute prospectuses by electronic means, such as e-mail.

Settlement

Other Relationships

The underwriters and certain of their affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. Some of the underwriters and certain of their affiliates may in the future engage in investment banking and other commercial dealings in the ordinary course of business with us and our affiliates, for which they may in the future receive customary fees, commissions and expenses.

In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments. For example, Piper Sandler & Co. is the sales agent under our Equity Distribution Agreement, dated November 19, 2024, in connection with our at-the-market program.

Selling Restrictions

General

Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission in relation to the offering. This prospectus does not constitute a prospectus, product disclosure statement or other disclosure document under the

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Corporations Act 2001, or the Corporations Act, and does not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

Any offer in Australia of the securities may only be made to persons, or the Exempt Investors, who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the securities without disclosure to investors under Chapter 6D of the Corporations Act.

The securities applied for by Exempt Investors in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring securities must observe such Australian on-sale restrictions.

This prospectus contains general information only and does not take into account the investment objectives, financial situation or particular needs of any particular person. It does not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus is appropriate for their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant State”), no securities have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the securities which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that offers of the securities may be made to the public in that Relevant State at any time under the following exemptions under the Prospectus Regulation:

(a) to any legal entity which is a qualified investor as defined under the Prospectus Regulation;

(b) to fewer than 150 natural or legal persons (other than qualified investors as defined under the Prospectus Regulation), subject to obtaining the prior consent of the representatives for any such offer; or

provided that no such offer of the securities shall require us or any of our representatives to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of this provision, the expression an “offer to the public” in relation to the securities in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any securities to be offered so as to enable an investor to decide to purchase any securities, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129, as amended.

Each person in a Relevant State who receives any communication in respect of, or who acquires any securities under, the offering contemplated hereby will be deemed to have represented, warranted and agreed to and with each of the underwriters and their affiliates and to us that:

(a) it is a qualified investor within the meaning of the Prospectus Regulation; and

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(b) in the case of any securities acquired by it as a financial intermediary, as that term is used in Article 5 of the Prospectus Regulation, (i) the securities acquired by it in the offering have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in any Relevant State other than qualified investors, as that term is defined in the Prospectus Regulation, or have been acquired in other circumstances falling within the points (a) to (d) of Article 1(4) of the Prospectus Regulation and the prior consent of the representative has been given to the offer or resale; or (ii) where the securities have been acquired by it on behalf of persons in any Relevant State other than qualified investors, the offer of those securities to it is not treated under the Prospectus Regulation as having been made to such persons.

We, the underwriters and their affiliates, and others will rely upon the truth and accuracy of the foregoing representation, acknowledgement and agreement. Notwithstanding the above, a person who is not a qualified investor and who has notified the representative of such fact in writing may, with the prior consent of the representative, be permitted to acquire securities in the offering.

MiFID II Product Governance

Solely for the purposes of each manufacturer’s product approval process, the target market assessment in respect of ordinary shares has led to the conclusion that: (i) the target market for the ordinary shares is eligible counterparties, professional clients and retail clients, each as defined in Directive 2014/65/EU, as amended (“MiFID II”); and (ii) all channels for distribution of the ordinary shares to eligible counterparties, professional clients and retail clients are appropriate. Any person subsequently offering, selling or recommending the ordinary shares, or a distributor, should take into consideration the manufacturers’ target market assessment; however, a distributor subject to MiFID II is responsible for undertaking its own target market assessment in respect of the ordinary shares (by either adopting or refining the manufacturers’ target market assessment) and determining appropriate distribution channels. For the avoidance of doubt, even if the target market includes retail clients, it has been decided that the ordinary shares will only be offered to persons who meet the criteria of eligible counterparties and professional clients.

UK MiFIR Product Governance

Solely for the purposes of each manufacturer’s product approval process, the target market assessment in respect of the securities has led to the conclusion that: (i) the target market for the securities is retail clients, as defined in point (8) of article 2 of Regulation (EU) No. 2017/565 as it forms part of domestic law by virtue of the European Union (Withdrawal) Act 2018 (“EUWA”), and eligible counterparties, as defined in the Financial Conduct Authority (“FCA”) Handbook Conduct of Business Sourcebook (“COBS”) and professional clients, as defined in Regulation (EU) No 600/2014 as it forms part of domestic law by virtue of the EUWA (“UK MiFIR”); and (ii) all channels for distribution of the securities are appropriate. Any person subsequently offering, selling or recommending the securities (a “distributor”) should take into consideration the manufacturers’ target market assessment; however, a distributor subject to the FCA Handbook Product Intervention and Product Governance Sourcebook (the “UK MiFIR Product Governance Rules”) is responsible for undertaking its own target market assessment in respect of the securities (by either adopting or refining the manufacturer’s target market assessment) and determining appropriate distribution channels. For the avoidance of doubt, even if the target market includes retail clients, it has been decided that the securities will only be offered to persons who meet the criteria of eligible counterparties and professional clients.

United Kingdom

This prospectus and any other material in relation to the securities described herein is only being distributed to, and is only directed at, and any investment or investment activity to which this prospectus relates is available only to, and will be engaged in only with persons who are (i) persons having professional experience in matters relating to investments who fall within the definition of investment professionals in Article 19(5) of the FPO; or (ii) high net worth entities falling within Article 49(2)(a) to (d) of the FPO; (iii) outside the UK; or (iv) persons to

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whom an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the FSMA) in connection with the issue or sale of any securities may otherwise lawfully be communicated or caused to be communicated (all such persons together being referred to as “Relevant Persons”). The securities are only available in the UK to, and any invitation, offer or agreement to purchase or otherwise acquire the securities will be engaged in only with, the Relevant Persons. This prospectus and its contents are confidential and should not be distributed, published or reproduced (in whole or in part) or disclosed by recipients to any other person in the UK. Any person in the UK that is not a Relevant Person should not act or rely on this prospectus or any of its contents.

No securities have been offered or will be offered pursuant to the offering to the public in the UK prior to the publication of a prospectus in relation to the shares (including in the form of ADSs) which has been approved by the Financial Conduct Authority in the UK in accordance with the Public Offers and Admissions to Trading Regulations 2024 (the “POATRs”) and the FSMA, except that offers of the securities may be made to the public in the UK at any time:

(a) to any legal entity which is a “qualified investor” as defined in paragraph 15 of Schedule 1 to the POATRs;

(b) to fewer than 150 natural or legal persons (other than qualified investors as defined in paragraph 15 of Schedule 1 to the POATRs), subject to obtaining the prior consent of the underwriters for any such offer; or

provided that no such offer of the shares shall require the Company or any of the underwriters to publish a prospectus pursuant to the PROATRs or supplement a prospectus.

For the purposes of this provision, the expression an “offer to the public” in relation to the securities in the UK means the communication in any form and by any means of sufficient information on the terms of the offer and any securities to be offered so as to enable an investor to decide to purchase or subscribe for any securities.

Each person in the UK who acquires any securities in the offer or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with us, the underwriters and their affiliates that it meets the criteria outlined in this section.

France

The securities have not been and will not be offered or sold to the public in the Republic of France, and no offering of this prospectus or any marketing materials relating to securities may be made available or distributed in any way that would constitute, directly or indirectly, an offer to the public in France (except for public offerings defined in Article L.411-2 1° of the French Monetary and Financial Code).

The securities may only be offered or sold in France pursuant to Article L. 411-2 1° of the French Monetary and Financial Code to qualified investors (investisseurs qualifiés) (as such term is defined in Article 2(e) of Regulation (EU) n° 2017/1129 dated 14 June 2017, as amended ) acting for their own account, and in accordance with Articles L. 411-1, L. 411-2 and D. 411-2 to D.411-4 of the French Monetary and Financial Code.

Prospective investors are informed that:

•

neither this prospectus nor any other offering materials relating to the securities described in this prospectus has been submitted for clearance to the French financial markets authority (Autorité des marchés financiers);

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•

neither this prospectus, nor any offering material relating to the securities has been or will be released, issued, distributed or caused to be released, issued or distributed to the public in France or used in connection with any offer for subscription or sale of the securities to the public in France within the meaning of Article L. 411-1 of the French Monetary and Financial Code (other than public offerings defined in Article L.411-2 1° of the French Monetary and Financial Code);

•

individuals or entities referred to in Article L. 411-2 1° of the French Monetary and Financial Code may participate in the offering, as provided under Articles D.411-4 of the French Monetary and Financial Code; and

•

the direct and indirect distribution or sale to the public of the securities acquired by them may only be made in compliance with Articles L. 411-1, L. 411-2 1°, L. 412-1 and L. 621-8 to L. 621-8-2 of the French Monetary and Financial Code.

Canada

The securities may be sold in Canada only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the securities must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Dubai International Financial Centre

This prospectus relates to an Exempt Offer in accordance with the Offered Securities Rules of the Dubai Financial Services Authority, or the DFSA. This prospectus is intended for distribution only to persons of a type specified in the Offered Securities Rules of the DFSA. It must not be delivered to, or relied on by, any other person. The DFSA has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus nor taken steps to verify the information set forth herein and has no responsibility for the prospectus. The securities to which this prospectus relates may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the securities offered should conduct their own due diligence on the securities. If you do not understand the contents of this prospectus you should consult an authorized financial advisor.

Hong Kong

The securities have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (i) to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made under that Ordinance; or (ii) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that

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Ordinance. No advertisement, invitation or document relating to our securities has been or may be issued or has been or may be in the possession of any person for the purposes of issuance, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to our securities which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the Securities and Futures Ordinance and any rules made under that Ordinance.

Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968, or the Israeli Securities Law, and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus is being distributed only to, and is directed only at, and any offer of the securities hereunder is directed only at, (i) a limited number of persons in accordance with the Israeli Securities Law and (ii) investors listed in the first addendum to the Israeli Securities Law, or the Addendum, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange, underwriters, venture capital funds, entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case, purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors are required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

Japan

No registration pursuant to Article 4, paragraph 1 of the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended), or the FIEL, has been made or will be made with respect to the solicitation of the application for the acquisition of the securities.

Accordingly, the securities have not been, directly or indirectly, offered or sold and will not be, directly or indirectly, offered or sold in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan) or to others for re-offering or re-sale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan except pursuant to an exemption from the registration requirements, and otherwise in compliance with, the FIEL and the other applicable laws and regulations of Japan.

For Qualified Institutional Investors, or QII

Please note that the solicitation for newly-issued or secondary securities (each as described in Paragraph 2, Article 4 of the FIEL) in relation to the securities constitutes either a “QII only private placement” or a “QII only secondary distribution” (each as described in Paragraph 1, Article 23-13 of the FIEL). Disclosure regarding any such solicitation, as is otherwise prescribed in Paragraph 1, Article 4 of the FIEL, has not been made in relation to the securities. The securities may only be transferred to QIIs.

For Non-QII Investors

Please note that the solicitation for newly-issued or secondary securities (each as described in Paragraph 2, Article 4 of the FIEL) in relation to the securities constitutes either a “small number private placement” or a “small number private secondary distribution” (each as is described in Paragraph 4, Article 23-13 of the FIEL). Disclosure regarding any such solicitation, as is otherwise prescribed in Paragraph 1, Article 4 of the FIEL, has not been made in relation to the securities. The securities may only be transferred en bloc without subdivision to a single investor.

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Singapore

This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the securities may not be circulated or distributed, nor may the securities be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore, or the SFA, (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the securities are subscribed or purchased under Section 275 of the SFA by a relevant person which is (a) a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or (b) a trust (where the trustee is not an accredited investor ) the sole purpose of which is to hold investments and each beneficiary of the trust is an individual who is an accredited investor, securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the securities pursuant to an offer made under Section 275 of the SFA except:

(i) to an institutional investor or to a relevant person defined in Section 275(2) of the SFA, or to any person arising from an offer referred to in Section 275(1A) or Section 276(4)(i)(B) of the SFA; (ii) where no consideration is or will be given for the transfer; (iii) where the transfer is by operation of law; (iv) as specified in Section 276(7) of the SFA; or (v) as specified in Regulation 37A of the Securities and Futures (Offers of Investments) (Securities and Securities-based Derivatives Contracts) Regulations 2018.

Solely for the purposes of its obligations pursuant to Section 309B of the SFA, we have determined, and hereby notify all relevant persons (as defined in the CMP Regulations 2018), that the shares are “prescribed capital markets products” (as defined in the CMP Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products and MAS Notice FAA-N16: Notice on Recommendations on Investment Products).

Switzerland

This prospectus is not intended to constitute an offer or solicitation to purchase or invest in our securities. Our securities may not be publicly offered, directly or indirectly, in Switzerland within the meaning of the Swiss Financial Services Act, or the FinSA, and no application has or will be made to admit our securities to trading on any trading venue (exchange or multilateral trading facility) in Switzerland. Neither this prospectus nor any other offering or marketing material relating to our securities constitutes a prospectus pursuant to the FinSA, and neither this prospectus nor any other offering or marketing material relating to our securities may be publicly distributed or otherwise made publicly available in Switzerland.

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MATERIAL CHANGES

Except as described in this prospectus supplement or otherwise described in our Annual Report and in our reports on Form 6-K incorporated by reference into this prospectus supplement, no reportable material changes have occurred since December 31, 2025.

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ENFORCEMENT OF CIVIL LIABILITIES

We are a société anonyme, organized under the laws of France. The majority of our directors and officers are residents of countries other than the United States, and the majority of our assets are located outside of the United States. We have appointed an agent for service of process in the United States.

Accordingly, U.S. investors may find it difficult and may be unable:

•

to obtain jurisdiction over us or our non-U.S. resident officers and directors in U.S. courts in actions predicated on the civil liability provisions of the U.S. federal securities laws;

•

to enforce judgments obtained in such actions against us or our non-U.S. resident officers and directors;

•

to bring an original action in a French court to enforce liabilities based upon the U.S. federal securities laws against us or our officers or directors; and

•

to enforce against us or our officers or directors in non-U.S. courts, including French courts, judgments of U.S. courts predicated upon the civil liability provisions of the U.S. federal securities laws.

In addition, actions in the United States under U.S. federal securities laws could be affected under certain circumstances by French Law No. 68-678 of July 26, 1968 (relating to the communication of documents and information of an economic, commercial, industrial, financial or technical nature to foreign authorities or persons), as amended by French Law No. 80-538 of July 16, 1980, and French Ordinance No. 2000-916 of September 19, 2000, and as further specified by Decree No. 2022-707 of February 18, 2022 and Order of March 7, 2022, which may preclude or restrict the obtaining of evidence in France or from French persons in connection with those actions. As a result of the above regulations, the U.S. authorities would have to comply with applicable international treaties or agreements and laws and regulations in force (such as the 1970 Hague Convention on the Taking of Evidence Abroad).

Similarly, French data protection rules (Law No. 78-17 of January 6, 1978 on data processing, data files and individual liberties, as modified) and the General Data Protection Regulation (i.e., Regulation (EU) 2016/679 of the European Parliament and of the Council of April 27, 2016) can limit under certain circumstances the possibility of obtaining information in France or from French persons in connection with a U.S. action.

Nevertheless, a final judgment for the payment of money rendered by any federal or state court in the United States based on civil liability, whether or not predicated solely upon the U.S. federal securities laws, would be recognized and be enforceable in France provided that a French judge considers that this judgment meets the requirements under the French rules of international private law concerning the recognition and the enforcement of foreign judgments and is capable of being immediately enforced in the United States. A French court is therefore likely to grant the enforcement of a foreign judgment without a review of the substantive matters thereby adjudicated, only if: (1) the United States federal or state court has jurisdiction and the dispute is clearly connected to the territory of the court which rendered the judgment (2) the judgment is not tainted by fraud, (3) the judgment complies with French substantive and procedural rules of international public policy (ordre public international), including principles of due process (principe du contradictoire) and notably the right to a fair trial, and (4) the judgment is not irreconcilable with an earlier judgment rendered or recognized by a French court in the same or related matter. The French court may require all relevant supporting documents to be translated into the French language by a “sworn translator” (traducteur assermenté) as a condition to their admissibility into evidence or for purposes of enforcement. The decision granting exequatur is subject to appeal, with the appeal court decision also being rendered on the basis of the above-mentioned criteria.

In addition, French law guarantees full compensation for the harm suffered but is limited to the actual damages, so that the victim does not suffer or benefit from the situation. Such system excludes damages such as, but not limited to, punitive and exemplary damages. Therefore, there is some uncertainty as to whether a foreign judgment awarding punitive and exemplary damages well above actual damages would be granted enforcement in France.

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As a result, the enforcement, by U.S. investors, of any judgments obtained in U.S. courts in civil and commercial matters, including judgments under the U.S. federal securities law against us or members of our Board, officers or certain experts named herein who are residents of France or countries other than the United States would be subject to the above conditions.

Finally, if an original action is brought in France, French courts may refuse to apply foreign law designated by the applicable French rules of conflict (including the law chosen by the parties to govern their contract) if the application of such law is deemed to contravene French international public policy or in case of overriding mandatory rules (as determined on a case by case basis by French courts) or, where all other elements relevant to the situation at the time of the choice are located in a country other than the country whose law has been chosen, the choice of the parties shall not prejudice the application of provisions of the law of that other country which cannot be derogated from by agreement. Furthermore, in an action brought in France on the basis of U.S. federal or state securities laws, French courts may not have the requisite power to grant all the remedies sought.

As a result, there may be doubt as to whether a French court would impose civil liability on us, the members of our Board, our officers or certain experts named herein in an original action predicated solely upon the U.S. federal securities laws brought in a court of competent jurisdiction in France against us or such members, officers or experts, respectively.

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LEGAL MATTERS

Cooley LLP, New York, New York, is representing us in regards to certain matters governed by U.S. law in connection with this offering. The validity of our ordinary shares, including ordinary shares represented by the ADSs, and certain other matters governed by French law is being passed on for us by Orrick, Herrington & Sutcliffe (Europe) LLP, Paris, France. Latham & Watkins LLP, New York, New York, is representing the underwriters in connection with the offering with respect to U.S. federal law, and Gide Loyrette Nouel A.A.R.P.I. is representing the underwriters in connection with the offering with respect to French law.

EXPERTS

The consolidated financial statements incorporated in this prospectus supplement by reference to the Annual Report on Form 20-F for the year ended December 31, 2025 have been so incorporated in reliance on the report of PricewaterhouseCoopers Audit, an independent registered public accounting firm, given on the authority of said firm as experts in accounting and auditing.

The offices of PricewaterhouseCoopers Audit are located at 63, rue de Villiers, 92208 Neuilly-sur-Seine, France.

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WHERE YOU CAN FIND ADDITIONAL INFORMATION

We have filed with the SEC a registration statement on Form F-3 under the Securities Act with respect to the securities described in this prospectus supplement. A related registration statement on Form F-6 has been filed with the SEC to register the ADSs. This prospectus supplement and the accompanying prospectus, which forms a part of the registration statement, do not contain all of the information included in the registration statement.

The SEC maintains a website (http://www.sec.gov) that contains reports and other information regarding registrants, such as Abivax, that file electronically with the SEC.

We are subject to the information reporting requirements of the Exchange Act applicable to foreign private issuers and under those requirements file reports with the SEC. Accordingly, we are required to file or furnish reports and other information with the SEC, including Annual Reports on Form 20-F and Reports on Form 6-K. As a foreign private issuer, we are exempt from the rules under the Exchange Act related to the furnishing and content of proxy statements, and our executive officers, board members and principal shareholders are exempt from “short-swing” profit recovery provisions contained in Section 16 of the Exchange Act. In addition, we are not required under the Exchange Act to file periodic reports and financial statements with the SEC as frequently or as promptly as United States companies whose securities are registered under the Exchange Act.

We maintain a corporate website at www.abivax.com. Information contained on, or that can be accessed through, our website does not constitute a part of this prospectus. We have included our website address in this prospectus solely as an inactive textual reference.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information that we file with them. Incorporation by reference allows us to disclose important information to you by referring you to those other documents. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We filed a registration statement on Form F-3 under the Securities Act of 1933, as amended, with the SEC with respect to the securities we may offer pursuant to this prospectus. This prospectus omits certain information contained in the registration statement, as permitted by the SEC. You should refer to the registration statement, including the exhibits, for further information about us and the securities we may offer pursuant to this prospectus. Statements in this prospectus regarding the provisions of certain documents filed with, or incorporated by reference in, the registration statement are not necessarily complete and each statement is qualified in all respects by that reference. Copies of all or any part of the registration statement, including the documents incorporated by reference or the exhibits, may be obtained upon payment of the prescribed rates at the offices of the SEC listed above in “Where You Can Find Additional Information.” The documents we are incorporating by reference are:

•

our Annual Report on Form 20-F for the fiscal year ended December 31, 2025, filed with the SEC on March 23, 2026;

•

our Reports on Form 6-K filed with the SEC on February 23, 2026, April 20, 2026, May 7, 2026, May 20, 2026, May 22, 2026, June 2, 2026 and June 29, 2026, solely to the extent the information in such reports has been incorporated by reference into the registration statement of which this prospectus supplement forms a part; and

•

the description of ADSs representing our ordinary shares contained in our Registration Statement on Form 8-A filed with the SEC on October 18, 2023, including any amendments or reports filed for the purpose of updating such description, including Exhibit 2.3 to our Annual Report on Form 20-F for the fiscal year ended December 31, 2025, filed with the SEC on March 23, 2026.

We are also incorporating by reference all subsequent Annual Reports on Form 20-F that we file with the SEC and certain reports on Form 6-K that we furnish to the SEC after the date of this prospectus (if they state that they are incorporated by reference into this prospectus) prior to the termination of the offering of securities under this prospectus. In all cases, you should rely on the later information over different information included in this prospectus or any accompanying prospectus supplement. The SEC file number for the documents incorporated by reference into this prospectus supplement is 001-41842.

Unless expressly incorporated by reference, nothing in this prospectus supplement shall be deemed to incorporate by reference information furnished to, but not filed with, the SEC. Copies of all documents incorporated by reference in this prospectus supplement and the accompanying prospectus, other than exhibits to those documents unless such exhibits are specifically incorporated by reference in this prospectus supplement, will be provided at no cost to each person, including any beneficial owner, who receives a copy of this prospectus supplement and the accompanying prospectus on the written or oral request of that person made to:

Abivax SA

7-11 Boulevard Haussmann

75009 Paris

France

Tel: +33 1 53 83 09 63

You may also access these documents on our website, www.abivax.com. The information contained on, or that can be accessed through, our website is not a part of this prospectus. We have included our website address in this prospectus solely as an inactive textual reference.

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You should rely only on information contained in, or incorporated by reference into, this prospectus. We have not authorized anyone to provide you with information different from that contained in this prospectus or incorporated by reference in this prospectus. We are not making offers to sell the securities in any jurisdiction in which such an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make such offer or solicitation.

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PROSPECTUS

LOGO

Ordinary Shares

American Depositary Shares representing Ordinary Shares

Warrants to Purchase Ordinary Shares or American Depositary Shares

Debt Securities

We and/or any selling security holder may offer and sell from time to time the securities described in this prospectus, either individually or in any combination, in one or more offerings at prices and on terms that will be determined at the time of the offering.

This prospectus describes the general terms of these securities and the general manner in which these securities will be offered. We will provide you with the specific terms of any offering in one or more supplements to this prospectus. We and/or our selling security holders may offer these securities in amounts, at prices and on terms determined at the time of offering. We and/or our selling security holders may sell the securities through public or private transactions directly to you, through agents, or through underwriters and dealers on or off the Nasdaq Global Market. The prospectus supplements will also describe the specific manner in which these securities will be offered and may also supplement, update or amend information contained in this document. You should read this prospectus and any prospectus supplement, as well as any documents incorporated by reference into this prospectus or any prospectus supplement, carefully before you invest.

Our securities may be sold directly by us or any selling security holders to you, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section titled “Plan of Distribution” in this prospectus and in the applicable prospectus supplement. Other than any securities sold in connection with a rights offering, we will only sell securities pursuant to this prospectus for which preferential subscription rights shall have been waived by our shareholders in accordance with French law. If any underwriters or agents are involved in the sale of our securities with respect to which this prospectus is being delivered, the names of such underwriters or agents and any applicable fees or commissions and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds that we expect to receive from such sale will also be set forth in a prospectus supplement.

Our ADSs are listed on the Nasdaq Global Market under the symbol “ABVX.” On June 29, 2026, the last reported sale price of the ADSs on the Nasdaq Global Market was $96.15 per ADS. Our ordinary shares are listed on Euronext Paris under the symbol “ABVX.” On June 29, 2026, the closing price of our ordinary shares on Euronext Paris was €83.30 per ordinary share. Each ADS represents the right to receive one ordinary share, and the ADSs may be evidenced by American Depositary Receipts (“ADRs”). The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the Nasdaq Global Market or any securities market or other securities exchange of the securities covered by the prospectus supplement. There is currently no market through which warrants may be sold, and purchasers may not be able to resell warrants purchased under this prospectus. This may affect the pricing of any warrants in the secondary market, the transparency and availability of trading prices, the liquidity of the warrants and the extent of issuer regulation. Prospective purchasers of our securities are urged to obtain current information as to the market prices of our securities, where applicable.

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks that we have described under the caption “Risk Factors” on page 6 of this prospectus and in our most recent Annual Report on Form 20-F and any other reports or documents incorporated by reference into this prospectus. We may also include specific risk factors in supplements to this prospectus under the caption “Risk Factors.” This prospectus may not be used to sell our securities unless accompanied by a prospectus supplement.

Owning our securities may subject you to tax consequences both in France and in the United States. This prospectus and any applicable prospectus supplement may not describe these tax consequences fully. You should read the tax discussion in any applicable prospectus supplement. In addition, your ability to enforce civil liabilities under U.S. federal securities laws may be affected adversely by the fact that we are incorporated under the laws of France, many of the members of our board of directors and experts named in this prospectus are residents of France or elsewhere outside of the United States, and a substantial portion of our assets and the assets of such persons are located outside the United States. See “Enforcement of Civil Liabilities.”

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is June 30, 2026.

TABLE OF CONTENTS


	PAGE
ABOUT THIS PROSPECTUS		1
PROSPECTUS SUMMARY		3
RISK FACTORS		6
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		7
USE OF PROCEEDS		9
SELLING SECURITY HOLDERS		10
PLAN OF DISTRIBUTION		11
DESCRIPTION OF SHARE CAPITAL		13
LIMITATIONS AFFECTING SHAREHOLDERS OF A FRENCH COMPANY		32
DESCRIPTION OF AMERICAN DEPOSITARY SHARES		34
DESCRIPTION OF WARRANTS		45
DESCRIPTION OF DEBT SECURITIES		46
TAXATION		53
LEGAL MATTERS		54
EXPERTS		54
ENFORCEMENT OF CIVIL LIABILITIES		55
WHERE YOU CAN FIND MORE INFORMATION		57
INCORPORATION OF DOCUMENTS BY REFERENCE		58
EXPENSES ASSOCIATED WITH REGISTRATION		59

ABOUT THIS PROSPECTUS

This prospectus is part of an automatic registration statement on Form F-3 that we filed with the SEC using a “shelf” registration process available to us as a “well-known seasoned issuer,” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”). Under this shelf registration process, we may offer ordinary shares, including ordinary shares represented by ADSs, warrants to purchase ordinary shares or ADSs, and debt securities, either individually or in combination, in one or more offerings. No limit exists on the aggregate number or amount of securities we may sell pursuant to the registration statement of which this prospectus is a part. This prospectus provides you with a general description of the securities we may offer.

Under this shelf registration process, we and/or our selling security holders may offer the securities described in this prospectus from time to time at prices and on terms to be determined by market conditions at the time of offering. Registration of the securities covered by this prospectus does not mean that these securities will necessarily be offered or sold. This prospectus provides you with a general description of the securities we and/or our selling security holders may offer. Each time we and/or our selling security holders offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities.

Each time we and/or our selling security holders sell securities under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in any documents that we have incorporated by reference into this prospectus. You should read this prospectus, any applicable prospectus supplement and any related free writing prospectus, together with the information incorporated herein by reference as described under the heading “Incorporation of Documents by Reference,” before investing in any of the securities offered.

THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

Neither we, nor any agent, underwriter or dealer, has authorized any person to give any information or to make any representation other than those contained in or incorporated by reference into this prospectus, any applicable prospectus supplement or any related free writing prospectus prepared by or on behalf of us or to which we have referred you. This prospectus, any applicable supplement to this prospectus or any related free writing prospectus does not constitute an offer to sell or the solicitation of an offer to buy any securities other than the registered securities to which it relates, nor does this prospectus, any applicable supplement to this prospectus or any related free writing prospectus constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction.

You should not assume that the information contained in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate on any date subsequent to the date set forth on the front of the document or that any information we have incorporated by reference is correct on any date subsequent to the date of the document incorporated by reference, even though this prospectus, any applicable prospectus supplement or any related free writing prospectus is delivered, or securities are sold, on a later date.

This prospectus and the information incorporated herein by reference contain summaries of certain provisions contained in some of the documents described herein, but you should refer to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the heading “Where You Can Find More Information.”

Unless otherwise indicated in this prospectus, “Abivax,” “the Company,” “our Company,” “we,” “us” and “our” refer to Abivax SA and its consolidated subsidiary, taken as a whole.

In this prospectus, references to “euro” or “€” are to the legal currency of the countries of the European Union, including the Republic of France, and references to “dollars,” “U.S. dollars” or “$” are to the legal currency of the United States of America.

PROSPECTUS SUMMARY

The following summary highlights information contained elsewhere in this prospectus and does not contain all of the information that you need to consider in making your investment decision. We urge you to read this entire prospectus, including the more detailed consolidated financial statements, notes to the consolidated financial statements and other information incorporated by reference from our other filings with the SEC or included in any applicable prospectus supplement or free writing prospectus. Investing in our securities involves risks. Therefore, carefully consider the risk factors set forth in any prospectus supplements and in our most recent filings with the SEC including our Annual Reports on Form 20-F and reports on Form 6-K, as well as other information in this prospectus and any prospectus supplements and the documents incorporated by reference herein or therein, before purchasing our securities. Each of the risk factors could adversely affect our business, operating results and financial condition, as well as adversely affect the value of an investment in our securities.

Company Overview

Our lead drug candidate, obefazimod, is currently being developed for the treatment of moderately to severely active UC and CD. We are also evaluating potential combination therapy opportunities in IBD to pursue. In parallel, we are in the process of strengthening our development portfolio by generating follow-on compounds based on our miR-124 platform and assessing external early drug candidates in IBD.

Corporate Information

Our ADSs began trading on the Nasdaq Global Market in October 2023.

The SEC maintains a website that contains reports, proxy information statements and other information regarding issuers that file electronically with the SEC. The address of that site is www.sec.gov. Our website address is www.abivax.com. The reference to our website is an inactive textual reference only and information contained in, or that can be accessed through, our website or any other website cited in this prospectus is not part of this prospectus.

Implications of Being an Emerging Growth Company

We qualify as an “emerging growth company” as defined in the U.S. Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). As an emerging growth company, we may take advantage of specified reduced disclosure and other requirements that are otherwise applicable generally to public companies. These provisions include:

•

exemption from the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act of 2002; and

•

We may take advantage of these provisions until December 31, 2028 or until such earlier time that we no longer qualify as an emerging growth company. We would cease to be an emerging growth company upon the earliest to occur of: (i) the last day of the fiscal year in which our annual gross revenues exceed $1.235 billion; (ii) the first day of the year following the first year in which, as of the last business day of our most recently completed second fiscal quarter, the market value of our common equity held by non-affiliates exceeds $700 million; (iii) the date on which we have issued more than $1.0 billion in non-convertible debt securities during the previous three years; and (iv) the last day of the fiscal year ending after the fifth anniversary of our initial public offering of our ADSs.

We may choose to take advantage of some but not all of these exemptions. For example, Section 107 of the JOBS Act provides that an emerging growth company can use the extended transition period provided in Section 7(a)(2)(B) of the Securities Act, for complying with new or revised accounting standards. Given that we currently report and expect to continue to report under IFRS, as issued by the IASB, we have irrevocably elected not to avail ourselves of this extended transition period, and, as a result, we will adopt new or revised accounting standards on the relevant dates on which adoption of such standards is required by the IASB. Since IFRS make no distinction between public and private companies for purposes of compliance with new or revised accounting standards, the requirements for our compliance as a private company and as a public company are the same.

Implications of Being a Foreign Private Issuer

We are also considered a “foreign private issuer” under U.S. securities laws. In our capacity as a foreign private issuer, we are exempt from certain rules under the U.S. Securities Exchange Act of 1934, as amended (the “Exchange Act”), that impose certain disclosure obligations and procedural requirements for proxy solicitations under Section 14 of the Exchange Act. In addition, members of our board of directors and our principal shareholders are exempt from the “short-swing” profit recovery provisions of Section 16 of the Exchange Act and the rules under the Exchange Act with respect to their purchases and sales of our securities. Moreover, we are not required to file periodic reports and financial statements with the SEC as frequently or as promptly as U.S. companies whose securities are registered under the Exchange Act. In addition, we are not required to comply with Regulation FD, which restricts the selective disclosure of material information.

The Securities We and/or Our Selling Security Holders May Offer

Under this prospectus, we and/or our selling security holders may offer ordinary shares, including ADSs representing our ordinary shares, warrants to purchase ordinary shares or ADSs, and debt securities, either individually or in any combination, from time to time at prices and on terms to be determined by market conditions at the time of the offering. This prospectus provides you with a general description of the securities we and/or our selling security holders may offer. Each time we and/or our selling security holders offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

•

designation or classification;

•

aggregate principal amount or aggregate offering price;

•

maturity, if applicable;

•

original issue discount;

•

rates and times of payment of interest or dividends, if any;

•

redemption, conversion or sinking fund terms, if any;

•

conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates in the securities or other property receivable upon conversion or exchange;

•

ranking, if applicable;

•

restrictive covenants, if any;

•

voting or other rights, if any; and

•

conversion or exercise prices, if any.

The prospectus supplement also may add, update or change information contained in this prospectus or in documents we have incorporated by reference into this prospectus. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness.

We and/or our selling security holders may sell the securities directly to investors or to or through agents, underwriters or dealers. We, and our agents or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we and/or our selling security holders offer securities through agents or underwriters, we will include in the applicable prospectus supplement:

•

the names of those agents or underwriters;

•

applicable fees and commissions to be paid to them;

•

details regarding over-allotment options, if any; and

•

the net proceeds to us or our selling security holders.

This prospectus may not be used to consummate a sale of any securities unless it is accompanied by a prospectus supplement.

RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully review the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in our most recent Annual Report on Form 20-F as updated by our subsequent filings including our Reports on Form 6-K that are incorporated by reference into this prospectus, before deciding whether to purchase any of the securities being registered pursuant to the registration statement of which this prospectus is a part. Each of the risk factors could adversely affect our business, results of operations, financial condition and cash flows, as well as adversely affect the value of an investment in our securities, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Exchange Act and the Private Securities Litigation Reform Act of 1995. All statements other than present and historical facts and conditions, including statements regarding our future results of operations and financial position, business strategy, plans and our objectives for future operations, are forward-looking statements. When used in this prospectus and the documents incorporated by reference, the words “anticipate,” “believe,” “can,” “could,” “estimate,” “expect,” “intend,” “is designed to,” “may,” “might,” “objective,” “plan,” “potential,” “predict,” “should,” “will,” “would” or the negative of these and similar expressions identify forward-looking statements. Forward-looking statements include, but are not limited to, statements about:

•

the prospects of attaining, maintaining and expanding marketing authorization for our lead drug candidate, obefazimod;

•

the potential attributes and clinical advantages of obefazimod and our future drug candidates;

•

the initiation, timing, progress and results of our preclinical and clinical trials (and those conducted by third parties) and other research and development programs;

•

the timing of the availability of data from our clinical trials, including our Phase 3 maintenance trial of obefazimod in moderately to severely active ulcerative colitis and Phase 2b trial of obefazimod in CD;

•

the timing of and our ability to advance drug candidates through clinical development;

•

the timing or likelihood of regulatory meetings and filings;

•

the timing of and our ability to obtain and maintain regulatory approvals for obefazimod and any of our future drug candidates;

•

our ability to identify and develop new drug candidates from our preclinical studies;

•

our ability to develop sales and marketing capabilities and transition into a commercial-stage company;

•

the effects of increased competition as well as innovations by new and existing competitors in our industry;

•

our ability to enter into strategic relationships or partnerships;

•

our ability to obtain, maintain, protect and enforce our intellectual property rights and propriety technologies and to operate our business without infringing the intellectual property rights and proprietary technology of third parties;

•

our estimates regarding expenses, future revenues, capital requirements and the need for additional financing;

•

the impact of government laws and regulations;

•

our competitive position;

•

other risks and uncertainties indicated in this prospectus and the documents incorporated by reference herein, including those under the heading “Risk Factors,” and the other documents filed or to be filed with the SEC by us.

You should refer to the “Risk Factors” section contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into

this prospectus, for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. As a result of these factors, we cannot assure you that the forward-looking statements in this prospectus will prove to be accurate. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame or at all.

Except as required by law, we undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise.

You should read this prospectus and the documents that we reference in this prospectus and have filed as exhibits to this prospectus completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

This prospectus contains market data and industry forecasts that were obtained from industry publications. These data involve a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. We have not independently verified any third-party information. While we believe the market position, market opportunity and market size information included in this prospectus is generally reliable, such information is inherently imprecise.

USE OF PROCEEDS

We will retain broad discretion over the use of the net proceeds from the sale of the securities we offer pursuant to this prospectus. We will set forth in the applicable prospectus supplement or free writing prospectus our intended use for the net proceeds received from the sale of any securities sold pursuant to the prospectus supplement or free writing prospectus. Pending these uses, we intend to invest the net proceeds in a variety of capital preservation investments, including short-term, investment-grade, interest-bearing instruments.

We will not receive any proceeds from the sale by selling security holders of the securities covered by this prospectus.

SELLING SECURITY HOLDERS

Selling security holders are persons or entities that, directly or indirectly, have acquired or will from time to time acquire from us, our securities. Such selling security holders may be parties to registration rights agreements with us, or we otherwise may have agreed or will agree to register their securities for resale. The initial purchasers of our securities, as well as their transferees, pledges, donees or successors, all of whom we refer to as “selling security holders,” may from time to time offer and sell our securities pursuant to this prospectus and any applicable prospectus supplement.

The applicable prospectus supplement will set forth the name of each of the selling security holders and the number of securities beneficially owned by such selling security holders that are covered by such prospectus supplement. The applicable prospectus supplement will also disclose whether any of the selling security holders has held any position or office with, has been employed by or otherwise has had a material relationship with us during the three years prior to the date of the applicable prospectus supplement.

PLAN OF DISTRIBUTION

We and/or our selling security holders may offer securities under this prospectus from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods. We and/or our selling security holders may sell the securities (1) through underwriters or dealers, (2) through agents and/or (3) directly to one or more purchasers. We and/or our selling security holders may distribute the securities from time to time in one or more transactions, in accordance with applicable law and regulations and existing shareholders delegations of authority, at:

•

a fixed price or prices, which may be changed from time to time;

•

market prices prevailing at the time of sale;

•

prices related to such prevailing market prices; or

•

negotiated prices.

The distribution of securities may be carried out, from time to time, in one or more transactions, including:

•

to or through underwriters;

•

block transactions and transactions on the Nasdaq Global Market or any other organized market where such securities may be traded;

•

purchases by a broker-dealer as principal and resale by the broker-dealer for its own account pursuant to a prospectus supplement;

•

ordinary brokerage transactions and transactions in which a broker-dealer solicits purchasers;

•

sales through an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act, into an existing trading market, on an exchange or otherwise; or

•

sales in other ways not involving market makers or established trading markets, including direct sales to purchasers.

Each time that we and/or our selling security holders sell securities covered by this prospectus, we will provide a prospectus supplement or supplements that will describe the method of distribution and set forth the terms and conditions of the offering of such securities, including the offering price of the securities and the proceeds to us, if applicable.

We and/or our selling security holders may directly solicit offers to purchase the securities being offered by this prospectus. We and/or our selling security holders may also designate agents to solicit offers to purchase the securities from time to time. We will name in a prospectus supplement any underwriter or agent involved in the offer or sale of the securities.

If we and/or our selling security holders utilize a dealer in the sale of the securities being offered by this prospectus, we and/or our selling security holders will sell the securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale.

If we and/or our selling security holders utilize an underwriter in the sale of the securities being offered by this prospectus, we and/or our selling security holders will execute an underwriting agreement with the underwriter at the time of sale, and we will provide the name of any underwriter in the prospectus supplement that the underwriter will use to make resales of the securities to the public. In connection with the sale of the securities, we, or the purchasers of the securities for whom the underwriter may act as agent, may compensate the underwriter in the form of underwriting commissions. The underwriter may sell the securities to or through dealers, and the underwriter may compensate those dealers in the form of concessions or commissions from the underwriters and/or commissions from the purchasers for which they may act as agent. Unless otherwise indicated in a prospectus supplement, an agent will be acting on a best efforts basis and a dealer will purchase securities as a principal, and may then resell the securities at varying prices to be determined by the dealer.

We will provide in the applicable prospectus supplement information regarding any compensation we pay to underwriters, dealers or agents in connection with the offering of the securities, and any concessions or commissions allowed by underwriters to participating dealers. Underwriters, dealers and agents participating in the distribution of the securities may be deemed to be underwriters within the meaning of the Securities Act of 1933, as amended, and any commissions received by them and any profit realized by them on resale of the securities may be deemed to be underwriting commissions. We may enter into agreements to indemnify underwriters, dealers and agents against civil liabilities, including liabilities under the Securities Act, or to contribute to payments they may be required to make in respect thereof.

Sales to or through one or more underwriters or agents in at-the-market offerings will be made pursuant to the terms of a distribution agreement with the underwriters or agents. Such underwriters or agents may act on an agency basis or on a principal basis. During the term of any such agreement, shares may be sold on a daily basis on any stock exchange, market or trading facility on which the ADSs are traded, in negotiated transactions or otherwise as agreed with the underwriters or agents. The distribution agreement will provide that any ADSs sold will be sold at negotiated prices or at prices related to the then prevailing market prices for our ADSs. Therefore, exact figures regarding proceeds that will be raised or commissions to be paid cannot be determined at this time and will be described in a prospectus supplement. Pursuant to the terms of the distribution agreement, we may also agree to sell, and the relevant underwriters or agents may agree to solicit offers to purchase, blocks of our ADSs or other securities. The terms of each such distribution agreement will be described in a prospectus supplement.

In order to facilitate the offering of the securities, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. This may include over-allotments or short sales of the securities, which involve the sale by persons participating in the offering of more securities than were sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option. In addition, these persons may stabilize or maintain the price of the securities by bidding for or purchasing the applicable security in the open market or by imposing penalty bids, whereby selling concessions allowed to dealers participating in the offering may be reclaimed if the securities sold by them are repurchased in connection with stabilization transactions. The effect of these transactions may be to stabilize or maintain the market price of the securities at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

The underwriters, dealers and agents may engage in other transactions with us, or perform other services for us, in the ordinary course of their business.

DESCRIPTION OF SHARE CAPITAL

General

We were incorporated as a société anonyme (limited liability company) on December 4, 2013 and registered at the Paris Trade and Company Register on December 27, 2013 for a period of 99 years until December 22, 2112, subject to extension or early dissolution, under the number 799 363 718. Our corporate purpose in France and abroad includes the research, development and marketing of therapeutic and prophylactic vaccines and small therapeutic molecules that primarily have applications in the anti-infective field, as set forth in Article 4 of our by-laws. We may participate, by any means, directly or indirectly in any operations that may be related to our purpose through the creation of new companies, contribution, subscription or purchase of company securities or rights, merger or otherwise, creation, acquisition, leasing, management lease of any businesses or establishments. Our principal executive offices are located at 7-11 boulevard Haussmann, 75009 Paris, France, and our telephone number is +33 (0) 1 53 83 09 63.

The following description of our by-laws and share capital does not purport to be complete and is qualified in its entirety by reference to our by-laws as of the date of this prospectus. Copies of our by-laws may be obtained from the Trade and Company Registry (Greffe du Registre du Commerce et des Sociétés) of Paris, France or our corporate headquarters and are filed as an exhibit to this registration statement of which this prospectus forms a part.

Share Capital

Share Capital History

As of March 31, 2026, our share capital amounted to €792,911.88 and is divided into 79,291,188 ordinary shares of €0.01 par value each after taking into account:


	Number of Shares		Par Value		Amount of Paid Up Capital
			(€)		(€)
Ordinary Shares		79,291,188		0.01	€	792,911.88

Total		79,291,188		0.01	€	792,911.88

All of the shares are fully subscribed and paid. As of the date of this prospectus, we have not issued securities that do not represent our share capital.

The table below shows the changes in our share capital over the last three years.


Date	Type of operation	Prior Share Capital (€)		Premium (€)		Number of shares created		Total number of shares after issuance		Nominal value (€)		Share capital after transaction (€)		Issue price per share (€)
20/01/2023	Exercise of BCE-2014-4		223,131.85		0		18,400		22,331,585		0.01		223,315.85		0.01
01/03/2023	Capital increase through issue of new shares		223,315.85		129,800,000		20,000,000		42,331,585		0.01		423,315.85		6.50
10/05/2023	Exercise of BSA-2014-3		423,315.85		0		16,400		42,347,985		0.01		423,479.85		0.01
06/06/2023	Exercise of BSA-2018-KREOS-A		423,479.85		488,786.40		67,887		42,415,872		0.01		424,158.72		7.21
06/06/2023	Exercise of BSA-2018-KREOS-b		424,158.72		338,830.24		31,696		42,447,568		0.01		424,475.68		10.70
19/06/2023	Exercise of BCE-2014-2		424,475.68		0		100,000		42,547,568		0.01		425,475.68		0.01
12/09/2023	Exercise of BSA-2014-3		425,475.68		0		16,400		42,563,968		0.01		425,639.68		0.01
14/09/2023	Exercise of BSA-2014-3		425,639.68		0		16,400		42,580,368		0.01		425,803.68		0.01
24/10/2023	Capital increase through issue of new shares		425,803.68		223,173,990		20,325,500		62,905,868		0.01		629,058.68		10.99
20/11/2023	Exercise of BSA-2014-5		629,058.68		0		22,950		62,928,818		0.01		629,288.18		0.01
22/04/2024	Exercise of BCE-2017-5		629,288.18		11,130		1,000		62,929,818		0.01		629,298.18		11.14
23/04/2024	Exercise of BCE-2017-5		629,298.18		11,130		1,000		62,930,818		0.01		629,308.18		11.14


Date	Type of operation	Prior Share Capital (€)		Premium (€)		Number of shares created		Total number of shares after issuance		Nominal value (€)		Share capital after transaction (€)		Issue price per share (€)
11/06/2024	Exercise of BCE-2017-5		629,308.18		11,130		1,000		62,931,818		0.01		629,318.18		11.14
13/06/2024	Exercise of BCE-2017-5		629,318.18		11,130		1,000		62,932,818		0.01		629,328.18		11.14
11/07/2024	Definitive allocation of free shares		629,328.18		0		344,107		63,276,925		0.01		632,769.25		0.00
05/09/2024	Definitive allocation of free shares		632,769.25		0		17,728		63,294,653		0.01		632,946.53		0.00
13/11/2024	Definitive allocation of free shares		632,946.53		0		53,184		63,347,837		0.01		633,478.37		0.00
23/07/2025	Exercise of BCE-2018-5		634,719.33		7,320.00		1,000		63,472,933		0.01		634,729.33		7.33
24/07/2025	Exercise of BCE-2016-1		634,729.33		25,997.57		3,499		63,476,432		0.01		634,764.32		7.44
25/07/2025	Exercise of BCE-2018-1		634,764.32		14,767.50		1,650		63,478,082		0.01		634,780.82		8.96
28/07/2025	Capital increase through issue of new shares		634,780.82		637,228,064.00		11,679,400		75,157,482		0.01		751,574.82		54.57
29/07/2025	Exercise of BCE-2018-5		751,574.82		7,320.00		1,000		75,158,482		0.01		751,584.82		7.33
29/07/2025	Conversion of convertible bonds		751,584.82		9,371,047.91		394,447		75,552,929		0.01		755,529.29		23.77
30/07/2025	Exercise of BCE-2016-1		755,529.29		22,290,00		3,000		75,555,929		0.01		755,559.29		7.44
30/07/2025	Exercise of BCE-2016-1		755,559.29		26,850.00.00		3,000		75,558,929		0.01		755,589.29		8.96
01/08/2025	Definitive allocation of free shares		755,589.29		0.00		27,728		75,586,657		0.01		755,866.57		0.00
04/08/2025	Exercise of BCE-2018-1		755,866.57		17,300.00		2,000		75,588,657		0.01		755,886.57		8.96
05/08/2025	Exercise of BCE-2016-1		755,886.57		4,829.50		650		75,589,307		0.01		755,893.07		7.44
06/08/2025	Exercise of BCE-2018-1		755,893.07		16,110.0		1,800		75,591,107		0.01		755,911.07		8.96
06/08/2025	Exercise of BCE-2016-1		755,911.07		29,712.57		3,999		75,595,106		0.01		755,951.06		7.44
07/08/2025	Exercise of BCE-2016-1		755,951.06		11,137.57		1,499		75,596,605		0.01		755,966.05		7.44
05/08/2025	Conversion of convertible bonds		755,966.05		12,494,729.38		525,930		76,122,535		0.01		761,225.35		23.76
08/08/2025	Conversion of convertible bonds		761,225.35		16,658,807.54		785,389		76,907,924		0.01		769,079.24		21.21
08/08/2025	Exercise of BSA (Kreos)		769,079.24		2,665,728.23		95,742		77,003,666		0.01		770,036.66		18.67
08/08/2025	Exercise of BSA (Kreos)		770,036.66		2,664,564.29		223,509.00		77,227,175,00		0.01		772,271.75		9.86
28/08/2025	Exercise of BSA (Claret)		772,985.74		1,331,840.08		135,263		77,433,837		0.01		774,338.37		9.86
04/09/2025	Definitive allocation of free shares		774,338.37		0.00		17,728		77,451,565		0.01		774,515.65		0.00
04/09/2025	Exercise of BCE-2016-1		774,515.65		1,107.07		149		77,451,714		0.01		774,517.14		7.44
08/09/2025	Exercise of BCE-2016-1		774,517.14		7,430.00		1,000		77,452,714		0.01		774,527.14		7.44
28/09/2025	Definitive allocation of free shares		774,527.14		0.00		377,353		77,830,067		0.01		778,300.67		0.00
02/10/2025	Exercise of BSA-2015-12		778,300.67		291,592.00		16,400		77,846,467		0.01		778,464.67		17.79
23/10/2025	Exercise of BSA-2017-1		778,464.67		189,584.00		16,400		77,862,867		0.01		778,628.67		11.57
23/10/2025	Exercise of BCE-2016-1		778,628.67		37,150.00		5,000		77,867,867		0.01		778,678.67		7.44
12/11/2025	Exercise of BCE-2018-1		778,678.67		8,860.50		990		77,868,857		0.01		778,688.57		8.96
13/11/2025	Definitive allocation of free shares		778,688.57		0.00		35,456		77,904,313		0.01		779,043.13		0.00
17/11/2025	Exercise of BSA-2015-11		779,043.13		1,723,308.72		96,924		78,001,237		0.01		780,012.37		17.79
28/11/2025	Exercise of BSA-2024-1		780,012.37		63,656.67		4,863		78,006,100		0.01		780,061.00		13.10
01/12/2025	Definitive allocation of free shares		780,061.00		0.00		27,625		78,033,725		0.01		780,337.25		0.00
02/12/2025	Conversion of convertible bonds (Claret)		780,337.25		8,329,406.05		392,695		78,426,420		0.01		784,264.20		21.22
11/12/2025	Definitive allocation of free shares		784,264.20		0.00		17,728		78,444,148		0.01		784,441.48		0.00
16/12/2025	Exercise of BCE-2017-1		784,441.48		212,536.94		33,313		78,477,461		0.01		784,774.61		6.39
17/12/2025	Exercise of BCE-2017-5		784,774.61		187,462.59		16,843		78,494,304		0.01		784,943.04		11.14
17/12/2025	Exercise of BCE-2018-4		784,943.04		61,649.04		8,422		78,502,726		0.01		785,027.26		7.33
19/12/2025	Exercise of BCE-2017-4		785,027.26		374,925.18		33,686		78,536,412		0.01		785,364.12		11.14
12/01/2026	Exercise of BCE-2018-1		785,364.12		22,733.00		2,540		78,538,952		0.01		785,389.52		8.96
01/02/2026	Definitive allocation of free shares		785,389.52		0.00		628,480		79,167,432		0.01