SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 2)

SAB Biotherapeutics, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

78397T202

(CUSIP Number)

Peter Kolchinsky
RA Capital Management, L.P., 200 Berkeley Street, 18th Floor
Boston, MA, 02116
617.778.2500

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

03/19/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. Checkbox not checked

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP Number(s):

78397T202

Name of reporting person

RA Capital Management, L.P.

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,311,225.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,311,225.00

Aggregate amount beneficially owned by each reporting person

7,311,225.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

9.9 %

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13D

CUSIP Number(s):

78397T202

Name of reporting person

Peter Kolchinsky

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,311,225.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,311,225.00

Aggregate amount beneficially owned by each reporting person

7,311,225.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

9.9 %

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s):

78397T202

Name of reporting person

Rajeev Shah

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,311,225.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,311,225.00

Aggregate amount beneficially owned by each reporting person

7,311,225.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

9.9 %

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s):

78397T202

Name of reporting person

RA Capital Healthcare Fund, L.P.

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,311,225.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,311,225.00

Aggregate amount beneficially owned by each reporting person

7,311,225.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

9.9 %

Type of Reporting Person (See Instructions)

SCHEDULE 13D

Item 1.

Security and Issuer

(a)

Title of Class of Securities:

Common Stock, $0.0001 par value per share

(b)

Name of Issuer:

SAB Biotherapeutics, Inc.

(c)

Address of Issuer's Principal Executive Offices:

777 W 41st St., Suite 401, Miami Beach, FLORIDA , 33140.

Item 1 Comment:

This Amendment No. 2 (this "Amendment No. 2" or this "Schedule 13D/A") amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission (the "SEC") on October 3, 2025 and amended on March 11, 2026 (as amended, the "Statement") by the Reporting Persons. Unless otherwise defined herein, capitalized terms used in this Amendment No. 2 shall have the meanings ascribed to them in the Statement. Unless amended or supplemented below, the information in the Statement remains unchanged.

Item 2.

Identity and Background

(a)

This Schedule 13D/A is being filed on behalf of RA Capital Management, L.P. ("RA Capital"), Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. (the "Fund"). RA Capital, Dr. Kolchinsky, Mr. Shah and the Fund are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this Schedule 13D/A jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934, as amended, (the "Act") is attached hereto as Exhibit 99.1. The Fund directly holds (i) 4,401,500 shares of common stock; (ii) Series B preferred stock ("Preferred Stock") convertible into up to 12,738,500 shares of common stock at a conversion ratio of 100 shares of common stock per share of Preferred Stock; (iii) Preferred Stock purchase warrants (the "Release Date Warrants") exercisable for up to 85,700 shares of Preferred Stock; (iv) Preferred Stock purchase warrants (the "Enrollment Date Warrants" and, together with the Release Date Warrants, the "Preferred Warrants") exercisable for up to 171,400 shares of Preferred Stock; and (v) pre-funded warrants (the "Pre-Funded Warrants") exercisable for up to 2,753,246 shares of common stock. Each of the Preferred Stock and the Pre-Funded Warrants contains a provision (the "Beneficial Ownership Blockers") which precludes conversion of the Preferred Stock and/or exercise of the Pre-Funded Warrants to the extent that, following conversion and/or exercise, the Fund, together with its affiliates and other attribution parties, would own more than 9.99% of the common stock outstanding. The Fund is currently prohibited from converting the Preferred Stock and/or exercising the Pre-Funded Warrants by virtue of the Beneficial Ownership Blockers to the extent that such exercise would result in the Reporting Persons' beneficial ownership of more than 7,311,225 shares of common stock. The Fund may decrease or increase the maximum percentage by written notice to the Issuer from time to time to any other percentage not in excess of 19.99%, provided that any increase in the maximum percentage will not be effective until the sixty-first (61st) day after such notice is delivered to the Issuer. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund. The Fund has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because the Fund has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, the Fund disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13D/A other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13D/A shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.

(b)

The address of the principal business office of each of the Reporting Persons is 200 Berkeley Street, 18th Floor, Boston, MA 02116.

(c)

The Fund is a private investment vehicle. RA Capital provides investment management services to the Fund. The principal occupation of each of Dr. Kolchinsky and Mr. Shah is investment management.

(d)

During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)

During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree of final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)

See Item 6 of the cover pages.

Item 3.

Source and Amount of Funds or Other Consideration

Item 3 of the Statement is hereby amended and supplemented as follows: On March 19, 2026, the Fund purchased Pre-Funded Warrants to purchase 2,753,246 shares of common stock at a price of $3.8499 per warrant share, from the underwriters of the Issuer's public offering (the "March 2026 Offering"). The aggregate purchase price for the Pre-Funded Warrants acquired by the Fund in the March 2026 Offering was $10,599,721.78, which was funded by the working capital of the Fund.

Item 5.

Interest in Securities of the Issuer

(a)

Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon the sum of: (i) 50,951,037 shares of common stock outstanding as of March 2, 2026, as reported in the Issuer's Annual Report on Form 10-K filed with the SEC on March 9, 2026 and (ii) 19,324,677shares of common stock issued in the March 2026 Offering, and giving effect to the Preferred Stock, the Preferred Warrants and the Pre-Funded Warrants, to the extent convertible and/or exercisable within 60 days hereof, as referenced herein. Due to field limitations of the EDGAR filing system, the percentage listed in Row 13 of each of the cover pages has been rounded down to 9.9%.

(b)

Rows 7 through 10 of each Reporting Person's cover page to this Schedule 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.

(c)

Except as set forth herein, none of the Reporting Persons has effected any transactions with respect to the securities of the Issuer since the most recent amendment to this Schedule 13D/A.

(d)

No person (other than the Reporting Persons) is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities subject to this Schedule 13D/A.

(e)

Not applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer

Item 6 of the Statement is hereby amended and supplemented as follows: Pre-Funded Warrants Each Pre-Funded Warrant has an exercise price of $0.0001 per share of common stock, is immediately exercisable and does not expire. Under the terms of the Pre-Funded Warrants, the Issuer may not effect the exercise of any Pre-Funded Warrant, and the Fund will not be entitled to exercise any portion of any Pre-Funded Warrant, which, upon giving effect to such exercise, would cause the Fund (together with its affiliates) to own more than 9.99% of the number of shares of the common stock outstanding immediately after giving effect to such exercise, as such percentage ownership is determined in accordance with the terms of the Pre-Funded Warrants. The exercise price and the number of shares of common stock issuable upon exercise of each Pre-Funded Warrant are subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the common stock. In the event of certain fundamental transactions (as described in the Pre-Funded Warrants), a holder of Pre Funded Warrants will be entitled to receive, upon exercise of the Pre-Funded Warrants, the kind and amount of securities, cash or property that such holder would have received had they exercised in full the Pre-Funded Warrants immediately prior to such fundamental transaction without regard to any limitations on exercise contained in the Pre Funded Warrants. References to and the description of the Pre-Funded Warrants set forth above in this Item 6 do not purport to be complete and are qualified in their entirety by reference to the full text of the Form of Pre-Funded Warrant, which is attached hereto as Exhibit 99.2 and incorporated by reference herein.

Item 7.

Material to be Filed as Exhibits.

Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Reporting Persons' Schedule 13D filed with the SEC on October 3, 2025). Exhibit 99.2 Form of Pre-Funded Warrant (incorporated by reference to Exhibit 4.1 to the Issuer's Current Report on Form 8-K (File No. 001-39871) filed on March 19, 2026).

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

RA Capital Management, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By Peter Kolchinsky, Authorized Signatory
Date:	03/23/2026

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	03/23/2026

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	03/23/2026

RA Capital Healthcare Fund, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	03/23/2026

Amendment: SEC Form SCHEDULE 13D/A filed by SAB Biotherapeutics Inc.