SEC FORM 3

SEC FORM 3 SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Brady Kelly

(Last)

(First)

(Middle)

C/O SERES THERAPEUTICS, INC.

101 CAMBRIDGE PARK DRIVE

(Street)

CAMBRIDGE

02140

(City)

(State)

(Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
03/02/2026

3. Issuer Name and Ticker or Trading Symbol
Seres Therapeutics, Inc. [ MCRB ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	See Remarks

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	8,441	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
1. Title of Derivative Security (Instr. 4)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
Stock Option (right to buy)	⁽¹⁾	02/13/2034	Common Stock	2,925	$22	D
Stock Option (right to buy)	⁽²⁾	02/06/2035	Common Stock	11,700	$15.64	D
Stock Option (right to buy)	⁽³⁾	02/11/2034	Common Stock	2,000	$23	D
Stock Option (right to buy)	⁽³⁾	02/11/2034	Common Stock	869	$23	D
Stock Option (right to buy)	⁽³⁾	02/11/2034	Common Stock	812	$23	D
Stock Option (right to buy)	⁽³⁾	02/11/2034	Common Stock	2,343	$23	D
Stock Option (right to buy)	⁽⁴⁾	02/11/2034	Common Stock	1,430	$23	D
Restricted Stock Units	⁽⁵⁾	⁽⁵⁾	Common Stock	358	$0	D
Restricted Stock Units	⁽⁶⁾	⁽⁶⁾	Common Stock	730	$0	D

Explanation of Responses:

1. The options were granted on February 14, 2024. The option vested as to 25% of the shares on February 14, 2025. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

2. The options were granted on February 7, 2025. The option vested as to 25% of the shares on February 7, 2026. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

3. The stock options are fully vested.

4. The options were granted on February 12, 2024. The option vested as to 25% of the shares on February 3, 2024. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

5. The restricted stock units were granted on February 3, 2023. The restricted stock units vested as to 25% of the shares on February 15, 2024. The remainder of the shares will vest in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

6. The restricted stock units were granted on February 14, 2024. The restricted stock units vested as to 25% of the shares on February 15, 2025. The remainder of the shares will vest in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

Remarks:

EVP and Chief Operating Officer Exhibit 24 - Power of Attorney.

	/s/ Thomas J. DesRosier, Attorney-in-Fact for Kelly M. Brady	03/11/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

New insider Brady Kelly claimed ownership of 8,441 shares (SEC Form 3)