[Form 4] Seres Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Seres Therapeutics director Eric D. Shaff reported several equity transactions on February 15, 2026 tied to his restricted stock units (RSUs). He exercised RSU-derived rights for a total of 723 shares of common stock, then sold 259 shares of common stock at $8.47 per share under a pre-arranged Rule 10b5-1 instruction, which the filing states was intended solely to cover taxes from RSU vesting. Following these moves, he directly held 11,577 shares of common stock, while his RSU awards continue to vest in scheduled quarterly installments.

Insights

Equity compensation and insider-trading analyst

Routine RSU vesting with a small tax-driven sale; neutral impact.

Eric D. Shaff, a director of Seres Therapeutics, exercised RSU-related rights into 723 shares of common stock and sold 259 shares at $8.47 on February 15, 2026. The filing describes the code M entries as exercises or conversions of derivative securities.

The open-market sale is reported under transaction code S and occurs pursuant to a Rule 10b5-1 instruction adopted on March 2, 2023, with the footnote stating it was intended solely to cover taxes related to RSU vesting. Such tax-cover transactions are common in equity compensation programs.

The net result is a modest reduction of 259 freely held shares while overall equity exposure remains meaningful, with 11,577 common shares directly owned after the sale and ongoing RSU vesting described in the schedule. From an investment thesis standpoint, these routine compensation-driven moves are best viewed as neutral rather than signaling a change in insider sentiment.

SEC Form 4

FORM 4

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

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

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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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Shaff Eric D.

(Last) (First) (Middle)

C/O SERES THERAPEUTICS, INC.

101 CAMBRIDGE PARK DRIVE

(Street)

CAMBRIDGE MA 02140

(City) (State) (Zip)

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

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

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

3. Date of Earliest Transaction (Month/Day/Year)
02/15/2026

4. 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 Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	02/15/2026		M		723	A	(1)	11,836	D
Common Stock	02/15/2026		S(2)		259	D	$8.47	11,577	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Units	(1)	02/15/2026		M			391	(3)	(3)	Common Stock	391	$0	1,564	D
Restricted Stock Units	(1)	02/15/2026		M			333	(4)	(4)	Common Stock	333	$0	2,656	D

Explanation of Responses:

1. Each restricted stock unit represents a contingent right to receive one share of Issuer common stock.

2. The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 instruction adopted by the reporting person on March 2, 2023, solely with the intent to cover taxes in connection with the vesting of the restricted stock units.

3. The restricted stock units vested and settled as to 25% of the restricted stock units on February 15, 2024. The remainder of the restricted stock units have vested and settled or will vest and settle in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

4. The restricted stock units vested and settled as to 25% of the restricted stock units on February 15, 2025. The remainder of the restricted stock units have vested and settled or will vest and settle in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

	/s/ Thomas J. DesRosier, attorney-in-fact for Eric D. Shaff	02/18/2026
	** Signature of Reporting Person	Date
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