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

Rhea-AI Filing Summary

Seres Therapeutics, Inc. director reports RSU vesting and small share sale. On 11/15/2025, the reporting person exercised restricted stock units that converted into 390 and 331 shares of common stock, increasing direct holdings and reflecting ongoing equity compensation. On the same date, 217 shares of common stock were sold at $17.30 per share under a pre-arranged Rule 10b5-1 trading instruction intended solely to cover taxes tied to the RSU vesting. After these transactions, the director directly beneficially owned 11,113 shares of common stock, along with 1,954 and 2,989 restricted stock units that vest in scheduled quarterly installments.

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

OMB APPROVAL

OMB Number:			3235-0287
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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)
11/15/2025

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	11/15/2025		M		390	A	(1)	10,999	D
Common Stock	11/15/2025		M		331	A	(1)	11,330	D
Common Stock	11/15/2025		S(2)		217	D	$17.3	11,113	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)	11/15/2025		M			390	(3)	(3)	Common Stock	390	$0	1,954	D
Restricted Stock Units	(1)	11/15/2025		M			331	(4)	(4)	Common Stock	331	$0	2,989	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	11/18/2025
	** 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 4 (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.

FAQ

What insider transaction did Seres Therapeutics (MCRB) report on this Form 4?

The filing discloses that a director of Seres Therapeutics, Inc. had restricted stock units convert into common stock and also sold a small number of shares on 11/15/2025.

How many Seres Therapeutics (MCRB) shares were sold and at what price?

The director sold 217 shares of Seres Therapeutics common stock at a price of $17.30 per share.

Were the Seres Therapeutics (MCRB) share sales under a Rule 10b5-1 plan?

Yes. The filing states the sales were made under a Rule 10b5-1 instruction adopted on March 2, 2023, intended solely to cover taxes related to restricted stock unit vesting.

How many Seres Therapeutics (MCRB) restricted stock units vested in this transaction?

Restricted stock units that converted into 390 shares and 331 shares of common stock vested and settled on 11/15/2025.

What is the director’s Seres Therapeutics (MCRB) share ownership after the Form 4 transactions?

Following the reported transactions, the director beneficially owned 11,113 shares of common stock, plus 1,954 and 2,989 restricted stock units scheduled to vest over time.

What is the vesting schedule for the Seres Therapeutics (MCRB) restricted stock units?

For one RSU grant, 25% vested on February 15, 2024, with the remainder vesting in 12 equal quarterly installments. For the other, 25% vested on February 15, 2025, with the remainder also vesting in 12 equal quarterly installments. The units have no expiration date.