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

Rhea-AI Filing Summary

Eric D. Shaff, a director of Seres Therapeutics (MCRB), received and reported the settlement of restricted stock units and a small sale of common stock under a 10b5-1 plan. On 08/15/2025 he had two non-derivative acquisitions: 391 and 333 shares issued on settlement of restricted stock units, increasing his beneficial ownership to 10,493 and 10,826 shares respectively. On 08/18/2025 he sold 217 shares at $16.65 each, which the form states were executed under a Rule 10b5-1 instruction adopted to cover taxes related to RSU vesting. The RSUs vest in scheduled installments (25% earlier vesting followed by quarterly vesting) and have no expiration date.

Insights

Securities Compliance Analyst

TL;DR: Routine RSU vesting and a tax-cover sale executed under a pre-existing 10b5-1 plan; disclosure aligns with Section 16 requirements.

The transactions are standard Section 16 reporting events: vesting/settlement of restricted stock units and a small sale to cover tax obligations. The filer checked the box indicating the sale was pursuant to a 10b5-1 plan adopted March 2, 2023, which supports an affirmative defense to insider trading claims. Reported post-transaction beneficial ownership levels are modest in size and consistent with scheduled compensation vesting rather than opportunistic trading. No material corporate events, unusual sales, or large departures from prior ownership are reported.

Corporate Governance Specialist

TL;DR: Governance-normal disclosure: director received compensation shares and used an automated plan for a small tax-related sale.

The Form 4 documents standard equity compensation mechanics: two RSU settlements on 08/15/2025 and a subsequent small disposition on 08/18/2025 at $16.65 per share. The filing notes the RSUs vest 25% initially with the remainder in 12 equal quarterly installments and that the awards have no expiration date. The attachment of an executed 10b5-1 instruction provides procedural transparency; the dollar value and quantity sold are immaterial relative to the company scale and consistent with tax-withholding practices for executives and directors.

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
Estimated average burden
hours per response:			0.5

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)
08/15/2025

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	08/15/2025		M		391	A	(1)	10,493	D
Common Stock	08/15/2025		M		333	A	(1)	10,826	D
Common Stock	08/18/2025		S(2)		217	D	$16.65	10,609	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)	08/15/2025		M			391	(3)	(3)	Common Stock	391	$0	2,344	D
Restricted Stock Units	(1)	08/15/2025		M			333	(4)	(4)	Common Stock	333	$0	3,320	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	08/19/2025
	** 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 transactions did Eric D. Shaff report on the Form 4 for MCRB?

He reported settlement of 391 and 333 restricted stock units on 08/15/2025 and a sale of 217 shares on 08/18/2025 at $16.65 per share.

Why were shares sold by the reporting person in this Form 4?

The sale was effected pursuant to a Rule 10b5-1 instruction adopted on March 2, 2023, and the form states it was intended solely to cover taxes related to RSU vesting.

How did the reported transactions affect Eric D. Shaff's beneficial ownership of MCRB common stock?

Following the RSU settlements and the sale, the filing shows beneficial ownership amounts of 10,493 shares and 10,609 shares after the transactions as reported in the form tables.

What are the vesting terms described for the restricted stock units?

The RSUs vested 25% on earlier vesting dates and the remainder vest and settle in 12 equal quarterly installments; the RSUs have no expiration date.