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

Rhea-AI Filing Summary

Insider transactions at Seres Therapeutics (MCRB): Thomas J. DesRosier, a senior executive identified as Chief Legal Officer, EVP, Co‑CEO and Co‑President, reported restricted stock unit vesting and a small sale under a preexisting Rule 10b5‑1 plan. On 08/15/2025 DesRosier had 133 and 111 restricted stock units settle into common shares (total 244 shares) and beneficially owned 7,420 and 7,531 shares respectively after those settlements. On 08/18/2025 he sold 76 shares at $16.65 per share pursuant to the 10b5‑1 instruction to cover taxes related to vesting. The filings state the RSUs vest in scheduled quarterly installments and have no expiration.

Positive

• Transparent disclosure of RSU vesting schedule and settlements, including the number of units and that RSUs have no expiration
• Use of a documented Rule 10b5‑1 plan (adopted March 2, 2023) for the sale, indicating preplanned tax‑covering transactions

Negative

• Minor sale of 76 shares at $16.65 to cover taxes (small in absolute terms but a disposition nonetheless)

Insights

Securities Analyst

TL;DR: Routine insider vesting with a minor tax‑coverage sale under a 10b5‑1 plan; not material to valuation.

The Form 4 shows scheduled vesting of RSUs and a small sale of 76 shares at $16.65 executed under a 10b5‑1 plan adopted March 2, 2023 to cover taxes. The total share movements are modest relative to typical market capitalization and do not indicate an opportunistic disposition or change in control. This is a standard disclosure reflecting compensation settlement mechanics rather than a signal about company fundamentals.

Corporate Governance Expert

TL;DR: Disclosure aligns with good governance—insider used a documented 10b5‑1 plan and reported RSU vesting transparently.

DesRosier’s use of a preestablished Rule 10b5‑1 instruction for tax withholding and the explicit explanation of vesting schedules and settlement cadence are consistent with transparent insider trading practices. The filing includes role disclosures and signatures, meeting SEC Form 4 requirements. No unexplained amendments or large, atypical transactions appear.

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^*

DesRosier Thomas

(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)

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

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		133	A	(1)	7,420	D
Common Stock	08/15/2025		M		111	A	(1)	7,531	D
Common Stock	08/18/2025		S(2)		76	D	$16.65	7,455	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			133	(3)	(3)	Common Stock	133	$0	796	D
Restricted Stock Units	(1)	08/15/2025		M			111	(4)	(4)	Common Stock	111	$0	1,113	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.

Remarks:

Chief Legal Officer, EVP, Co-Chief Executive Officer, and Co-President

	/s/ Thomas J. DesRosier	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 did Thomas J. DesRosier report in the Form 4 for MCRB?

The Form 4 reports settlement of restricted stock units converting to common stock and a sale of 76 shares at $16.65 executed under a Rule 10b5‑1 plan to cover taxes.

How many restricted stock units vested or settled for DesRosier?

The filing shows 133 and 111 restricted stock units referenced, totaling 244 units that converted to common shares in the reported transactions.

Why was the 76‑share sale made according to the filing?

The sale was effected pursuant to a Rule 10b5‑1 instruction adopted on March 2, 2023, and was made solely to cover taxes related to the vesting of RSUs.

Do the restricted stock units expire?

No; the filing states the restricted stock units have no expiration date and vest in quarterly installments following initial 25% vesting events.

What roles does DesRosier hold at Seres Therapeutics as disclosed?

The filing lists DesRosier as Chief Legal Officer, EVP, Co‑Chief Executive Officer, and Co‑President.