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

Rhea-AI Filing Summary

Teresa L. Young, EVP, Chief Commercial & Strategy Officer of Seres Therapeutics, Inc. (Ticker: MCRB), reported vesting and settlement of restricted stock units and a small sale of common stock in August 2025. On 08/15/2025 two tranches of restricted stock units were reported (133 and 97 RSUs) that represent contingent rights to receive shares; the filings show post-transaction beneficial ownership figures of 5,177 and 5,274 shares respectively. On 08/18/2025 the reporting person sold 59 shares at $16.65, executed under a Rule 10b5-1 instruction adopted March 5, 2023, described as intended solely to cover taxes relating to RSU vesting. The Form 4 is signed by an attorney-in-fact on 08/19/2025.

Positive

• RSU vesting disclosed, showing alignment of executive compensation with equity ownership
• Sale executed under a Rule 10b5-1 plan, indicating pre-planned, non-discretionary disposition to cover taxes

Negative

• Small reduction in direct holdings after the tax-cover sale (59 shares sold)

Insights

Securities Analyst

TL;DR: Small RSU settlements and a tax-cover sale under a 10b5-1 plan; not materially dilutive.

The reported activity shows executive compensation vesting (two RSU tranches) and a modest sale of 59 shares at $16.65 to cover tax obligations under a pre-existing Rule 10b5-1 plan. The transactions are routine for equity-based compensation and do not indicate a change in company guidance, financing or control. The net change in beneficial ownership is modest relative to the share counts reported, suggesting limited market impact.

Corporate Governance Expert

TL;DR: Proper disclosure of RSU vesting and planned sale demonstrates compliance with Section 16 reporting.

The Form 4 documents that the sales were effected pursuant to a 10b5-1 instruction and explains vesting schedules for the RSUs. The filing includes required detail on amounts acquired and disposed and is executed by an attorney-in-fact, which is common for insider reports. No indications of atypical governance or undisclosed compensation changes are present in the document.

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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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^*

Young Teresa L.

(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)	5,177	D
Common Stock	08/15/2025		M		97	A	(1)	5,274	D
Common Stock	08/18/2025		S(2)		59	D	$16.65	5,215	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			97	(4)	(4)	Common Stock	97	$0	976	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 5, 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:

EVP, Chief Commercial & Strategy Officer

	/s/ Thomas J. DesRosier, attorney-in-fact for Teresa L. Young	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

Who filed the Form 4 for MCRB?

Teresa L. Young, EVP, Chief Commercial & Strategy Officer, via attorney-in-fact Thomas J. DesRosier.

What transactions were reported on the Form 4 for MCRB?

Vesting and settlement of RSUs (133 and 97 units) on 08/15/2025 and a sale of 59 shares on 08/18/2025 at $16.65.

Why were shares sold on 08/18/2025 for MCRB?

The sale was effected pursuant to a Rule 10b5-1 instruction adopted March 5, 2023, described as intended solely to cover taxes related to RSU vesting.

How many shares did the reporting person own after the transactions?

The filing shows beneficial ownership figures of 5,177 and 5,274 after the reported acquisitions and 5,215 after the sale.

When were the transactions and when was the Form 4 signed?

Transactions occurred on 08/15/2025 and 08/18/2025; the Form 4 was signed by the attorney-in-fact on 08/19/2025.