Seres Therapeutics grants 22,500-share option to officer

DesRosier Thomas reported acquisition or exercise transactions in this Form 4 filing.

Rhea-AI Filing Summary

DesRosier Thomas reported acquisition or exercise transactions in this Form 4 filing.

Seres Therapeutics, Inc. reported that officer Thomas DesRosier received a grant of stock options covering 22,500 shares of the company’s stock. No cash was paid for this award, which is described as a “Stock Option (right to buy).”

According to the vesting terms, 25% of the option shares will vest on March 2, 2027. The remaining shares will then vest in 12 equal quarterly installments after that date, tying the award to continued service over several years.

Insider Trade Summary

Grant/Award: 22,500 shares

Grant/Award 1 txn

Insider DesRosier Thomas

Role See Remarks

Type	Security	Shares	Price	Value
Grant/Award	Stock Option (right to buy)	22,500	$0.00	$0.00

Holdings After Transaction: Stock Option (right to buy) — 22,500 contracts (Direct)

Footnotes (1)

1. F1. The option will vest as to 25% of the shares on March 2, 2027. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did Seres Therapeutics (MCRB) report for Thomas DesRosier?

Seres Therapeutics reported that officer Thomas DesRosier received a grant of stock options for 22,500 shares. The award is classified as a “Stock Option (right to buy)” and represents an acquisition of derivative securities rather than an open-market stock purchase.

How many shares are covered by the new stock option grant at Seres Therapeutics (MCRB)?

The new stock option grant to officer Thomas DesRosier covers 22,500 shares of Seres Therapeutics common stock. These options increase his derivative holdings to a total of 22,500 option shares following the reported transaction on the stated grant date.

When do the new Seres Therapeutics (MCRB) options granted to Thomas DesRosier start vesting?

The options begin vesting on March 2, 2027, when 25% of the shares become vested. This initial cliff vesting date marks the first point at which a portion of the 22,500 granted option shares becomes exercisable under the award’s terms.

What is the vesting schedule for the 22,500-share option grant at Seres Therapeutics (MCRB)?

The option vests 25% of the shares on March 2, 2027. The remaining 75% then vests in 12 equal quarterly installments, spreading vesting over three years after the initial cliff, subject to the applicable continued service conditions.

Did Thomas DesRosier pay a purchase price for the Seres Therapeutics (MCRB) option grant?

No purchase price was paid for this grant; the transaction price per option share is reported as 0.0000. This reflects that it is a compensatory stock option award, not an open-market purchase of existing common stock shares.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 03/06/2026 - 04:31 PM Learn about SEC filing dates

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).

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)
03/04/2026

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

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
Stock Option (right to buy)	$9.13	03/04/2026		A		22,500		(1)	03/03/2036	Common Stock	22,500	$0	22,500	D

Explanation of Responses:

1. The option will vest as to 25% of the shares on March 2, 2027. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

Remarks:

EVP and Chief Legal Officer

	/s/ Thomas J. DesRosier	03/06/2026
	** 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.