Seres Therapeutics officer granted 22,500 options

Seres Therapeutics, Inc. reported that officer Marella Thorell received a grant of stock options covering 22,500 shares of the company’s stock.

Rhea-AI Filing Summary

Seres Therapeutics, Inc. reported that officer Marella Thorell received a grant of stock options covering 22,500 shares of the company’s stock. This is classified as a grant or award acquisition, not a market purchase or sale.

According to the vesting terms, 25% of the option shares will vest on March 2, 2027, with the remaining shares vesting in 12 equal quarterly installments after that date. Following this grant, Thorell’s directly held option position from this award totals 22,500 option shares.

Insider Trade Summary

Grant/Award: 22,500 shares

Grant/Award 1 txn

Insider Thorell Marella

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

What insider transaction did Seres Therapeutics (MCRB) report for Marella Thorell?

Seres Therapeutics reported that officer Marella Thorell received a grant of stock options for 22,500 shares. The transaction is coded as an acquisition award, meaning it is an equity grant rather than a market purchase or sale of existing shares.

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

The new stock option grant to Marella Thorell covers 22,500 shares of Seres Therapeutics common stock. This entire amount reflects options, not currently owned common shares, and represents Thorell’s total holdings from this particular award after the reported transaction.

What is the vesting schedule for Marella Thorell’s Seres Therapeutics (MCRB) options?

The option grant will vest as to 25% of the 22,500 shares on March 2, 2027. The remaining 75% will vest in 12 equal quarterly installments thereafter, creating a long-term, time-based vesting structure for this equity award.

Does the Seres Therapeutics (MCRB) Form 4 show any market buy or sell by Marella Thorell?

No market buy or sell is shown; the Form 4 reports a stock option grant coded as a grant or award acquisition. This means Thorell did not trade shares in the open market but received an option incentive tied to future vesting.

Is Marella Thorell’s ownership in Seres Therapeutics (MCRB) direct or indirect for this option grant?

For this option grant, ownership is reported as direct. The filing lists the ownership type as direct, with no footnote indicating that the options are held through a separate entity or that beneficial ownership is disclaimed.

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Accepted by SEC EDGAR 03/06/2026 - 04:33 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^*

Thorell Marella

(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 Financial Officer

	/s/ Thomas J. DesRosier, Attorney-in-Fact for Marella Thorell	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.