Seres Therapeutics (MCRB) officer Brady Kelly reports stock holdings

Rhea-AI Filing Summary

Seres Therapeutics insider Brady Kelly has filed an initial ownership report showing existing equity holdings in the company. The filing lists several stock options to purchase Common Stock, including one covering 11,700 shares at an exercise price of 15.6400 per share expiring on February 6, 2035, plus additional options with exercise prices around 22.0000 to 23.0000 per share expiring in 2034. Kelly also holds Restricted Stock Units tied to 358 and 730 shares of Common Stock and directly owns 8,441 shares of Common Stock following the reported positions. The footnotes explain that these options and RSUs vest over time, with 25% already vested and the remainder scheduled to vest in 12 equal quarterly installments after the initial vesting dates.

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Brady Kelly

(Last) (First) (Middle)

C/O SERES THERAPEUTICS, INC.

101 CAMBRIDGE PARK DRIVE

(Street)

CAMBRIDGE MA 02140

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
03/02/2026

3. Issuer Name and Ticker or Trading Symbol
Seres Therapeutics, Inc. [ MCRB ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

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

5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	8,441	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (right to buy)	(1)	02/13/2034	Common Stock	2,925	$22	D
Stock Option (right to buy)	(2)	02/06/2035	Common Stock	11,700	$15.64	D
Stock Option (right to buy)	(3)	02/11/2034	Common Stock	2,000	$23	D
Stock Option (right to buy)	(3)	02/11/2034	Common Stock	869	$23	D
Stock Option (right to buy)	(3)	02/11/2034	Common Stock	812	$23	D
Stock Option (right to buy)	(3)	02/11/2034	Common Stock	2,343	$23	D
Stock Option (right to buy)	(4)	02/11/2034	Common Stock	1,430	$23	D
Restricted Stock Units	(5)	(5)	Common Stock	358	$0	D
Restricted Stock Units	(6)	(6)	Common Stock	730	$0	D

Explanation of Responses:

1. The options were granted on February 14, 2024. The option vested as to 25% of the shares on February 14, 2025. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

2. The options were granted on February 7, 2025. The option vested as to 25% of the shares on February 7, 2026. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

3. The stock options are fully vested.

4. The options were granted on February 12, 2024. The option vested as to 25% of the shares on February 3, 2024. The remainder of the shares will vest in 12 equal quarterly installments thereafter.

5. The restricted stock units were granted on February 3, 2023. The restricted stock units vested as to 25% of the shares on February 15, 2024. The remainder of the shares will vest in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

6. The restricted stock units were granted on February 14, 2024. The restricted stock units vested as to 25% of the shares on February 15, 2025. The remainder of the shares will vest in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date.

Remarks:

EVP and Chief Operating Officer Exhibit 24 - Power of Attorney.

	/s/ Thomas J. DesRosier, Attorney-in-Fact for Kelly M. Brady	03/11/2026
	** 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 5 (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 does the Seres Therapeutics (MCRB) Form 3 filing show for Brady Kelly?

The Form 3 shows Brady Kelly’s existing equity holdings in Seres Therapeutics, including several stock option grants, Restricted Stock Units, and 8,441 shares of Common Stock held directly after the reported positions, establishing a baseline for future insider transaction reporting.

How many Seres Therapeutics (MCRB) common shares does Brady Kelly hold directly?

Brady Kelly directly holds 8,441 shares of Seres Therapeutics Common Stock following the reported positions. This figure represents the current reported share ownership and serves as a reference point for any future purchases, sales, or equity awards that may be disclosed in later filings.

What stock options for Seres Therapeutics (MCRB) does Brady Kelly currently report?

Brady Kelly reports multiple stock options to buy Seres Therapeutics Common Stock, including an option over 11,700 underlying shares at an exercise price of $15.6400 per share expiring February 6, 2035, along with several additional options with exercise prices around $22–$23 expiring in 2034.

How do Brady Kelly’s Seres Therapeutics (MCRB) stock options vest over time?

The footnotes state that each option vested 25% on its first vesting date, with the remaining 75% scheduled to vest in 12 equal quarterly installments thereafter, creating a multi‑year vesting schedule that gradually delivers full vesting if Kelly remains with Seres Therapeutics.

What Restricted Stock Units in Seres Therapeutics (MCRB) does Brady Kelly hold?

Brady Kelly holds Restricted Stock Units tied to 358 and 730 shares of Seres Therapeutics Common Stock. These RSUs vested 25% on their initial vesting dates, with the remainder vesting in 12 equal quarterly installments, and they have no expiration date according to the footnotes.

Does the Seres Therapeutics (MCRB) Form 3 show Brady Kelly buying or selling shares?

The Form 3 functions as an initial ownership statement and lists holdings such as options, RSUs, and common shares. It does not report new open‑market purchases or sales, but instead establishes Kelly’s existing equity position for ongoing insider reporting requirements.