Seres director sells 263 shares after RSU vesting

Seres Therapeutics, Inc. (MCRB) director Eric D. Shaff reported equity award activity and a small share sale.

Rhea-AI Filing Summary

Seres Therapeutics, Inc. (MCRB) director Eric D. Shaff reported equity award activity and a small share sale. On August 15, 2026, restricted stock units covering 722 shares of common stock vested and settled into common shares. On August 17, 2026, he sold 263 common shares at $4.55 per share pursuant to a pre-arranged Rule 10b5-1 trading instruction solely to cover taxes related to the RSU vesting.

Insider Trade Summary 10b5-1

Exercise and sale activity reported; no spread calculated

Exercise and Sale 4 txns

Insider Shaff Eric D.

Role Director

Sold 263 shs ($1K)

Approx. gross sale proceeds $1K

Type	Security	Shares	Price	Value
Sale	Common Stock F2	263	$4.55	$1K
Exercise	Restricted Stock Units F1, F3	390	$0.00	$0.00
Exercise	Restricted Stock Units F1, F4	332	$0.00	$0.00
Exercise	Common Stock F1	722	--	--

Holdings After Transaction: Restricted Stock Units — 2,776 contracts (Direct); Common Stock — 12,499 shares (Direct)

Footnotes (4)

1. F1. Each restricted stock unit represents a contingent right to receive one share of Issuer common stock.
2. F2. 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. F3. 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. F4. 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.

Key Figures

Shares sold: 263 shares Sale price: $4.55 per share RSUs converted to common stock: 722 shares +3 more

6 metrics

Shares sold 263 shares Common stock sale on August 17, 2026

Sale price $4.55 per share Price for 263-share sale on August 17, 2026

RSUs converted to common stock 722 shares RSUs vesting and settling into common stock on August 15, 2026

First RSU tranche 390 RSUs RSUs converting into common stock from grant with 2024 vesting start

Second RSU tranche 332 RSUs RSUs converting into common stock from grant with 2025 vesting start

Rule 10b5-1 adoption date March 2, 2023 Date of trading instruction used for August 17, 2026 sale

Key Terms

Restricted Stock Units, Rule 10b5-1, quarterly installments, contingent right

4 terms

Restricted Stock Units financial

"The restricted stock units vested and settled as to 25% of the restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

Rule 10b5-1 regulatory

"The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 instruction"

Rule 10b5-1 is a regulation that allows company insiders to buy or sell their shares at predetermined times, even if they have access to non-public information. It acts like setting a schedule in advance for transactions, helping prevent accusations of unfair trading. This rule provides a way for insiders to plan trades transparently, giving investors confidence that these transactions are not based on hidden information.

quarterly installments financial

"will vest and settle in 12 equal quarterly installments thereafter"

contingent right financial

"Each restricted stock unit represents a contingent right to receive one share"

FAQ

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

What insider transactions did MCRB director Eric D. Shaff report on this Form 4?

Eric D. Shaff reported RSU vesting into 722 shares of Seres Therapeutics common stock on August 15, 2026, and a subsequent sale of 263 shares on August 17, 2026, at $4.55 per share under a Rule 10b5-1 instruction.

How many Seres Therapeutics (MCRB) shares did Eric D. Shaff sell and at what price?

Eric D. Shaff sold 263 shares of Seres Therapeutics common stock at $4.55 per share on August 17, 2026. The filing describes this as a sale in the open market or a private transaction.

Were Eric D. Shaff’s MCRB share sales made under a Rule 10b5-1 trading plan?

Yes. The filing states the sales were effected pursuant to a Rule 10b5-1 instruction adopted on March 2, 2023. The footnote explains the instruction was established solely to cover taxes in connection with the vesting of restricted stock units.

How many Seres Therapeutics (MCRB) restricted stock units vested for Eric D. Shaff?

Restricted stock units covering 722 shares of Seres Therapeutics common stock vested and settled on August 15, 2026. This consists of 390 RSUs from one grant and 332 RSUs from another, each convertible into one share of common stock.

What are the vesting schedules of Eric D. Shaff’s RSUs reported for MCRB?

One RSU grant vested 25% on February 15, 2024 and the rest in 12 equal quarterly installments afterward. Another vested 25% on February 15, 2025 with the remainder also in 12 equal quarterly installments; both have no expiration date.

Did the Form 4 for MCRB indicate remaining derivative positions for Eric D. Shaff?

The Form 4 transaction data show two RSU exercises totaling 722 shares and no remaining derivative positions listed in the derivative summary. The filing does not list additional outstanding options or RSUs within this specific report.

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

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Available on EDGAR 08/18/2026 - 05:28 PM Accepted by SEC EDGAR 08/18/2026 - 05:27 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).

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^*

Shaff Eric D.

(Last) (First) (Middle)

C/O SERES THERAPEUTICS, INC.

101 CAMBRIDGE PARK DRIVE

(Street)

CAMBRIDGE MASSACHUSETTS 02140

(City) (State) (Zip)

UNITED STATES

(Country)

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

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/15/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

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	08/15/2026		M		722	A	(1)	12,762	D
Common Stock	08/17/2026		S(2)		263	D	$4.55	12,499	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)	08/15/2026		M			390	(3)	(3)	Common Stock	390	$0	783	D
Restricted Stock Units	(1)	08/15/2026		M			332	(4)	(4)	Common Stock	332	$0	1,993	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.

	/s/ Thomas J. DesRosier, Attorney-in-Fact for Eric D. Shaff	08/18/2026
	** 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.
* Form 4: SEC 1474 (03-26)