Eric D. Shaff - 15 Aug 2026 Form 4 Insider Report for Seres Therapeutics, Inc. (MCRB)

Reporting relationship: Director
Issuer ticker: MCRB
Reported as of: 15 Aug 2026
Net transaction value: -$1,197
SEC form: 4
Accepted by SEC: 18 Aug 2026, 17:27:35 UTC
Prior SEC filing: 10 Jul 2026
Source filing: View source filing
Reporting owner signature: /s/ Thomas J. DesRosier, Attorney-in-Fact for Eric D. Shaff

Key filing fact

Eric D. Shaff filed Form 4 for Seres Therapeutics, Inc. (MCRB) on 18 Aug 2026.

Key facts

This page summarizes Eric D. Shaff's Form 4 filing for Seres Therapeutics, Inc. (MCRB).
4 reported transactions and 2 derivative rows are listed below.
Accepted by SEC: 18 Aug 2026, 17:27.

Change

Previous filing in this sequence was filed on 10 Jul 2026.
Current net transaction value: -$1,197.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001643734 Primary reporting owner

Shaff Eric D.

Relationship: Director
Address: C/O SERES THERAPEUTICS, INC., 101 CAMBRIDGE PARK DRIVE, CAMBRIDGE
Signature: /s/ Thomas J. DesRosier, Attorney-in-Fact for Eric D. Shaff
Signature date: 18 Aug 2026

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

MCRB transaction

Common Stock

Options Exercise

Transaction value
Shares: +722
Change %: +6%
Price
Shares after: 12,762
Date: 15 Aug 2026
Ownership: Direct
Footnotes: F1

MCRB transaction

Common Stock

Sale

Transaction value: $1,197
Shares: -263
Change %: -2.1%
Price: $4.55
Shares after: 12,499
Date: 17 Aug 2026
Ownership: Direct
Footnotes: F2

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

MCRB transaction Derivative

Restricted Stock Units

Options Exercise

Transaction value
Shares: -390
Change %: -33%
Price: $0.000000^*
Shares after: 783
Date: 15 Aug 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 390
Exercise price
Footnotes: F1, F3

MCRB transaction Derivative

Restricted Stock Units

Options Exercise

Transaction value
Shares: -332
Change %: -14%
Price: $0.000000^*
Shares after: 1,993
Date: 15 Aug 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 332
Exercise price
Footnotes: F1, F4

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 4 footnotes

Footnote F1

Each restricted stock unit represents a contingent right to receive one share of Issuer common stock.

Footnote 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.

Footnote 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.

Footnote 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.