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[Form 4] Seres Therapeutics, Inc. Insider Trading Activity

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
4

Rhea-AI Filing Summary

Seres Therapeutics director Eric D. Shaff reported routine stock transactions tied to vesting of restricted stock units. On May 18, 2026, he sold 259 shares of common stock at $7.53 per share in an open-market sale executed under a pre-arranged Rule 10b5-1 instruction adopted to cover taxes from RSU vesting.

On May 15, 2026, Shaff exercised derivative awards to acquire 722 shares of common stock at a conversion price of $0.00 as RSUs vested and settled. Following these transactions, he directly holds 12,040 shares of common stock, and additional RSUs remain outstanding that continue to vest in quarterly installments.

Positive

  • None.

Negative

  • None.

Insights

Routine RSU vesting with small tax-related sale under a 10b5-1 plan.

Director Eric D. Shaff converted restricted stock units into 722 shares of Seres Therapeutics common stock and sold 259 shares at $7.53. The filing states the sale was made under a Rule 10b5-1 instruction specifically to cover tax obligations from RSU vesting.

This pattern—RSU vesting plus a modest sale for taxes—is typical for equity compensation and carries limited informational value about the insider’s outlook. After the sale, Shaff still directly owns 12,040 shares and continues to hold restricted stock units that vest in quarterly installments, indicating an ongoing equity position.

Insider Shaff Eric D.
Role null
Sold 259 shs ($2K)
Type Security Shares Price Value
Sale Common Stock 259 $7.53 $2K
Exercise Restricted Stock Units 391 $0.00 --
Exercise Restricted Stock Units 331 $0.00 --
Exercise Common Stock 722 $0.00 --
Holdings After Transaction: Common Stock — 12,040 shares (Direct, null); Restricted Stock Units — 1,173 shares (Direct, null)
Footnotes (1)
  1. Each restricted stock unit represents a contingent right to receive one share of Issuer common stock. 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. 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. 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.
Form 4 Insider Transactions: What Each Field Means →
SEC Form 4
FORM 4UNITED 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)
XDirector10% Owner
Officer (give title below)Other (specify below)
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
05/15/2026		6. Individual or Joint/Group Filing (Check Applicable Line)
XForm 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)
CodeVAmount(A) or (D)Price
Common Stock05/15/2026M722A(1)12,299D
Common Stock05/18/2026S(2)259D$7.5312,040D
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)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Restricted Stock Units(1)05/15/2026M391 (3) (3)Common Stock391$01,173D
Restricted Stock Units(1)05/15/2026M331 (4) (4)Common Stock331$02,325D
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. Shaff05/19/2026
** Signature of Reporting PersonDate
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)

Source: View Original Filing on SEC EDGAR

FAQ

What insider transactions did Eric D. Shaff report for Seres Therapeutics (MCRB)?

Eric D. Shaff reported exercising restricted stock units into 722 common shares and selling 259 shares at $7.53 each. These transactions reflect RSU vesting activity combined with a small open-market sale disclosed in a Form 4 filing.

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

He sold 259 shares of Seres Therapeutics common stock at $7.53 per share. The transaction was coded as an open-market sale and was executed under a pre-arranged Rule 10b5-1 instruction to help cover taxes from restricted stock unit vesting.

How many Seres Therapeutics shares does Eric D. Shaff hold after this Form 4?

Following the reported transactions, Eric D. Shaff directly holds 12,040 shares of Seres Therapeutics common stock. In addition, he continues to hold restricted stock units that vest and settle in scheduled quarterly installments according to the award terms.

Were Eric D. Shaff’s Seres Therapeutics share sales part of a Rule 10b5-1 plan?

Yes. The Form 4 footnotes state the sales were effected under a Rule 10b5-1 instruction adopted on March 2, 2023. The instruction was used solely to cover taxes associated with the vesting of restricted stock units, indicating a pre-planned, routine liquidity event.

What is the nature of the restricted stock units reported by Eric D. Shaff at Seres Therapeutics?

Each restricted stock unit represents a contingent right to receive one share of Seres Therapeutics common stock. The RSUs vest 25% on a specified February 15 date, with the remaining portions vesting and settling in 12 equal quarterly installments thereafter, with no expiration date.

Does this Seres Therapeutics Form 4 indicate significant selling by Eric D. Shaff?

The filing shows a sale of 259 shares versus 722 shares acquired through restricted stock unit vesting. The sale was specifically to cover tax obligations, and Shaff continues to directly hold 12,040 common shares plus additional unexpired restricted stock units.