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

Seres Therapeutics (NASDAQ: MCRB) legal chief vests 245 shares, sells 82 under 10b5-1 plan

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

Rhea-AI Filing Summary

Seres Therapeutics, Inc. (MCRB) reported insider equity activity by EVP and Chief Legal Officer Thomas DesRosier. On August 15, 2026, a total of 245 shares of common stock were acquired upon settlement of restricted stock units, with two RSU awards of 133 and 112 units each converting into common shares, where each unit represents one share and has no expiration date. On August 17, 2026, 82 shares of common stock were sold at $4.55 per share in an open-market transaction made under a Rule 10b5-1 trading plan adopted on March 2, 2023, described as intended solely to cover taxes related to the RSU vesting.

Positive

  • None.

Negative

  • None.
Insider DesRosier Thomas
Role See Remarks
Sold 82 shs ($373.10)
Approx. gross sale proceeds $373.10
Type Security Shares Price Value
Sale Common Stock F2 82 $4.55 $373.10
Exercise Restricted Stock Units F1, F3 133 $0.00 $0.00
Exercise Restricted Stock Units F1, F4 112 $0.00 $0.00
Exercise Common Stock F1 245 -- --
Holdings After Transaction: Restricted Stock Units — 932 shares (Direct); Common Stock — 8,117 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.
Shares sold 82 shares Common stock sold on August 17, 2026
Sale price $4.55 per share Price for 82 common shares sold on August 17, 2026
RSU shares converted 245 shares Common shares acquired upon RSU settlement on August 15, 2026
First RSU tranche 133 units Restricted stock units converted into common stock on August 15, 2026
Second RSU tranche 112 units Restricted stock units converted into common stock on August 15, 2026
10b5-1 adoption date March 2, 2023 Adoption date of Rule 10b5-1 instruction covering the August 17, 2026 sale
Initial vesting percentages 25% each grant RSUs vest 25% on February 15, 2024 and 2025 for respective grants
Remaining vesting schedule 12 equal quarterly installments Post-initial 25% vesting schedule for each RSU grant
Restricted Stock Units financial
"Each restricted stock unit represents a contingent right to receive one share"
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
"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.
contingent right financial
"represents a contingent right to receive one share of Issuer common stock"
vesting financial
"cover taxes in connection with the vesting of the restricted stock units"
Vesting is the process by which you earn full ownership of something, like company stock or a retirement benefit, over time. It’s like earning the right to keep a gift piece by piece the longer you stay with a company, making sure employees stay committed before they receive all the benefits.
quarterly installments financial
"will vest and settle in 12 equal quarterly installments thereafter"

FAQ

What insider transactions did MCRB executive Thomas DesRosier report on this Form 4?
Thomas DesRosier reported 245 shares of Seres Therapeutics (MCRB) common stock acquired on August 15, 2026 via RSU settlement and a subsequent sale of 82 shares on August 17, 2026 at $4.55 per share.

How many Seres Therapeutics (MCRB) shares were sold and at what price?
DesRosier sold 82 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 under a Rule 10b5-1 plan.

Were the MCRB insider sales by Thomas DesRosier under a Rule 10b5-1 plan?
Yes. The sale of 82 shares on August 17, 2026 was effected pursuant to a Rule 10b5-1 instruction adopted on March 2, 2023, described as being solely to cover taxes related to restricted stock unit vesting.

What restricted stock unit activity did Seres Therapeutics (MCRB) disclose for Thomas DesRosier?
Two RSU awards for 133 and 112 units vested and settled into a total of 245 shares of MCRB common stock on August 15, 2026. Each RSU represents a contingent right to receive one share of Seres Therapeutics common stock.

What are the vesting terms for Thomas DesRosier’s RSUs at Seres Therapeutics (MCRB)?
One RSU grant vested 25% on February 15, 2024, and another 25% on February 15, 2025. For each grant, the remaining units vest and settle in 12 equal quarterly installments thereafter, and the RSUs have no expiration date.

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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*
DesRosier Thomas
(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)
Director10% Owner
XOfficer (give title below)Other (specify below)
See Remarks
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
08/15/2026		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 Stock08/15/2026M245A(1)8,199D
Common Stock08/17/2026S(2)82D$4.558,117D
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)08/15/2026M133 (3) (3)Common Stock133$0265D
Restricted Stock Units(1)08/15/2026M112 (4) (4)Common Stock112$0667D
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.
Remarks:
EVP and Chief Legal Officer
/s/ Thomas J. DesRosier08/18/2026
** 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