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

Officer at Seres Therapeutics (NASDAQ: MCRB) sells 79 shares under 10b5-1 tax plan

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

Rhea-AI Filing Summary

Seres Therapeutics, Inc. officer Thomas DesRosier reported a small set of equity transactions. He sold 79 shares of common stock at $7.53 per share in an open-market sale executed under a pre-arranged Rule 10b5-1 plan intended to cover taxes from restricted stock unit (RSU) vesting.

On the same date, RSUs covering 244 shares were converted into common stock at a $0.00 exercise price, and additional RSUs for 111 and 133 shares converted into common stock. After these transactions, he directly holds 7,954 common shares plus remaining RSU awards that continue to vest over time.

Positive

  • None.

Negative

  • None.
Insider DesRosier Thomas
Role See Remarks
Sold 79 shs ($594.87)
Type Security Shares Price Value
Sale Common Stock 79 $7.53 $594.87
Exercise Restricted Stock Units 133 $0.00 --
Exercise Restricted Stock Units 111 $0.00 --
Exercise Common Stock 244 $0.00 --
Holdings After Transaction: Common Stock — 7,954 shares (Direct, null); Restricted Stock Units — 398 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.
Shares sold 79 shares Open-market sale at $7.53 per share
Sale price $7.53/share Price for 79 common shares sold
Shares after transactions 7,954 shares Common stock directly held post-transaction
RSU conversion 1 244 shares Common shares from derivative exercise at $0.00
RSU conversion 2 111 shares Restricted Stock Units converted into common stock
RSU conversion 3 133 shares Restricted Stock Units converted into common stock
Net buy/sell direction net-sell of 79 shares Aggregate of buy/sell activity in this filing
Exercise transactions 2 exercises, 244 shares Derivative exercises reported in transaction summary
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.
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.
open-market sale financial
"transaction_action": "open-market sale""
An open-market sale is when a shareholder sells existing shares directly on a public exchange to any willing buyer, rather than through a private deal. Think of it like putting goods on a busy market stall where price is set by supply and demand; for investors it matters because such sales increase available supply, can put short-term downward pressure on the stock price, and signal changes in liquidity or investor confidence.
derivative security financial
"transaction_code_description": "Exercise or conversion of derivative security""
A derivative security is a financial contract whose value comes from the price or performance of something else, such as a stock, bond, commodity, or market index. For investors it acts like an insurance policy or a wager: it can be used to protect against losses, lock in prices, or amplify gains and losses, so it can change a portfolio’s risk and potential return without owning the underlying asset directly.
vesting financial
"restricted stock units vested and settled as to 25% on February 15, 2024"
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.
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)
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 Stock05/15/2026M244A(1)8,033D
Common Stock05/18/2026S(2)79D$7.537,954D
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)05/15/2026M133 (3) (3)Common Stock133$0398D
Restricted Stock Units(1)05/15/2026M111 (4) (4)Common Stock111$0779D
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. DesRosier05/19/2026
** 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 MCRB officer Thomas DesRosier report?

Thomas DesRosier reported selling 79 Seres Therapeutics shares and exercising RSU-related awards for 244, 111, and 133 shares. These actions reflect routine equity compensation activity rather than a large discretionary trade.

At what price were Seres Therapeutics (MCRB) shares sold in this Form 4?

The reported sale occurred at an average price of $7.53 per share for 79 Seres Therapeutics common shares. This was an open-market transaction disclosed as part of a broader set of equity compensation-related moves.

How many Seres Therapeutics shares does Thomas DesRosier hold after the Form 4 transactions?

Following these transactions, Thomas DesRosier holds 7,954 Seres Therapeutics common shares directly. He also retains unvested restricted stock units, which represent additional potential shares that vest and settle over a set quarterly schedule.

Were the Seres Therapeutics insider sales made under 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, intended solely to cover taxes arising from the vesting of restricted stock units granted to the officer.

What do the restricted stock unit (RSU) transactions mean for MCRB’s insider ownership?

Each RSU represents a right to receive one Seres Therapeutics share. The filing notes vesting schedules that started on February 15, 2024 and February 15, 2025, with the remaining RSUs vesting in equal quarterly installments and having no expiration date.

Is the Seres Therapeutics Form 4 sale by Thomas DesRosier a large position change?

The sale involved 79 shares compared with 7,954 shares held afterward, indicating a modest reduction. Footnotes explain the sale’s purpose was tax coverage for RSU vesting, suggesting it is routine compensation-related activity rather than a major strategic sale.