Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * PureTech Health plc 2. Issuer Name and Ticker or Trading Symbol Seaport Therapeutics, Inc. [SPTX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 6 TIDE STREET, SUITE 400 3. Date of Earliest Transaction (Month/Day/Year) 05/04/2026 (Street) BOSTON, MA 02210 4. If Amendment, Date Original Filed (Month/Day/Year) 6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) 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 05/04/2026 C 12,736,014 A (1) 13,038,493 I See footnote(2) Common Stock 05/04/2026 C 2,681,265 A (1) 15,719,758 I See footnote(2) Common Stock 05/04/2026 C 965,255 A (1) 16,685,013 I See footnote(2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 Underlying Securities (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 of Derivative Security: 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

Series A-1 Preferred Stock

(1)

05/04/2026

C

40,000,000

(1)

(1)

Common Stock

12,736,014

$ 0

0

I

See footnote(2)

Series A-2 Preferred Stock

(1)

05/04/2026

C

8,421,052

(1)

(1)

Common Stock

2,681,265

$ 0

0

I

See footnote(2)

Series B Preferred Stock

(1)

05/04/2026

C

3,031,578

(1)

(1)

Common Stock

965,255

$ 0

0

I

See footnote(2)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
PureTech Health plc 6 TIDE STREET, SUITE 400 BOSTON, MA 02210		X
PureTech LYT, Inc. 6 TIDE STREET, SUITE 400 BOSTON, MA 02210		X

Signatures

PureTech LYT, Inc., By: /s/ Robert Lyne		05/06/2026
**Signature of Reporting Person		Date
PureTech Health LLC, By: /s/ Robert Lyne		05/06/2026
**Signature of Reporting Person		Date
PureTech Health plc, By: /s/ Robert Lyne		05/06/2026
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Each share of Series A-1, Series A-2 and Series B Preferred Stock (collectively, the "Preferred Stock") was convertible into Common Stock of the Issuer on a one-for-3.1407 basis at the option of the holder, and automatically converted upon the closing of the Issuer's initial public offering without payment of further consideration. The Preferred Stock had no expiration date.
(2)	PureTech LYT, Inc. is the record holder of all of the securities reported in this Form 4. PureTech Health LLC is the sole owner of PureTech LYT, Inc. PureTech Health plc is the sole member of PureTech Health LLC, and has the power to direct the voting and disposition of securities held by PureTech LYT, Inc. and PureTech Health LLC.

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