PureTech converts Seaport preferred into common stock

Seaport Therapeutics, Inc. insider entities affiliated with PureTech converted multiple series of preferred stock into Common Stock in connection with the company’s initial public offering.

Rhea-AI Filing Summary

Seaport Therapeutics, Inc. insider entities affiliated with PureTech converted multiple series of preferred stock into Common Stock in connection with the company’s initial public offering. The Form 4 shows automatic conversions of Series A-1, Series A-2 and Series B Preferred Stock into Common Stock on a stated one-for-3.1407 basis.

PureTech LYT, Inc. is the record holder of all reported securities, with PureTech Health LLC and PureTech Health plc controlling voting and disposition power through their ownership chain. The transactions are coded as conversions of derivative securities, increasing indirect Common Stock holdings rather than reflecting open-market buying or selling.

Insider Trade Summary

51,452,630 shares exercised/converted

Exercise 6 txns

Insider PureTech Health plc, PureTech LYT, Inc.

Role 10% Owner | 10% Owner

Type	Security	Shares	Price	Value
Conversion	Series A-1 Preferred Stock	40,000,000	$0.00	$0.00
Conversion	Series A-2 Preferred Stock	8,421,052	$0.00	$0.00
Conversion	Series B Preferred Stock	3,031,578	$0.00	$0.00
Conversion	Common Stock	12,736,014	$0.00	$0.00
Conversion	Common Stock	2,681,265	$0.00	$0.00
Conversion	Common Stock	965,255	$0.00	$0.00

Holdings After Transaction: Series A-1 Preferred Stock — 0 contracts (Indirect, See footnote); Series A-2 Preferred Stock — 0 contracts (Indirect, See footnote); Series B Preferred Stock — 0 contracts (Indirect, See footnote); Common Stock — 16,685,013 shares (Indirect, See footnote)

Footnotes (2)

1. F1. 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. F2. 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.

Key Figures

Series A-1 Preferred converted: 40,000,000 shares Series A-2 Preferred converted: 8,421,052 shares Series B Preferred converted: 3,031,578 shares +4 more

7 metrics

Series A-1 Preferred converted 40,000,000 shares Derivative shares converted into Seaport Therapeutics Common Stock

Series A-2 Preferred converted 8,421,052 shares Derivative shares converted into Seaport Therapeutics Common Stock

Series B Preferred converted 3,031,578 shares Derivative shares converted into Seaport Therapeutics Common Stock

Common from Series A-1 12,736,014 shares Underlying Common Stock received upon A-1 conversion

Common from Series A-2 2,681,265 shares Underlying Common Stock received upon A-2 conversion

Common from Series B 965,255 shares Underlying Common Stock received upon B conversion

Total derivative shares converted 51,452,630 shares Aggregate exerciseShares across all preferred series

Key Terms

Conversion of derivative security, Preferred Stock, initial public offering, ten percent owner, +1 more

5 terms

Conversion of derivative security financial

"transaction_code_description: Conversion of derivative security"

Preferred Stock financial

"Each share of Series A-1, Series A-2 and Series B Preferred Stock"

Preferred stock is a type of ownership in a company that typically offers investors higher and more consistent dividend payments than common stock. Unlike regular shares, preferred stock usually doesn’t come with voting rights but provides a priority claim on the company’s assets and profits, making it a more stable and predictable investment option. This makes preferred stock attractive to those seeking steady income with lower risk.

initial public offering financial

"automatically converted upon the closing of the Issuer's initial public offering"

An initial public offering (IPO) is when a private company first sells its shares to the public and becomes a stock-listed company. It matters because it allows the company to raise money from a wide range of investors, helping it grow, while giving early shareholders a way to sell some of their ownership.

ten percent owner financial

"is_ten_percent_owner: 1 for each reporting person"

indirect ownership financial

"ownership_type: indirect and nature_of_ownership: See footnote"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did PureTech report in Seaport Therapeutics (SPTX) Form 4?

The Form 4 reports automatic conversions of multiple Seaport Therapeutics preferred stock series into Common Stock. These are classified as derivative security conversions, not open-market purchases or sales, and occur in connection with the company’s initial public offering.

Which Seaport Therapeutics preferred shares were converted by PureTech-related entities?

Series A-1, Series A-2 and Series B Preferred Stock were converted into Seaport Therapeutics Common Stock. Each series converted on a one-for-3.1407 basis, as disclosed, with no additional consideration paid and no expiration date on the preferred shares before conversion.

How many Seaport Therapeutics Common Shares did the preferred stock conversions generate?

The filing shows conversions into 12,736,014; 2,681,265; and 965,255 Seaport Therapeutics Common Shares from the A-1, A-2 and B Preferred series, respectively. These amounts are reported as indirect holdings controlled through PureTech’s ownership structure.

Who is the record holder of the Seaport Therapeutics shares in this Form 4?

PureTech LYT, Inc. is the record holder of all reported Seaport Therapeutics securities. PureTech Health LLC owns PureTech LYT, Inc., and PureTech Health plc is the sole member of PureTech Health LLC, directing voting and disposition of these securities.

Does this Seaport Therapeutics Form 4 show any open-market buying or selling?

No open-market buying or selling is reported. All transactions use code C, described as conversion of derivative securities, reflecting preferred stock automatically converting into Common Stock tied to Seaport Therapeutics’ initial public offering terms.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/06/2026 - 07:38 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED 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

X

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 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^*

PureTech Health plc

(Last) (First) (Middle)

6 TIDE STREET, SUITE 400

(Street)

BOSTON MASSACHUSETTS 02210

(City) (State) (Zip)

UNITED STATES

(Country)

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)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/04/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	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)
			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)

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)
				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)

1. Name and Address of Reporting Person^*

PureTech Health plc

(Last) (First) (Middle)

6 TIDE STREET, SUITE 400

(Street)

BOSTON MASSACHUSETTS 02210

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

PureTech LYT, Inc.

(Last) (First) (Middle)

6 TIDE STREET, SUITE 400

(Street)

BOSTON MASSACHUSETTS 02210

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

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.

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