# EDGAR Filing Document

**Accession Number:** 0001782999
**File Stem:** 0001193125-26-198652
**Filing Date:** 2026-4
**Character Count:** 7215
**Document Hash:** 83b40012cffebeaa20dd003a5f2623e5
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-198652.hdr.sgml**: 20260430

**ACCESSION NUMBER**: 0001193125-26-198652

**CONFORMED SUBMISSION TYPE**: 3

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20260430

**FILED AS OF DATE**: 20260430

**DATE AS OF CHANGE**: 20260430

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** PureTech Health plc
- **CENTRAL INDEX KEY:** 0001782999
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **STATE OF INCORPORATION:** X0
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 3
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-43254
- **FILM NUMBER:** 26928504

**BUSINESS ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02210
- **BUSINESS PHONE:** 617-482-2333

**MAIL ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02210
**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** PureTech LYT, Inc.
- **CENTRAL INDEX KEY:** 0002131815

**ORGANIZATION NAME:**
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 3
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-43254
- **FILM NUMBER:** 26928503

**BUSINESS ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02210
- **BUSINESS PHONE:** (617) 482-2333

**MAIL ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02210
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Seaport Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0002042347
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 992235719
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02110
- **BUSINESS PHONE:** 617-807-4062

**MAIL ADDRESS:**
- **STREET 1:** 6 TIDE STREET
- **STREET 2:** SUITE 400
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02110

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 3

### INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>PureTech Health plc<br><sub>(Last) (First) (Middle)</sub><br>6 TIDE STREET, SUITE 400<br><sub>(Street)</sub><br>BOSTON, MA 02210<br><sub>(City) (State) (Zip)</sub> | **3. Issuer Name and Ticker or Trading Symbol**<br>Seaport Therapeutics, Inc. [ SPTX ] | **5. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  |
| **2. Date of Event Requiring Statement (Month/Day/Year)**<br>2026-04-30 | **4. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[ ] Director   [X] 10% Owner<br>[ ] Officer (give title below)   [ ] Other (specify below)<br>_ _ | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[ ] Form filed by One Reporting Person<br>[X] Form filed by More than One Reporting Person |

---

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>PureTech LYT, Inc.<br><sub>(Last) (First) (Middle)</sub><br>6 TIDE STREET, SUITE 400<br><sub>(Street)</sub><br>BOSTON, MA 02210<br><sub>(City) (State) (Zip)</sub> | **3. Issuer Name and Ticker or Trading Symbol**<br>Seaport Therapeutics, Inc. [ SPTX ] | **5. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  |
| **2. Date of Event Requiring Statement (Month/Day/Year)**<br>2026-04-30 | **4. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[ ] Director   [X] 10% Owner<br>[ ] Officer (give title below)   [ ] Other (specify below)<br>_ _ | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[ ] Form filed by One Reporting Person<br>[X] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities Beneficially Owned

---

|  |  |  |  |
| --- | --- | --- | --- |
| 1. Title of Security | 2. Amount of Securities Beneficially Owned | 3. Ownership Form | 4. Nature of Indirect Beneficial Ownership |
| Common Stock | 302479 | I | See footnote<sup>(1)</sup> |

---

## Table II - Derivative Securities Beneficially Owned

---

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 3. Title and Amount of Underlying Securities | 3. Title and Amount of Underlying Securities | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| Series A-1 Preferred Stock | <sup>(2)</sup> | <sup>(2)</sup> | Common Stock | 12736014 | <sup>(2)</sup> | I | See footnote<sup>(1)</sup> |
| Series A-2 Preferred Stock | <sup>(2)</sup> | <sup>(2)</sup> | Common Stock | 2681265 | <sup>(2)</sup> | I | See footnote<sup>(1)</sup> |
| Series B Preferred Stock | <sup>(2)</sup> | <sup>(2)</sup> | Common Stock | 965255 | <sup>(2)</sup> | I | See footnote<sup>(1)</sup> |

---

### Footnotes:

(1) PureTech LYT, Inc. is the record holder of all of the securities reported in this Form 3. 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.

(2) The shares of Issuer's preferred stock have no expiration date and are convertible at the holder's election into Issuer's common stock. The preferred stock will automatically convert into shares of the Issuer's common stock, for no additional consideration, upon the closing of the Issuer's initial public offering.

**Signature:** PureTech LYT, Inc., By:  /s/ Robert Lyne  
**Date:** 2026-04-30

**Signature:** PureTech Health LLC, By:  /s/ Robert Lyne  
**Date:** 2026-04-30

**Signature:** PureTech Health plc, By:  /s/ Robert Lyne  
**Date:** 2026-04-30

### Remarks:

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.**