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PureTech (PRTC) details sizable Seaport Therapeutics (SPTX) preferred stake

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
3

Rhea-AI Filing Summary

PureTech Health plc, through its subsidiary PureTech LYT, Inc., has filed an initial ownership report for Seaport Therapeutics, Inc. (SPTX). The filing shows indirect holdings of 302,479 shares of common stock and several series of preferred stock.

PureTech LYT, Inc. is the record holder of all reported securities, while PureTech Health plc ultimately controls voting and disposition through an intermediate LLC. The Series A-1, A-2 and B preferred shares are convertible into common stock at the holder’s election and will automatically convert into common stock upon the closing of Seaport’s initial public offering, for no additional consideration.

Positive

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Insider PureTech Health plc, PureTech LYT, Inc.
Role null | null
Type Security Shares Price Value
holding Series A-1 Preferred Stock -- -- --
holding Series A-2 Preferred Stock -- -- --
holding Series B Preferred Stock -- -- --
holding Common Stock -- -- --
Holdings After Transaction: Series A-1 Preferred Stock — 12,736,014 shares (Indirect, See footnote); Series A-2 Preferred Stock — 2,681,265 shares (Indirect, See footnote); Series B Preferred Stock — 965,255 shares (Indirect, See footnote); Common Stock — 302,479 shares (Indirect, See footnote)
Footnotes (1)
  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. 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.
Common Stock held 302,479 shares Indirect holdings reported on Form 3
Series B Preferred underlying common 965,255 shares Indirect; convertible into common stock
Series A-2 Preferred underlying common 2,681,265 shares Indirect; convertible into common stock
Series A-1 Preferred underlying common 12,736,014 shares Indirect; convertible into common stock
Preferred conversion price $0.0000 per share Series A-1, A-2, B preferred into common
ten percent owner financial
"PureTech Health plc and PureTech LYT, Inc. are each marked as a ten percent owner."
preferred stock financial
"The filing lists Series A-1 Preferred Stock, Series A-2 Preferred Stock 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.
convertible financial
"The shares of Issuer's preferred stock have no expiration date and are convertible at the holder's election into Issuer's common stock."
A convertible is a type of investment that starts as a loan or preferred stake (like a bond or preferred share) but can be exchanged for common shares of the company at a set price or under certain conditions. It matters to investors because it offers a mix of steady income and downside protection like a loan, plus the upside of stock ownership if the company does well—similar to holding a coupon that you can trade for a full ticket if the event becomes valuable.
initial public offering financial
"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."
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.
indirect ownership financial
"All reported securities are held indirectly through PureTech LYT, Inc. with PureTech Health plc controlling voting and disposition."
SEC Form 3
FORM 3UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF 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
OMB APPROVAL
OMB Number:3235-0104
Estimated average burden
hours per response:0.5
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. Date of Event Requiring Statement (Month/Day/Year)
04/30/2026
3. Issuer Name and Ticker or Trading Symbol
Seaport Therapeutics, Inc. [ SPTX ]
3a. Foreign Trading Symbol
5. If Amendment, Date of Original Filed (Month/Day/Year)
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
DirectorX10% Owner
Officer (give title below)Other (specify below)
6. Individual or Joint/Group Filing (Check Applicable Line)
Form filed by One Reporting Person
XForm filed by More than One Reporting Person
Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock302,479ISee footnote(1)
Table II - Derivative Securities Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4) 2. Date Exercisable and Expiration Date (Month/Day/Year)3. Title and Amount of Securities Underlying Derivative Security (Instr. 4) 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 6. Nature of Indirect Beneficial Ownership (Instr. 5)
Date ExercisableExpiration DateTitleAmount or Number of Shares
Series A-1 Preferred Stock (2) (2)Common Stock12,736,014(2)ISee footnote(1)
Series A-2 Preferred Stock (2) (2)Common Stock2,681,265(2)ISee footnote(1)
Series B Preferred Stock (2) (2)Common Stock965,255(2)ISee footnote(1)
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
DirectorX10% 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
DirectorX10% Owner
Officer (give title below)Other (specify below)
Explanation of Responses:
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.
PureTech LYT, Inc., By: /s/ Robert Lyne04/30/2026
PureTech Health LLC, By: /s/ Robert Lyne04/30/2026
PureTech Health plc, By: /s/ Robert Lyne04/30/2026
** 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 5 (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 3: SEC 1473 (03-26)

FAQ

What does PureTech Health plc report in its Seaport Therapeutics (SPTX) Form 3?

PureTech Health plc reports an indirect ownership stake in Seaport Therapeutics through PureTech LYT, Inc. The filing lists common and multiple preferred share classes that can convert into common stock, outlining PureTech’s structured equity position ahead of Seaport’s initial public offering.

How many Seaport Therapeutics common shares are reported by PureTech on Form 3?

The filing reports 302,479 shares of Seaport Therapeutics common stock held indirectly. These shares are recorded in the name of PureTech LYT, Inc., with PureTech Health plc ultimately controlling voting and disposition power through its ownership of intermediary entities.

What preferred stock holdings in Seaport Therapeutics does PureTech disclose?

PureTech discloses indirect holdings of Series A-1, Series A-2 and Series B preferred stock in Seaport Therapeutics. These preferred shares are convertible into common stock at the holder’s election and are structured to automatically convert into common stock when Seaport’s initial public offering closes.

How is ownership of Seaport Therapeutics structured between PureTech entities?

All reported Seaport securities are held of record by PureTech LYT, Inc. PureTech Health LLC is the sole owner of PureTech LYT, Inc., and PureTech Health plc is the sole member of PureTech Health LLC, giving PureTech Health plc power over voting and disposition decisions.

What happens to Seaport’s preferred stock held by PureTech at the IPO closing?

According to the filing, Seaport’s preferred stock held indirectly by PureTech has no expiration and converts into common stock at the holder’s election. It will automatically convert into common stock, for no additional consideration, upon the closing of Seaport’s initial public offering.