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ARCH Venture Fund XII and affiliated entities filed a Schedule 13D reporting beneficial ownership of 6,294,951 shares of Seaport Therapeutics, Inc. common stock, representing 11.9% of the outstanding shares. The position was built through preferred stock investments in 2024 that converted into common stock at the IPO, plus a purchase of 1,100,000 common shares at $18.00 per share on May 1, 2026. In total, AVF XII invested about $89,799,993.80 to acquire these securities. The shares are held for investment purposes, and the fund has registration rights and is subject to a 180-day lock-up period after April 30, 2026, limiting near-term sales without underwriter and issuer consent.
Zohar Daphne reported acquisition or exercise transactions in this Form 4 filing.
Seaport Therapeutics, Inc. reported that Chief Executive Officer Daphne Zohar received two stock option grants on April 30, 2026 for 1,486,786 and 271,813 options to buy common stock at $18.00 per share, expiring on April 29, 2036. The options vest in forty-eight equal monthly installments after April 30, 2026, conditioned on her continued service.
Seaport Therapeutics, Inc. reported that investment fund Sofinnova Venture Partners XI, L.P. converted its preferred stock into common shares in connection with the closing of the company’s initial public offering. The transactions are attributed to Sofinnova, not directly to director James Healy, who is a managing member of the fund’s general partner and disclaims beneficial ownership except for any pecuniary interest.
Sofinnova converted 2,526,315 shares of Series B Preferred Stock into 804,379 shares of common stock and 6,052,631 shares of Series A-2 Preferred Stock into 1,927,159 shares of common stock, based on a one-for-3.1407 conversion ratio. Following these conversions, Sofinnova directly holds 2,731,538 common shares of Seaport Therapeutics.
Seaport Therapeutics, Inc. director David E. Wheadon received a grant of stock options covering 12,258 shares of common stock. The options have an exercise price of $18.00 per share and expire on April 29, 2036. All 12,258 underlying shares vest in full on April 30, 2027, subject to his continued service, and this grant represents his entire reported option position in this filing.
Seaport Therapeutics director Sandra E. Peterson received a grant of stock options representing 12,258 shares of common stock. The options have an exercise price of $18.00 per share and expire on April 29, 2036. According to the footnote, all 12,258 underlying shares vest in full on April 30, 2027, subject to her continued service with the company.
Seaport Therapeutics Chief Scientific Officer Michael Cunyuan Chen reported equity-related acquisitions. On May 4, 2026, he acquired 3,351 shares of Common Stock through the conversion of 10,526 shares of Series B Preferred Stock, which automatically converted in connection with the company’s initial public offering on a one-for-3.1407 basis.
After this conversion, he directly held 3,351 common shares. Separately, on April 30, 2026, he received a grant of stock options for 63,680 shares of Common Stock at an exercise price of $18.00 per share, expiring on April 29, 2036. These options vest in 48 equal monthly installments following April 30, 2026, subject to his continued service.
Seaport Therapeutics director Denice Torres reported equity-related changes tied to the company’s initial public offering and board compensation. A revocable trust associated with her converted 42,105 shares of Series B Preferred Stock into 13,406 shares of Common Stock on a one-for-one basis upon the IPO closing on May 4, 2026, with no additional consideration.
Separately, she received a stock option grant for 12,258 shares of Common Stock at an exercise price of $18.00 per share. This option expires on April 29, 2036 and will vest in full on April 30, 2027, subject to her continued service.
ARCH Venture Fund XII, L.P., a 10% owner of Seaport Therapeutics, Inc., increased its indirect position through an open-market purchase and preferred stock conversions. On May 4, 2026, ARCH XII bought 1,100,000 shares of common stock at $18.00 per share in an open-market transaction.
On the same date, ARCH XII also converted 2,681,265 shares of Series B Preferred Stock and 2,513,686 shares of Series A-2 Preferred Stock into common stock, eliminating these preferred positions. Following these transactions, ARCH XII indirectly held 6,294,951 shares of Seaport Therapeutics common stock through its fund structure.
Seaport Therapeutics Chief Medical Officer Antony Loebel reported equity-related changes in his holdings. He converted 63,157 shares of Series B Preferred Stock into 20,109 shares of Common Stock on a one‑for‑3.1407 basis, tied to the closing of the company’s initial public offering, and now holds 20,109 common shares directly.
On a separate date, he received a stock option for 63,680 shares of Common Stock at an exercise price of $18.00 per share, expiring on April 29, 2036. These option shares vest in 48 equal monthly installments following April 30, 2026, contingent on his continued service, and represent compensation rather than open‑market trading.