Seaport Therapeutics, Inc.

Item 2. Unregistered Sales of Equity Securities and Use of Proceeds.

(a) Recent Sales of Unregistered Equity Securities

Set forth below is information regarding securities we have issued within the past three years that were not registered under the Securities Act.

Preferred Stock Issuances

In April 2024, we issued an aggregate of 40,000,000 shares of Series A-1 convertible preferred stock in connection with entry into an asset transfer agreement, dated as of April 8, 2024, or the Asset Transfer Agreement, with PureTech LYT. We also issued and sold to accredited investors an aggregate of 26,342,102 shares of Series A-2 convertible preferred stock at a price per share of $3.80, for an aggregate purchase price of $100.1 million. In October and November 2024, we issued and sold to accredited investors an aggregate of 47,578,934 shares of Series B convertible preferred stock at a price per share of $4.75, for an aggregate purchase price of approximately $226.0 million.

Common Stock Issuances

In April 2024, we issued an aggregate of 318 shares of common stock to PureTech LYT in connection with our formation. In April 2024, we issued an aggregate of 302,161 shares of common stock to PureTech LYT in connection with the Asset Transfer Agreement.

Since April 2024, we have sold or issued by exchange to our founders an aggregate of 2,292,481 shares of restricted common stock under our 2024 Plan or pursuant to agreement, at a purchase price of $0.0 million.

Grants and exercises of stock options

Since April 2024, we have granted certain employees, consultants, and directors options to purchase an aggregate of 9,916,296 shares of our common stock under our 2024 Plan and 2026 Plan, at exercise prices ranging from $3.05 to $10.31 per share.

Since April 2024, 216,457 stock options have been exercised under our 2024 Plan and 2026 Plan at a weighted average purchase price of $3.73 per share.

None of the foregoing transactions involved any underwriters, underwriting discounts or commissions, or any public offering. Unless otherwise specified above, the Registrant believes these transactions were exempt from registration under the Securities Act in reliance on Section 4(a)(2) of the Securities Act (and Regulation D or Regulation S promulgated thereunder) or Rule 701 promulgated under Section 3(b) of the Securities Act as transactions by an issuer not involving any public offering or under benefit plans and contracts relating to compensation as provided under Rule 701. The recipients of the securities in each of these transactions represented their intentions to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were placed on the share certificates issued in these transactions. All recipients had adequate access, through their relationships with the Registrant, to information about the Registrant. The sales of these securities were made without any general solicitation or advertising.

(b) Use of Proceeds from our Initial Public Offering

On May 1, 2026, the SEC declared effective our registration statement on Form S-1 (File No. 333-294976), as amended, or the Registration Statement, filed in connection with our IPO. Pursuant to the Registration Statement, we registered the offer and sale of 14,160,000 shares of our common stock with a maximum aggregate offering price of approximately $237.0 million. Goldman Sachs & Co. LLC, J.P. Morgan, Leerink Partners, Citigroup, and Stifel acted as representatives of the underwriters for the IPO. None of the expenses associated with the IPO were paid to directors, officers, persons owning 10% or more of any class of equity securities, or to our affiliates.

There has been no material change in the expected use of the net proceeds from our IPO as described in our final prospectus filed with the SEC pursuant to Rule 424(b) of the Securities Act on May 1, 2026.

(c) Issuer Repurchases of Securities

None.