SPTX · Seaport Therapeutics, Inc.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $17.65 to $18.27, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range.

The Reporting Person disclaims beneficial ownership of such shares for purposes of Section 16 of the Exchange Act, except to the extent of his pecuniary interest therein, if any. This report shall not be deemed an admission that he is a beneficial owner of such shares for the purpose of Section 16 of the Exchange Act, or for any other purpose.

Each share of Series B Preferred Stock (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.

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.

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.

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.

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.

Each share of Series B Preferred Stock (the "Preferred Stock") was convertible into Common Stock of the Issuer on a one-for-one basis at the option of the holder, and automatically converted upon the closing of the Issuer's initial public offering on May 4, 2026 without payment of further consideration. The Preferred Stock had no expiration date.

The Reporting Person disclaims beneficial ownership of such shares for purposes of Section 16 of the Exchange Act, except to the extent of her pecuniary interest therein, if any. This report shall not be deemed an admission that she is a beneficial owner of such shares for the purpose of Section 16 of the Exchange Act, or for any other purpose.

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.

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.

Each share of Series B Preferred Stock (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.

Each share of Series B Preferred Stock (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.

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.

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.

Each share of Series B Preferred Stock (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.

Each share of 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.

Shares held directly by ARCH Venture Fund XII, L.P. ("ARCH XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP") is the sole general partner of ARCH XII. ARCH Venture Partners XII, LLC ("AVP XII LLC") is the sole general partner of AVP XII LP. Keith Crandell, Kristina Burow, Steven Gillis and Robert Nelsen are members of the investment committee of AVP XII LLC (the "AVP XII LLC Committee Members"). Each of AVP XII LP and AVP XII LLC may be deemed to beneficially own the shares held by ARCH XII, and each of the AVP XII LLC Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH XII. Each of AVP XII LP, AVP XII LLC and the AVP XII LLC Committee Members disclaims beneficial ownership except to the extent of their pecuniary interest therein, if any.

Each share of 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.

These shares are directly held by Sofinnova Venture Partners XI, L.P. ("SVP XI"). Sofinnova Management XI, L.P. ("SM XI LP") is the general partner of SVP XI, and Sofinnova Management XI, L.L.C. ("SM XI") is the general partner of SM XI LP. The Reporting Person is a managing member of SM XI and may be deemed to share voting and investment discretion with respect to securities directly held by SVP XI. The Reporting Person disclaims beneficial ownership of the securities directly held by SVP XI. This report shall not be construed as an admission that he is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose, except to the extent of his pecuniary interest therein, if any.

Each share of 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.

These shares are directly held by Sofinnova Venture Partners XI, L.P. ("SVP XI"). Sofinnova Management XI, L.P. ("SM XI LP") is the general partner of SVP XI, and Sofinnova Management XI, L.L.C. ("SM XI") is the general partner of SM XI LP. The Reporting Person is a managing member of SM XI and may be deemed to share voting and investment discretion with respect to securities directly held by SVP XI. The Reporting Person disclaims beneficial ownership of the securities directly held by SVP XI. This report shall not be construed as an admission that he is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose, except to the extent of his pecuniary interest therein, if any.

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.

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.

Each share of Series B Preferred Stock (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.

The Reporting Person disclaims beneficial ownership of such shares for purposes of Section 16 of the Exchange Act, except to the extent of her pecuniary interest therein, if any. This report shall not be deemed an admission that she is a beneficial owner of such shares for the purpose of Section 16 of the Exchange Act, or for any other purpose.

Each share of 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.

These shares are directly held by Sofinnova Venture Partners XI, L.P. ("SVP XI"). Sofinnova Management XI, L.P. ("SM XI LP") is the general partner of SVP XI, and Sofinnova Management XI, L.L.C. ("SM XI") is the general partner of SM XI LP. The Reporting Person is a managing member of SM XI and may be deemed to share voting and investment discretion with respect to securities directly held by SVP XI. The Reporting Person disclaims beneficial ownership of the securities directly held by SVP XI. This report shall not be construed as an admission that he is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose, except to the extent of his pecuniary interest therein, if any.

Each share of 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.

These shares are directly held by Sofinnova Venture Partners XI, L.P. ("SVP XI"). Sofinnova Management XI, L.P. ("SM XI LP") is the general partner of SVP XI, and Sofinnova Management XI, L.L.C. ("SM XI") is the general partner of SM XI LP. The Reporting Person is a managing member of SM XI and may be deemed to share voting and investment discretion with respect to securities directly held by SVP XI. The Reporting Person disclaims beneficial ownership of the securities directly held by SVP XI. This report shall not be construed as an admission that he is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose, except to the extent of his pecuniary interest therein, if any.

Each share of 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.

Shares held directly by ARCH Venture Fund XII, L.P. ("ARCH XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP") is the sole general partner of ARCH XII. ARCH Venture Partners XII, LLC ("AVP XII LLC") is the sole general partner of AVP XII LP. Keith Crandell, Kristina Burow, Steven Gillis and Robert Nelsen are members of the investment committee of AVP XII LLC (the "AVP XII LLC Committee Members"). Each of AVP XII LP and AVP XII LLC may be deemed to beneficially own the shares held by ARCH XII, and each of the AVP XII LLC Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH XII. Each of AVP XII LP, AVP XII LLC and the AVP XII LLC Committee Members disclaims beneficial ownership except to the extent of their pecuniary interest therein, if any.

Each share of Series B Preferred Stock (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.

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.

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.

Each share of Series B Preferred Stock (the "Preferred Stock") was convertible into Common Stock of the Issuer on a one-for-one basis at the option of the holder, and automatically converted upon the closing of the Issuer's initial public offering on May 4, 2026 without payment of further consideration. The Preferred Stock had no expiration date.

The Reporting Person disclaims beneficial ownership of such shares for purposes of Section 16 of the Exchange Act, except to the extent of her pecuniary interest therein, if any. This report shall not be deemed an admission that she is a beneficial owner of such shares for the purpose of Section 16 of the Exchange Act, or for any other purpose.

Each share of 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.

Shares held directly by ARCH Venture Fund XII, L.P. ("ARCH XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP") is the sole general partner of ARCH XII. ARCH Venture Partners XII, LLC ("AVP XII LLC") is the sole general partner of AVP XII LP. Keith Crandell, Kristina Burow, Steven Gillis and Robert Nelsen are members of the investment committee of AVP XII LLC (the "AVP XII LLC Committee Members"). Each of AVP XII LP and AVP XII LLC may be deemed to beneficially own the shares held by ARCH XII, and each of the AVP XII LLC Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH XII. Each of AVP XII LP, AVP XII LLC and the AVP XII LLC Committee Members disclaims beneficial ownership except to the extent of their pecuniary interest therein, if any.

Shares held directly by ARCH Venture Fund XII, L.P. ("ARCH XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP") is the sole general partner of ARCH XII. ARCH Venture Partners XII, LLC ("AVP XII LLC") is the sole general partner of AVP XII LP. Keith Crandell, Kristina Burow, Steven Gillis and Robert Nelsen are members of the investment committee of AVP XII LLC (the "AVP XII LLC Committee Members"). Each of AVP XII LP and AVP XII LLC may be deemed to beneficially own the shares held by ARCH XII, and each of the AVP XII LLC Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH XII. Each of AVP XII LP, AVP XII LLC and the AVP XII LLC Committee Members disclaims beneficial ownership except to the extent of their pecuniary interest therein, if any.

Each share of Series B Preferred Stock (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.

The Reporting Person disclaims beneficial ownership of such shares for purposes of Section 16 of the Exchange Act, except to the extent of her pecuniary interest therein, if any. This report shall not be deemed an admission that she is a beneficial owner of such shares for the purpose of Section 16 of the Exchange Act, or for any other purpose.

Each share of 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.

Shares held directly by ARCH Venture Fund XII, L.P. ("ARCH XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP") is the sole general partner of ARCH XII. ARCH Venture Partners XII, LLC ("AVP XII LLC") is the sole general partner of AVP XII LP. Keith Crandell, Kristina Burow, Steven Gillis and Robert Nelsen are members of the investment committee of AVP XII LLC (the "AVP XII LLC Committee Members"). Each of AVP XII LP and AVP XII LLC may be deemed to beneficially own the shares held by ARCH XII, and each of the AVP XII LLC Committee Members may be deemed to share the power to direct the disposition and vote of the shares held by ARCH XII. Each of AVP XII LP, AVP XII LLC and the AVP XII LLC Committee Members disclaims beneficial ownership except to the extent of their pecuniary interest therein, if any.

Each share of Series B Preferred Stock (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.

Each share of Series B Preferred Stock (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.

Each share of Series B Preferred Stock (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.

1/3rd of the shares underlying this option shall vest and become exercisable on April 30, 2027, with the remaining shares vesting in twenty-four (24) equal monthly installments thereafter, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in full on April 30, 2027, subject to the Reporting Person's continued service on such vesting date.

The shares underlying this option shall vest in full on April 30, 2027, subject to the Reporting Person's continued service on such vesting date.

The shares underlying this option shall vest in full on April 30, 2027, subject to the Reporting Person's continued service on such vesting date.

The shares underlying this option shall vest in forty-eight (48) equal monthly installments following April 30, 2026, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in forty-eight (48) equal monthly installments following April 30, 2026, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in full on April 30, 2027, subject to the Reporting Person's continued service on such vesting date.

The shares underlying this option shall vest in forty-eight (48) equal monthly installments following April 30, 2026, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in forty-eight (48) equal monthly installments following April 30, 2026, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in forty-eight (48) equal monthly installments following April 30, 2026, subject to the Reporting Person's continued service on each such vesting date.

The shares underlying this option shall vest in full on April 30, 2027, subject to the Reporting Person's continued service on such vesting date.