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SCHEDULE 13D/A 0001193125-24-167893 0001117003 XXXXXXXX LIVE 1 Common Stock, $0.0001 par value per share. 02/05/2025 false 0001681087 878972108 Tectonic Therapeutic, Inc. 490 Arsenal Way Suite 210 Watertown MA 02472 Lauren Crockett (781) 290-0770 One Marina Park Drive 8th Floor Boston MA 02210 0001117003 N Terrance McGuire b AF N X1 0 1157977 0 1157977 1157977 N 6.3 IN Consists of (i) 20,262 shares of Common Stock (as defined in Item 1 of the Original Schedule 13D (as defined below)) held by PFC I (as defined in Item 2(a) of the Original Schedule 13D), (ii) 64,652 shares of Common Stock held by PFC II (as defined in Item 2(a) of the Original Schedule 13D) and (iii) 1,073,063 shares of Common Stock held by PP IX (as defined in Item 2(a) of the Original Schedule 13D). The aggregate amount beneficially owned does not include 11,760 shares of Common Stock granted to Mr. McGuire in his capacity as a director of the Issuer because such shares are not exercisable as of the date of filing this Amendment (as defined in Item 1 below) or within 60 days thereafter. PFCM I (as defined in Item 2(a) of the Original Schedule 13D) is the general partner of PFC I. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's (as defined in Item 1 of the Original Schedule 13D) board of directors, are managing members of PFCM I. Each of PFCM I, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC I. PFCM II (as defined in Item 2(a) of the Original Schedule 13D) is the general partner of PFC II. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM II. Each of PFCM II, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC II. PP GP IX (as defined in Item 2(a) of the Original Schedule 13D) is the general partner of PP IX. The PP GP IX Managing Members (as defined in Item 2(c) of the Original Schedule 13D) are the managing members of PP GP IX, and Mr. McGuire, a member of the Issuer's board of directors, is an interest holder in PP GP IX. Each of PP GP IX, the PP GP IX Managing Members and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PP IX. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarter-ended September 30, 2024, filed with the Securities and Exchange Commission (the "Commission") on November 12, 2024 (the "Form 10-Q") plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in a private placement (the "Private Placement"), as reported by the Issuer in its Current Report on Form 8-K, filed with the Commission on February 3, 2025 (the "Form 8-K"). 0001779755 N Polaris Partners IX, L.P. b WC N DE 0 1073063 0 1073063 1073063 N 5.8 PN All shares are held of record by PP IX. PP GP IX is the general partner of PP IX. The PP GP IX Managing Members are the managing members of PP GP IX, and Mr. McGuire, a member of the Issuer's board of directors, is an interest holder in PP GP IX. Each of PP GP IX, the PP GP IX Managing Members and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PP IX. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. 0001877150 N Polaris Partners GP IX, L.L.C. b AF N DE 0 1073063 0 1073063 1073063 N 5.8 OO All shares are held of record by PP IX. PP GP IX is the general partner of PP IX. The PP GP IX Managing Members are the managing members of PP GP IX, and Mr. McGuire, a member of the Issuer's board of directors, is an interest holder in PP GP IX. Each of PP GP IX, the PP GP IX Managing Members and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PP IX. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. Y Polaris Founders Capital Fund I, L.P. b WC N DE 0 20262 0 20262 20262 N 0.1 PN All shares are held of record by PFC I. PFCM I is the general partner of PFC I. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM I. Each of PFCM I, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC I. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. Y Polaris Founders Capital Fund Management Co. I, L.L.C. b AF N DE 0 20262 0 20262 20262 N 0.1 OO All shares are held of record by PFC I. PFCM I is the general partner of PFC I. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM I. Each of PFCM I, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC I. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. Y Polaris Founders Capital Fund II, L.P. b WC N DE 0 64652 0 64652 64652 N 0.4 PN All shares are held of record by PFC II. PFCM II is the general partner of PFC II. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM II. Each of PFCM II, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC II. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. Y Polaris Founders Capital Fund Management Co. II, L.L.C. b AF N DE 0 64652 0 64652 64652 N 0.4 OO All shares are held of record by PFC II. PFCM II is the general partner of PFC II. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM II. Each of PFCM II, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC II. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. 0001295676 N Jonathan Flint b AF N X1 0 84914 0 84914 84914 N 0.5 IN Consists of (i) 20,262 shares of Common Stock held by PFC I and (ii) 64,652 shares of Common Stock held by PFC II. PFCM I is the general partner of PFC I. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM I. Each of PFCM I, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC I. PFCM II is the general partner of PFC II. Each of Mr. Flint and Mr. McGuire, a member of the Issuer's board of directors, are managing members of PFCM II. Each of PFCM II, Mr. Flint and Mr. McGuire may be deemed to have shared voting, investment and dispositive power with respect to the shares held by PFC II. Percentage based on 18,442,154 shares of Common Stock, which consists of (i) 14,752,689 shares of Common Stock outstanding as of November 1, 2024, as set forth in the Form 10-Q plus (ii) 3,689,465 shares of Common Stock sold by the Issuer in the Private Placement, as set forth in the Form 8-K. Common Stock, $0.0001 par value per share. Tectonic Therapeutic, Inc. 490 Arsenal Way Suite 210 Watertown MA 02472 Explanatory Note: This Amendment No. 1 (this "Amendment") amends and supplements the Schedule 13D originally filed by the Reporting Persons with the Commission on June 25, 2024 (the "Original Schedule 13D"). Only those items that are hereby reported are amended; all other items reports in the Original Schedule 13D remain unchanged. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Capitalized terms not defines in this Amendment have the meanings ascribed to them in the Original Schedule 13D. This Amendment is being filed to update the aggregate percentage of Common Stock owned by the Reporting Persons due to dilution caused by the Issuer's sale of additional shares of its Common Stock from time to time since the date of the filing of the Original Schedule 13D. Such transactions resulted in a decrease of over one percent (1%) in the aggregate ownership reported by the Reporting Persons in the Original Schedule 13D. To Come To Come To Come To Come To Come To Come To Come Solely on behalf of, and only to the extent that it relates to, the Reporting Persons, Item 4 of the Original Schedule 13D is hereby amended and supplemented by the addition of the following: The Reporting Persons have previously reserved the right and continue to reserve the right, based on all relevant factors and subject to applicable law or other restrictions, at any time and from time to time, to acquire additional shares of Common Stock or other securities of the Issuer, dispose of some or all of the shares of Common Stock or other securities of the Issuer that it may own from time to time, in each case in open market or private transactions, block sales or otherwise or pursuant to ordinary stock exchange transactions effected through one or more broker-dealers whether individually or utilizing specific pricing or other instructions (including by means of Rule 10b5-1 programs), and review or reconsider their position, change their purpose, take other actions or formulate and implement plans or proposals with respect to any of the foregoing. The Reporting Persons intend to review their investment in the Issuer from time to time on the basis of various factors, including the Issuer's business, financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer's stock in particular, as well as other developments. See Items 7-11 and 13 of the cover pages of this Amendment for each Reporting Person and the corresponding comments. See Items 7-11 and 13 of the cover pages of this Amendment for each Reporting Person and the corresponding comments. To Come To Come To Come To Come Terrance McGuire /s/ Lauren Crockett* Lauren Crockett/Attorney-in-Fact 02/07/2025 Polaris Partners IX, L.P. /s/ Lauren Crockett Lauren Crockett/General Counsel of Polaris Partners GP IX, L.L.C. the General Partner of Polaris Partners IX, L.P. 02/07/2025 Polaris Partners GP IX, L.L.C. /s/ Lauren Crockett Lauren Crockett/General Counsel 02/07/2025 Polaris Founders Capital Fund I, L.P. /s/ Gregg Rubin Gregg Rubin/General Partner of Polaris Founders Capital Management Co. I, L.L.C. the General Partner of Polaris Founders Capital Fund I, L.P. 02/07/2025 Polaris Founders Capital Fund Management Co. I, L.L.C. /s/ Gregg Rubin Gregg Rubin/General Partner 02/07/2025 Polaris Founders Capital Fund II, L.P. /s/ Harold Friedman Harold Friedman/Vice President of Polaris Founders Capital Management Co. II, L.L.C. the General Partner of Polaris Founders Capital Fund II, L.P. 02/07/2025 Polaris Founders Capital Fund Management Co. II, L.L.C. /s/ Harold Friedman Harold Friedman/Vice President 02/07/2025 Jonathan Flint /s/ Lauren Crockett* Lauren Crockett/Attorney-in-Fact 02/07/2025 [* This Amendment was executed pursuant to a Power of Attorney. Note that copies of the applicable Powers of Attorney are already on file with the appropriate agencies.]