X0202 SCHEDULE 13G/A 0001493463 XXXXXXXX LIVE 7 Common Stock, $0.0001 par value per share 03/31/2026 0001653087 Alector, Inc. 014442107 131 OYSTER POINT BLVD. SUITE 600 SOUTH SAN FRANCISCO CA 94080 Rule 13d-1(d) Polaris Venture Partners VI, L.P. b DE 498468 0 498468 0 498468 N 0.5 PN All shares are held of record by PVP VI (as defined in Item 2(a) of the Original Schedule 13G (as defined below)). PVM VI (as defined in Item 2(a) of the Original Schedule 13G), the general partner of PVP VI, may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of the Issuer's common stock ("Common Stock") outstanding as of February 20, 2026, as set forth in the Issuer's annual report on Form 10-K for the year ended December 31, 2026, filed with the United States Securities and Exchange Commission (the "Commission") on February 25, 2026 (the "Form 10-K"). Polaris Venture Partners Founders' Fund VI, L.P. b DE 267979 0 267979 0 267979 N 0.2 PN All shares are held of record by PVPFF VI (as defined in Item 2(a) of the Original Schedule 13G). PVM VI, the general partner of PVPFF VI, may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Polaris Venture Partners VI (AIV), L.P. b DE 3280842 0 3280842 0 3280842 N 3.0 PN All shares are held of record by PVP VI (AIV) (as defined in Item 2(a) of the Original Schedule 13G). PVM VI, the general partner of PVP VI (AIV), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Polaris Venture Partners VI (AIV-B), L.P. b DE 806528 0 806528 0 806528 N 0.7 PN All shares are held of record by PVP VI (AIV-B) (as defined in Item 2(a) of the Original Schedule 13G). PVM VI, the general partner of PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Polaris Venture Management Co VI, L.L.C. b DE 0 4853817 0 4853817 4853817 N 4.4 OO The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. David Barrett b X1 0 4853817 0 4853817 4853817 N 4.4 IN The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Brian Chee b X1 0 4853817 0 4853817 4853817 N 4.4 IN The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Jonathan A. Flint b X1 39124 4853817 39124 4853817 4892941 N 4.4 IN The shares reported in Rows 5 and 7 are held directly by Jonathan A. Flint. The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Terrance G. McGuire b X1 319682 4853817 319682 4853817 5173499 N 4.7 IN The shares reported in Rows 5 and 7 consist of (i) 96,435 shares held directly by Terrance G. McGuire, (ii) 196,997 shares held by McGuire Family Trust, and (iii) 26,250 shares consist of restricted stock units that have been granted to Terrance G. McGuire in his capacity as a former director of the Issuer. Terrance G. McGuire is the donor of the McGuire Family Trust and may be deemed to share voting, investment and dispositive power with respect to the shares held by the McGuire Family Trust. The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,388,831 shares of Common Stock, calculated as follows: (i) 26,250 shares that represent restricted stock units that have been granted to Mr. McGuire in his capacity as a former director of the Issuer plus (ii) 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Amir Nashat b X1 131332 4853817 131332 4853817 4985149 N 4.5 IN The shares reported in Rows 5 and 7 are held directly by Amir Nashat. The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Bryce Youngren b X1 11864 4853817 11864 4853817 4865681 N 4.4 IN The shares reported in Rows 5 and 7 are held directly by Bryce Youngren. The shares reported in Rows 6 and 8 consist of (i) 498,468 shares held of record by PVP VI, (ii) 267,979 shares held of record by PVPFF VI, (iii) 3,280,842 shares held of record by PVP VI (AIV) and (iv) 806,528 shares held of record by PVP VI (AIV-B). PVM VI, the general partner of each of PVP VI, PVPFF VI, PVP VI (AIV) and PVP VI (AIV-B), may be deemed to have voting, investment and dispositive power with respect to these securities. David Barrett, Brian Chee, Jonathan A. Flint, Terrance G. McGuire, Amir Nashat, and Bryce Youngren are the managing members of PVM VI and may each be deemed to share voting, investment and dispositive power with respect to these securities. The percentage in Row 11 is based on 110,362,581 shares of Common Stock outstanding as of February 20, 2026, as set forth in the Form 10-K. Alector, Inc. 131 OYSTER POINT BLVD., SUITE 600, SOUTH SAN FRANCISCO, CA, 94080 This Amendment No. 7 (this "Amendment") amends and supplements the Schedule 13G initially filed with the Commission on February 12, 2020, as amended by Amendment No. 1 filed with the Commission on February 12, 2021, Amendment No. 2 filed with the Commission on February 11, 2022, Amendment No. 3 filed with the Commission on February 7, 2023, Amendment No. 4 filed with the Commission on February 9, 2024, Amendment No. 5 filed with the Commission on November 12, 2024, and Amendment No. 6 filed with the Commission on November 13, 2025 (collectively, the "Original Schedule 13G"). Only those items that are hereby reported are amended; all other items reported in the Original Schedule 13G remain unchanged. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Capitalized terms not defined in this Amendment have the meanings ascribed to them in the Original Schedule 13G. The following information in Item 4 with respect to the ownership of the Issuer's Common Stock by the Reporting Persons filing this Amendment No. 7 is provided as of April 30, 2026. Each of the Reporting Persons disclaims beneficial ownership of the shares of Common Stock reported in this Amendment No. 7, except for the shares, if any, such Reporting Person holds of record and to the extent of such Reporting Person's pecuniary interest therein. N See Row 9 of cover page for each Reporting Person and the corresponding footnotes. See Row 11 of cover page for each Reporting Person and the corresponding footnotes. See Row 5 of cover page for each Reporting Person and the corresponding footnotes. See Row 6 of cover page for each Reporting Person and the corresponding footnotes. See Row 7 of cover page for each Reporting Person and the corresponding footnotes. See Row 8 of cover page for each Reporting Person and the corresponding footnotes. N Y N N N N Y Polaris Venture Partners VI, L.P. /s/ Lauren Crockett 05/14/2026 Polaris Venture Partners Founders' Fund VI, L.P. /s/ Lauren Crockett 05/14/2026 Polaris Venture Partners VI (AIV), L.P. /s/ Lauren Crockett 05/14/2026 Polaris Venture Partners VI (AIV-B), L.P. /s/ Lauren Crockett 05/14/2026 Polaris Venture Management Co VI, L.L.C. /s/ Lauren Crockett 05/14/2026 David Barrett /s/ Lauren Crockett 05/14/2026 Brian Chee /s/ Lauren Crockett 05/14/2026 Jonathan A. Flint /s/ Lauren Crockett 05/14/2026 Terrance G. McGuire /s/ Lauren Crockett 05/14/2026 Amir Nashat /s/ Lauren Crockett 05/14/2026 Bryce Youngren /s/ Lauren Crockett 05/14/2026 This Schedule 13G was executed pursuant to a Power of Attorney. Note that copies of the applicable Power of Attorney are already on file with the appropriate agencies.