X0306 4 2022-10-01 0 0001653087 Alector, Inc. ALEC 0001757770 Rosenthal Arnon C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 1 1 0 0 Chief Executive Officer Common Stock 2022-10-01 4 A 0 179169 0.00 A 1634395 D Common Stock 1972875 I See footnote Common Stock 652500 I See footnote Common Stock 652500 I See footnote Common Stock 652500 I See footnote Employee Stock Option (right to buy) 9.46 2022-10-01 4 A 0 119446 0.00 A 2032-10-01 Common Stock 119446 119446 D The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on March 1, 2023. The reported securities are held directly by The Rosenthal Family Revocable Trust Dated November 4, 1994, as restated on June 9, 1999, for which the Reporting Person serves as trustee. The reported securities are held directly by the Adi Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee. The reported securities are held directly by the Noam Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee. The reported securities are held directly by the Shani Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee. Shares subject to the option vest in 48 equal monthly installments beginning on November 1, 2022. Exhibit 24 - Power of Attorney /s/ Marc Grasso, by power of attorney 2022-10-04