X0609 4 2026-09-02 0001653087 Alector, Inc. ALEC 0002074667 Wong-Sarad Grace false C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 false true false false Principal Accounting Officer false Common Stock 2026-09-02 4 S false 656 2.75 D 114805 D Common Stock 2026-09-03 4 S false 5165 2.6655 D 109640 D Common Stock 2026-09-04 4 S false 3625 2.5088 D 106015 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025. The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.49 to $2.75. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.495 to $2.52. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request. /s/Grace Wong-Sarad 2026-09-04