X0508 4 2024-12-02 0001653087 Alector, Inc. ALEC 0001748894 GRASSO MARC C/O ALECTOR, INC. 131 OYSTER POINT BLVD., SUITE 600 SOUTH SAN FRANCISCO CA 94080 false true false false Chief Financial Officer false Common Stock 2024-12-02 4 S false 16489 2.5194 D 330651 D 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 $2.5193 to $2.5195. 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/ Marc Grasso 2024-12-03