X0609 4 2026-10-13 0001653087 Alector, Inc. ALEC 0001757770 Rosenthal Arnon false C/O ALECTOR, INC. 131 OYSTER POINT BLVD., SUITE 600 SOUTH SAN FRANCISCO CA 94080 true true false false Chief Executive Officer false Common Stock 2026-10-14 4 A false 217500 0 A 2512100 D Common Stock 922875 I See footnote Common Stock 1002500 I See footnote Common Stock 1002500 I See footnote Common Stock 1002500 I See footnote Employee Stock Option (right to buy) 8.16 2026-10-13 4 D false 500000 D 2028-07-01 Common Stock 500000 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 500000 A 2028-07-01 Common Stock 500000 500000 D Employee Stock Option (right to buy) 10.14 2026-10-13 4 D false 275000 D 2028-11-05 Common Stock 275000 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 275000 A 2028-11-05 Common Stock 275000 275000 D Employee Stock Option (right to buy) 17.15 2026-10-13 4 D false 520000 D 2029-11-05 Common Stock 520000 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 520000 A 2029-11-05 Common Stock 520000 520000 D Employee Stock Option (right to buy) 10.24 2026-10-13 4 D false 457038 D 2030-09-30 Common Stock 457038 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 457038 A 2030-09-30 Common Stock 457038 457038 D Employee Stock Option (right to buy) 23.70 2026-10-13 4 D false 417213 D 2031-09-30 Common Stock 417213 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 417213 A 2031-09-30 Common Stock 417213 417213 D Employee Stock Option (right to buy) 9.46 2026-10-13 4 D false 119446 D 2032-09-30 Common Stock 119446 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 119446 A 2032-09-30 Common Stock 119446 119446 D Employee Stock Option (right to buy) 6.48 2026-10-13 4 D false 132500 D 2033-09-30 Common Stock 132500 0 D Employee Stock Option (right to buy) 1.87 2026-10-13 4 A false 132500 A 2033-09-30 Common Stock 132500 132500 D Employee Stock Option (right to buy) 1.88 2026-10-14 4 A false 978750 0 A 2036-10-13 Common Stock 978750 978750 D The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on December 1, 2026. 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. The shares subject to the option are fully vested and immediately exercisable. The transactions reported herein reflect a one-time stock option repricing (the "Option Repricing") effective on October 13, 2026 (the "Effective Date"). The Option Repricing applies to stock options with exercise prices greater than $1.87 per share held by all continuing employees of the Issuer as of the Effective Date. Pursuant to the Option Repricing, the exercise price of the repriced options, including the reported option, has been amended to reduce the exercise price to $1.87 per share, the closing price of the Issuer's common stock on the Effective Date. However, if an employee exercises a repriced Eligible Option before the end of a "Retention Period" that begins on the Effective Date of the Option Repricing and ends on the earliest to occur of the following: (i) one year following the Effective Date; (ii) a Change in Control, as defined in the Issuer's 2019 Equity Incentive Plan, as amended (the "2019 Plan"); and (iii) the optionholder's death or Disability (as defined in the 2019 Plan), then the employee will be required to pay a premium exercise price that is equal to the original exercise price per share of such option. There was no change to the vesting schedules, expiration dates or number of shares underlying the repriced options. Shares subject to the option vest in 48 equal monthly installments beginning on November 1, 2023. Shares subject to the option vest in 48 equal monthly installments beginning on November 13, 2026. /s/ Grace Wong-Sarad, by power of attorney 2026-10-15