X0407 4 2023-05-09 0 0001962918 ACELYRIN, Inc. SLRN 0001973851 Oyston Ronald C/O ACELYRIN, INC. 4149 LIBERTY CANYON RD. AGOURA HILLS CA 91301 0 1 0 0 Chief People Officer 0 Common Stock 2023-05-09 4 P 0 1000 18.00 A 1000 D Common Stock 2023-05-09 4 P 0 26 18.00 A 26 I See footnote Employee Stock Option (right to buy) 4.0426 2023-05-09 4 J 0 165090 0.00 D 2032-01-19 Class A Common Stock 165090 0 D Employee Stock Option (right to buy) 4.0426 2023-05-09 4 J 0 165090 0.00 A 2032-01-19 Common Stock 165090 165090 D Employee Stock Option (right to buy) 4.0426 2023-05-09 4 J 0 2150 0.00 D 2032-01-19 Class A Common Stock 2150 0 D Employee Stock Option (right to buy) 4.0426 2023-05-09 4 J 0 2150 0.00 A 2032-01-19 Common Stock 2150 2150 D Employee Stock Option (right to buy) 5.8766 2023-05-09 4 J 0 23412 0.00 D 2032-11-20 Class A Common Stock 23412 0 D Employee Stock Option (right to buy) 5.8766 2023-05-09 4 J 0 23412 0.00 A 2032-11-20 Common Stock 23412 23412 D Employee Stock Option (right to buy) 5.8766 2023-05-09 4 J 0 16613 0.00 D 2032-11-20 Class A Common Stock 16613 0 D Employee Stock Option (right to buy) 5.8766 2023-05-09 4 J 0 16613 0.00 A 2032-11-20 Common Stock 16613 16613 D Employee Stock Option (right to buy) 18.00 2023-05-09 4 J 0 131714 0.00 D 2033-05-03 Class A Common Stock 131714 0 D Employee Stock Option (right to buy) 18.00 2023-05-09 4 J 0 131714 0.00 A 2033-05-03 Common Stock 131714 131714 D Reflects shares purchased through a directed share program in the Issuer's initial public offering of Common Stock (the "IPO"). The shares are held of record by the Reporting Person's child. Each share of Class A Common Stock was reclassified into one share of Common Stock immediately prior to the completion of the IPO. 1/4 of the shares subject to the option vested on November 1, 2022, and 1/48 of the shares subject to the option vests in equal monthly installments thereafter, subject to the Reporting Person's continued service. 1/4 of the shares subject to the option vested on January 20, 2023, and 1/48 of the shares subject to the option vest in equal monthly installments thereafter, subject to the Reporting Person's continued service. 1/4 of the shares subject to the option vest on October 1, 2023, and 1/48 of the shares subject to the option vests in equal monthly installments thereafter, subject to the Reporting Person's continued service. 1/4 of the shares subject to the option vest on November 17, 2023, and 1/48 of the shares subject to the option vests in equal monthly installments thereafter, subject to the Reporting Person's continued service. 1/4 of the shares subject to the option vest on May 4, 2024, and 1/48 of the shares subject to the option vest in equal monthly installments thereafter, subject to the Reporting Person's continued service. /s/ Mina Kim, Attorney-in-fact 2023-05-11