X0306 4 2023-02-23 0 0001018963 ATI INC ATI 0001572385 WETHERBEE ROBERT S 2021 MCKINNEY AVENUE SUITE 1100 DALLAS TX 75201 1 1 0 0 Board Chair, President and CEO Common Stock, par value $0.10 per share 2023-02-23 4 A 0 44793 0.00 A 376675.3409 D Common Stock, par value $0.10 per share 2023-02-23 4 F 0 18757 40.51 D 357918.3409 D Common Stock, par value $0.10 per share 2023-02-24 4 F 0 8616 39.45 D 349302.3409 D Settlement of performance-vested restricted stock units that were granted in 2020, the vesting of which was contingent upon the Issuer's achievement of specified performance criteria during the period from January 1, 2020 through December 31, 2022 (the "2020-2022 PSUs"). The shares underlying the 2020-2022 PSUs became payable as of February 23, 2023 following certification of the Issuer's achievement of such performance criteria by the Personnel and Compensation Committee of the Issuer's Board of Directors. Shares withheld for payment of taxes in connection with the February 23, 2022 settlement of the 2020-2022 PSUs. Represents the average of the high and low trading prices for one share of the Issuer's common stock on the New York Stock Exchange on February 23, 2023. Shares withheld for payment of taxes on restricted stock units awarded on February 24, 2020. One-third of such restricted stock units vested by their terms on February 24, 2023. Represents the average of the high and low trading prices for one share of the Issuer's common stock on the New York Stock Exchange on February 24, 2023. /s/ Elliot S. Davis, Attorney-in-Fact for Robert S. Wetherbee 2023-02-27