144 0001635153 XXXXXXXX LIVE 0001018963 ATI INC 001-12001 2021 McKinnery Avenue Dallas TX 75201 800-289-7454 Morehouse David J Director Common Morgan Stanley

1300 Thames Street Thames Street Whart, 5th Floor Baltimore MD 21231

6609 1019483 136936299 03/09/2026 NYSE Common 05/10/2019 Restricted stock vesting Issuer N 1513 05/10/2019 Director compensation Common 05/14/2019 Restricted stock vesting Issuer N 3526 05/14/2019 Director compesnation Common 05/13/2020 Restricted stock vesting Issuer N 1561 05/13/2020 Director compensation Y 03/11/2026 Amanda J. Skov, Attorney in Fact for David J. Morehouse