X0609 4 2026-08-17 0001018963 ATI INC ATI 0001773072 Fields Kimberly A false C/O ATI INC. 2021 MCKINNEY AVE., SUITE 1100 DALLAS TX 75201 true true false false Chair, President and CEO true Common Stock, par value $0.10 per share 2026-08-17 4 S false 1000 228.32 D 124564 D Common Stock, par value $0.10 per share 2026-08-17 4 S false 2000 229.56 D 122564 D Common Stock, par value $0.10 per share 2026-08-17 4 S false 8131 230.66 D 114433 D Common Stock, par value $0.10 per share 2026-08-17 4 S false 9116 231.72 D 105317 D Common Stock, par value $0.10 per share 2026-08-17 4 S false 4598 232.43 D 100719 D Shares sold pursuant to a 10b5-1 Trading Plan dated February 5, 2026, entered into for personal tax and estate planning purposes. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $228.02 to $228.73. The reporting person undertakes to provide to the Issuer, its security holders and the Staff of the SEC, upon request, full information regarding the number of shares sold at each specific price within the range reported. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $229.14 to $230.07. The reporting person undertakes to provide to the Issuer, its security holders and the Staff of the SEC, upon request, full information regarding the number of shares sold at each specific price within the range reported. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $230.17 to $231.16. The reporting person undertakes to provide to the Issuer, its security holders and the Staff of the SEC, upon request, full information regarding the number of shares sold at each specific price within the range reported. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $231.20 to $232.18. The reporting person undertakes to provide to the Issuer, its security holders and the Staff of the SEC, upon request, full information regarding the number of shares sold at each specific price within the range reported. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $232.19 to $232.74. The reporting person undertakes to provide to the Issuer, its security holders and the Staff of the SEC, upon request, full information regarding the number of shares sold at each specific price within the range reported. /s/ Amanda J. Skov, Attorney-in-Fact for Kimberly A. Fields 2026-08-19