Debt (Tables)

9 Months Ended

Sep. 28, 2025

Debt Disclosure [Abstract]

Schedule of Debt Instruments

Debt at September 28, 2025 and December 29, 2024 was as follows (in millions): 

	September 28, 2025		December 29, 2024
ATI Inc. 7.25% Notes due 2030	$	425.0	$	425.0
ATI Inc. 5.875% Notes due 2027	350.0		350.0
ATI Inc. 5.125% Notes due 2031	350.0		350.0
ATI Inc. 4.875% Notes due 2029	325.0		325.0
Allegheny Ludlum 6.95% Debentures due 2025 (a)	150.0		150.0
ABL Term Loan	200.0		200.0
U.S. revolving credit facility	—		—
Foreign credit facilities	11.4		—
Finance leases and other	107.7		109.5
Debt issuance costs	(12.2)		(14.2)
Debt	1,906.9		1,895.3
Short-term debt and current portion of long-term debt	191.7		180.4
Long-term debt	$	1,715.2	$	1,714.9

(a) The payment obligations of these debentures issued by Allegheny Ludlum, LLC are fully and unconditionally guaranteed by ATI.