Debt (Tables)

12 Months Ended

Dec. 28, 2025

Debt Disclosure [Abstract]

Schedule of Debt

Debt at December 28, 2025 and December 29, 2024 was as follows:

	Fiscal Year
(In millions)	2025		2024
ATI Inc. 7.25% Senior Notes due 2030	$	425.0	$	425.0
ATI Inc. 5.875% Senior Notes due 2027	350.0		350.0
ATI Inc. 5.125% Senior Notes due 2031	350.0		350.0
ATI Inc. 4.875% Senior Notes due 2029	325.0		325.0
Allegheny Ludlum 6.95% Debentures due 2025 (a)	—		150.0
ABL Term Loan	200.0		200.0
U.S. revolving credit facility	—		—
Foreign credit agreements	—		—
Finance leases and other	111.0		109.5
Debt issuance costs	(11.6)		(14.2)
Total short-term and long-term debt	1,749.4		1,895.3
Short-term debt and current portion of long-term debt	31.1		180.4
Total long-term debt	$	1,718.3	$	1,714.9

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

Schedule of Interest Income Expense

Interest expense on the 2025 Convertible Notes was as follows:

	Fiscal Year
(in millions)	2024		2023
Contractual coupon rate	$	7.2	$	10.2
Amortization of debt issuance costs	1.3		1.9
Total interest expense	$	8.5	$	12.1