Debt (Tables)

3 Months Ended

Mar. 29, 2026

Debt Disclosure [Abstract]

Schedule of Debt Instruments

Debt at March 29, 2026 and December 28, 2025 was as follows (in millions): 

	March 29, 2026		December 28, 2025
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
ABL Term Loan	200.0		200.0
U.S. revolving credit facility	75.0		—
Foreign credit facilities	1.0		—
Finance leases and other	112.8		111.0
Debt issuance costs	(10.9)		(11.6)
Debt	1,827.9		1,749.4
Short-term debt and current portion of long-term debt	33.2		31.1
Long-term debt	$	1,794.7	$	1,718.3