Accumulated Other Comprehensive Income (Loss) (Tables)

3 Months Ended

Mar. 29, 2026

Equity [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss)

The changes in AOCI by component, net of tax, for the quarter ended March 29, 2026 were as follows (in millions):

	Post- retirement benefit plans		Currency translation adjustment		Derivatives		Deferred Tax Asset Valuation Allowance		Total
Attributable to ATI:
Balance, December 28, 2025	$	(32.2)	$	(52.1)	$	0.6	$	23.3	$	(60.4)
OCI before reclassifications		—		(3.1)		1.8		—	(1.3)
Amounts reclassified from AOCI	(a)	1.0		—	(b)	(2.2)		—	(1.2)
Net current-period OCI		1.0		(3.1)		(0.4)		—	(2.5)
Balance, March 29, 2026	$	(31.2)	$	(55.2)	$	0.2	$	23.3	$	(62.9)
Attributable to noncontrolling interests:
Balance, December 28, 2025	$	—	$	12.0	$	—	$	—	$	12.0
OCI before reclassifications		—		1.3		—		—	1.3
Amounts reclassified from AOCI		—		—		—		—	—
Net current-period OCI		—		1.3		—		—	1.3
Balance, March 29, 2026	$	—	$	13.3	$	—	$	—	$	13.3

(a)Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 12).

(b)Amounts related to derivatives are included in sales, cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 9).

The changes in AOCI by component, net of tax, for the quarter ended March 30, 2025 were as follows (in millions):

	Post- retirement benefit plans		Currency translation adjustment		Derivatives		Deferred Tax Asset Valuation Allowance		Total
Attributable to ATI:
Balance, December 29, 2024	$	(30.5)	$	(79.8)	$	(2.5)	$	23.3	$	(89.5)
OCI before reclassifications		—		6.2		4.9		—	11.1
Amounts reclassified from AOCI	(a)	0.9	(b)	5.1	(d)	0.8	(e)	—	6.8
Net current-period OCI		0.9		11.3		5.7		—	17.9
Balance, March 30, 2025	$	(29.6)	$	(68.5)	$	3.2	$	23.3	$	(71.6)
Attributable to noncontrolling interests:
Balance, December 29, 2024	$	—	$	5.7	$	—	$	—	$	5.7
OCI before reclassifications		—		1.2		—		—	1.2
Amounts reclassified from AOCI		—	(c)	—		—		—	—
Net current-period OCI		—		1.2		—		—	$	1.2
Balance, March 30, 2025	$	—	$	6.9	$	—	$	—	$	6.9

(a)Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 12).

(b)Amounts were included in gain/loss of asset sales and sales of businesses, net, as part of the loss on sale of the Birmingham, UK and Dusseldorf, Germany operations (see Note 5).

(c)No amounts were reclassified to earnings.

(d)Amounts related to derivatives are included in sales, cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 9).

(e)Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates.

Schedule of Reclassifications Out of AOCI

Reclassifications out of AOCI for the quarters ended March 29, 2026 and March 30, 2025 were as follows: 

Details about AOCI Components (In millions)	Three months ended March 29, 2026		Three months ended March 30, 2025			Affected line item in the statements of operations
Postretirement benefit plans
Prior service credit	$	(0.1)	0.1		(a)
Actuarial losses	(1.3)		(1.3)		(a)
	(1.4)		(1.2)		(d)	Total before tax
	(0.4)		(0.3)			Tax benefit (e)
	$	(1.0)	$	(0.9)		Net of tax
Currency translation adjustment	$	—	$	(5.1)	(b,d)
Derivatives
Nickel and other raw material contracts	$	0.5	$	(1.3)	(c)
Natural gas contracts	2.1		0.2		(c)
Foreign exchange contracts	0.3		0.1		(c)
Interest rate swap	—		—		(c)
	2.9		(1.0)		(d)	Total before tax
	0.7		(0.2)			Tax benefit (e)
	$	2.2	$	(0.8)		Net of tax

(a)Amounts are reported in nonoperating retirement benefit expense (see Note 12).

(b)Amounts in 2025 were included in gain/loss on asset sales and sales of businesses, net, as part of the loss on sale of the Birmingham, UK and Dusseldorf, Germany operations (see Note 5).

(c)Amounts related to derivatives, with the exception of the interest rate swap, are included in sales or cost of goods sold in the period or periods the hedged item affects earnings. Amounts related to the interest rate swap are included in interest expense in the same period as the interest expense on the Term Loan is recognized in earnings (see Note 9).

(d)For pre-tax items, positive amounts are income and negative amounts are expense in terms of the impact to net income. Tax effects are presented in conformity with ATI’s presentation in the consolidated statements of operations.

(e)These amounts exclude the impact of any deferred tax asset valuation allowances, when applicable.