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Earnout Liability - Additional Information (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024 CAD ($) shares	Dec. 31, 2025 CAD ($) shares	Dec. 31, 2025 $ / shares shares
Earnout Liability [Line Items]
Earnout shares outstanding			655,453
Earnout shares fair value per share \| $ / shares			$ 4.1
Loss (gain) on earn out liability \| $	$ 5.3	$ 19.8
Earnout share vested and settled	(320,000)	(75,000)
Earn out rights forfeited and cancelled	172,786	75,000

Dividends (Tables)

12 Months Ended

Dec. 31, 2025

Disclosure of Detailed Information About Dividends [Abstract]

Summary of Dividends


Record date	Payment date	Total Dividends on Common Stock
March 21, 2025	April 10, 2025	$	7.5
May 13, 2025	May 30, 2025		7.3

		$	14.8

Accounts Payable and Accrued Liabilities

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Accounts Payable and Accrued Liabilities

19.	ACCOUNTS PAYABLE AND ACCRUED LIABILITIES


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Accounts payable	$	47.7	$	146.1

Accrued liabilities		109.5		121.1

Wages and accrued vacation payable		46.7		51.9


	$	203.9	$	319.1

Bank Indebtedness

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Bank Indebtedness

18.	BANK INDEBTEDNESS

The Company increased its traditional asset-based revolving credit facility (“Revolving Credit Facility”) from US $300.0 million to US $375.0 million on September 12, 2025, maturing May, 2028. The Revolving Credit Facility is secured by substantially all of the Company’s assets. Under the General Security Agreement, the Revolving Credit Facility has a priority claim on the accounts receivable and the inventories of the Company and the rest of the Company’s assets. The Revolving Credit Facility contains a customary springing fixed charge coverage ratio when availability falls below a certain ratio. The interest rate on the Revolving Credit Facility is based on Secured Overnight Financing Rate (“SOFR”) plus a credit spread adjustment of 10 basis points plus an applicable margin, which varies depending on usage.

At December 31, 2025, the Company had drawn $170.2 million (US $124.2 million), and there was $194.5 million (US $141.9 million) of unused availability after taking into account $66.1 million (US $48.2 million) of outstanding letters of credit, and borrowing base reserves. At December 31, 2024, the Company had drawn $0.4 million (US $0.3 million), and there was $361.8 million (US $251.4 million) of unused availability after taking into account $69.5 million (US $48.3 million) of outstanding letters of credit and borrowing base reserves.

Transaction costs related to the Revolving Credit Facility amounted to $8.7 million. Transaction costs are disclosed as other

non-current

assets in the consolidated statements of financial position, and have been amortized on a straight-line basis over the life of this facility, which has a maturity date of May 31, 2028. At December 31, 2025, the unamortized transaction costs related to the Revolving Credit Facility were $0.8 million (December 31, 2024 - $1.1 million).

Reconciliation of liabilities arising from financing activities

The changes in the Company’s bank indebtedness for the year ended December 31, 2025 and nine month period ended December 31, 2024 arising from financing activities are presented below:


Balance at March 31, 2024	$	0.3

Revolving Credit Facility drawn		3.0

Repayment of Revolving Credit Facility		(2.9	)



Balance at December 31, 2024	$	0.4

Revolving Credit Facility drawn		213.9

Repayment of Revolving Credit Facility		(42.4	)

Foreign exchange		(1.7	)

Balance at December 31, 2025	$	170.2

Other Long-Term Liabilities - Additional Information (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Sep. 03, 2025	Jul. 24, 2025	Dec. 07, 2023
Disclosure of Detailed about Other Long term Liabilities [Line Items]
Cash consideration of financing arrangement				$ 5.1	$ 10.4	$ 11.7
Monthly Interest Payables For Financing Arrangement					$ 0.1	$ 0.1
Repayments of borrowings	$ 0.7	$ 0.2	$ 0.0
Loan Interest		$ 38.6	$ 0.0
Monthly interest payable for instalment payment contract				$ 0.1

Financial Instruments - Summary of Company's Contractually Agreed (Undiscounted) Cash Flows Payable Under Financial Liabilities (Detail) $ in Millions	Dec. 31, 2025 CAD ($)
Maturity Analysis For Financial Liabilities [Line Items]
Governmental Loans	$ 206.3
Financial arrangement	24.5
Senior Secured Lien Notes	476.6
Interest on Senior Secured Lien Notes	0.0
Government Loans, undiscounted cash flows	(292.4)
Interest on Provincial MENDM Loan, undiscounted cash flows	0.0
Financial arrangement, undiscounted cash flows	0.0
Senior Secured Lien Notes, undiscounted cash flows	(479.7)
Interest on senior secured lien notes, undiscounted cash flows	(65.7)
Financial liabilities, undiscounted cash flows	$ (292.4)

Share-Based Payment Compensation Liability - Summary Of Continuity of Replacement LTIP Units (Detail) - shares	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025	Mar. 31, 2025
Replacement Long Term Incentive Plan Awards [Line Items]
Dividend equivalents and other adjustments	4,941	7,124	43,127

Revenue - Additional Information (Detail) - Customer	9 Months Ended	12 Months Ended
Revenue - Additional Information (Detail) - Customer	Dec. 31, 2024	Dec. 31, 2025
Disclosure Of Revenue [Line Items]
Number of customer over ten percent revenue benchmark	1	1

Other Post-Employment Benefits

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Other Post-Employment Benefits

24.	OTHER POST-EMPLOYMENT BENEFITS

The Company offers post-employment life insurance, health care and dental care to some of its retirees. These obligations are not

pre-funded.

The most recent actuarial valuations of the present value of the other post-employment benefit obligation were carried out at November 1, 2025.

The principal assumptions used for the purposes of the actuarial valuations were as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Assumptions for determination of defined benefit cost:

Discount rate

Defined benefit obligation		4.70%		4.85%

Current service cost		4.81%		4.84%

Interest cost on benefit obligation		4.39%		4.79%

Interest cost on current service cost		4.80%		4.85%

Health care cost immediate trend rate		4.83%		4.90%

Assumptions for determination of defined benefit obligation:

Effective discount rate		4.98%		4.70%

Health care cost immediate trend rate		4.76%		4.83%

Assumptions for determination of defined benefit cost and defined benefit obligation:

Health care cost ultimate trend rate		4.00%		4.00%

Year ultimate health care cost trend rate reached		2040		2040

Salary Increases per annum		2.00%		2.00%

Mortality		105%CPM 2014 Private Projection CPM-B		105%CPM 2014 Private Projection CPM-B

The components of amounts recognized in the consolidated statements of net loss in respect of the

other

post-employment benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in net loss were as follows:

Current service cost	$	3.3	$	2.4

Past service cost		(6.0)		-

Net interest cost		8.8		8.0


	$	6.1	$	10.4


Post employment benefit costs recognized in:

Cost of sales	$	(2.5)	$	2.1

Administrative and selling expenses		(0.2)		0.3

Interest on other post-employment benefit obligation		8.8		8.0


	$	6.1	$	10.4

Past service cost recognition

On December 1, 2025 the Company issued 1,005 layoff notices to unionized employees which caused a curtailment and resulted in a past service cost adjustment related to the other post-employment benefit plan of $6.0 million, of which $5.4 million was recorded in cost of steel revenue and $0.6 million was recorded in administrative and selling expense for the year ended December 31, 2025 (nil for the nine month period ended December 31, 2024).

The amounts recognized in the consolidated statements of other comprehensive (loss) income in respect of these other post-employment benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in other comprehensive loss, were as follows:

Actuarial gain on accrued post employment benefit liability	$	(8.8)	$	(25.3)

The amounts included in the consolidated statements of financial position arising from the Company’s obligation in respect of its other post-retirement benefit plans were as follows:


As at,	December 31, 2025		December 31, 2024

Present value of post-employment benefit obligation	$	193.0	$	206.2
Fair value of plan assets		-		-

Accrued other post-employment benefit obligation	$	193.0	$	206.2

Reconciliation of the amounts recognized in accumulated other comprehensive (loss) income in the consolidated statements of changes in shareholders’ equity were as follows:


	Actuarial (gain) loss immediately recognized			Tax effect		Actuarial (gain) loss immediately recognized, net of tax

Balance at March 31, 2024	$	(73.5	)	$	-	$	(73.5	)

Actuarial gain immediately recognized		(25.3	)		-		(25.3	)


Balance at December 31, 2024	$	(98.8	)	$	-	$	(98.8	)

Actuarial gain immediately recognized		(8.8	)		-		(8.8	)

Balance at December 31, 2025	$	(107.6	)	$	-	$	(107.6	)

Continuities of the other post-employment benefit plan assets and obligations are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Movements in the present value of the post-employment benefit plan assets were as follows:

Fair value of plan assets at beginning of the period and year, respectively	$	-		$	-
Employer contributions		10.6			8.5
Benefits paid		(10.6	)		(8.5	)
Fair value of plan assets at December 31, 2025 and

December 31, 2024, respectively	$	-		$	-


Movements in the present value of the other post-employment benefit obligation were as follows:

Defined benefit obligation at the beginning of the period and year, resepectively	$	206.2		$	229.5
Current service cost		3.3			2.4
Interest cost		8.8			8.0
Past service cost		(6.0	)		-
Actuarial (gains) losses arising from financial assumptions		(5.3	)		3.9
Actuarial gains arising from demographic assumptions		(5.5	)		(33.2	)
Actuarial losses from experience adjustments		2.1			4.1
Benefits paid		(10.6	)		(8.5	)
Defined benefit obligation at December 31, 2025 and

December 31, 2024, respectively	$	193.0		$	206.2

Cash flow information

For the year ended December 31, 2025, the amounts included in the consolidated statements of cash flows in respect of these other post-employment benefit plans was $10.6 million. For the nine month period ended December 31, 2024, the amounts included in the consolidated statements of cash flows in respect of these other post-employment benefit plans was $8.5 million. The Company’s expected contributions for the fiscal year ending December 31, 2026 is $12.6 million.

Sensitivity of results to actuarial assumptions

The sensitivity of the other post-employment benefit obligation to changes in the discount rate, health care cost trend rate and mortality assumptions are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Effect of change in discount rate assumption
One percentage point increase	$	(20.0)	$	(23.9)
One percentage point decrease	$	24.8	$	30.0

Effect of change in health care cost trend rates
One percentage point increase	$	20.2	$	24.0
One percentage point decrease	$	(17.6)	$	(20.5)

Effect of change in mortality assumption
Set forward one year	$	7.9	$	8.6
Set back one year	$	(7.7)	$	(8.4)

The discount rate sensitivities presented above are estimates based on plan durations. The other post-employment benefit obligation and the current service cost have an implied duration of 12 and 28 years, respectively at current discount rates.

Administrative and Selling Expenses (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information About Administrative and Selling Expenses


	Year ended December 31, 2025		Nine months ended December 31, 2024

Administrative and selling expense is comprised of:

Personnel expenses	$	36.6	$	30.5

Share-based compensation expense		7.4		12.7

Professional, consulting, legal and other fees		15.2		14.6

Insurance		35.4		24.6

Software licenses		6.8		5.3

Allowance for doubtful accounts (Note 15)		0.4		5.6

Amortization of intangible assets and non-producing assets		0.8		0.4

Other administrative and selling		9.6		9.9


	$	112.2	$	103.6

Inventories (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Inventories Net Explanatory


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Raw materials and consumables	$	272.7	$	637.8

Work in progress		203.2		147.0

Finished goods		93.4		94.4


	$	569.3	$	879.2

Label	Element	Value
Severance Costs	astl_SeveranceCosts	$ 45,800,000
Severance Costs	astl_SeveranceCosts	0
Gain Loss Change In Fair Value of Initial Public Offering And Large Enterprise Tariff Loan And Warrant Liabilities	astl_GainLossChangeInFairValueOfInitialPublicOfferingAndLargeEnterpriseTariffLoanAndWarrantLiabilities	41,500,000
Gain Loss Change In Fair Value of Initial Public Offering And Large Enterprise Tariff Loan And Warrant Liabilities	astl_GainLossChangeInFairValueOfInitialPublicOfferingAndLargeEnterpriseTariffLoanAndWarrantLiabilities	(4,000,000)
Change in Fair Value of Earnout Liability	astl_ChangeInFairValueOfEarnoutLiability	5,600,000
Change in Fair Value of Earnout Liability	astl_ChangeInFairValueOfEarnoutLiability	(2,400,000)
Change In Fair Value Of Share Based Compensation Liability	astl_ChangeInFairValueOfShareBasedCompensationLiability	19,800,000
Change In Fair Value Of Share Based Compensation Liability	astl_ChangeInFairValueOfShareBasedCompensationLiability	(5,300,000)
Current Liabilities From Share based Payment Transactions	astl_CurrentLiabilitiesFromShareBasedPaymentTransactions	14,100,000
Current Liabilities From Share based Payment Transactions	astl_CurrentLiabilitiesFromShareBasedPaymentTransactions	34,500,000
Accrued Pension Liability	astl_AccruedPensionLiability	153,000,000
Accrued Pension Liability	astl_AccruedPensionLiability	178,300,000
Contributed Surplus Deficit	astl_ContributedSurplusDeficit	(900,000)
Contributed Surplus Deficit	astl_ContributedSurplusDeficit	(7,900,000)
Increase Decrease Through Issuance Performance Share Units And Restricted Share Units	astl_IncreaseDecreaseThroughIssuancePerformanceShareUnitsAndRestrictedShareUnits	4,900,000
Increase Decrease Through Issuance Performance Share Units And Restricted Share Units	astl_IncreaseDecreaseThroughIssuancePerformanceShareUnitsAndRestrictedShareUnits	4,900,000
Increase Decrease Through Issuance Performance Share Units And Restricted Share Units	astl_IncreaseDecreaseThroughIssuancePerformanceShareUnitsAndRestrictedShareUnits	11,400,000
Increase Decrease Through Issuance Performance Share Units And Restricted Share Units	astl_IncreaseDecreaseThroughIssuancePerformanceShareUnitsAndRestrictedShareUnits	11,400,000
Increase Decrease Through Issuance Of Deferred Share Units	astl_IncreaseDecreaseThroughIssuanceOfDeferredShareUnits	2,100,000
Increase Decrease Through Issuance Of Deferred Share Units	astl_IncreaseDecreaseThroughIssuanceOfDeferredShareUnits	2,100,000
Increase Decrease Through Issuance Of Deferred Share Units	astl_IncreaseDecreaseThroughIssuanceOfDeferredShareUnits	1,700,000
Increase Decrease Through Issuance Of Deferred Share Units	astl_IncreaseDecreaseThroughIssuanceOfDeferredShareUnits	1,700,000
Dividend Equivalent	astl_DividendEquivalent	(200,000)
Dividend Equivalent	astl_DividendEquivalent	(200,000)
Dividend Equivalent	astl_DividendEquivalent	(200,000)
Dividend Equivalent	astl_DividendEquivalent	(200,000)
Earnout Out Rights Forfeited	astl_EarnoutOutRightsForfeited	2,300,000
Earnout Out Rights Forfeited	astl_EarnoutOutRightsForfeited	2,300,000
Adjustments For Pension Expense in Excess of Funding Or Pension Funding in Excess of Expense	astl_AdjustmentsForPensionExpenseInExcessOfFundingOrPensionFundingInExcessOfExpense	(6,800,000)
Adjustments For Pension Expense in Excess of Funding Or Pension Funding in Excess of Expense	astl_AdjustmentsForPensionExpenseInExcessOfFundingOrPensionFundingInExcessOfExpense	(8,200,000)
Adjustments For Unrealised Foreign Exchange Losses Gains on Accrued Pension Liability	astl_AdjustmentsForUnrealisedForeignExchangeLossesGainsOnAccruedPensionLiability	(8,100,000)
Adjustments For Unrealised Foreign Exchange Losses Gains on Accrued Pension Liability	astl_AdjustmentsForUnrealisedForeignExchangeLossesGainsOnAccruedPensionLiability	12,900,000
Adjustments For Unrealised Foreign Exchange Losses Gains on Post Employment Benefit Obligations	astl_AdjustmentsForUnrealisedForeignExchangeLossesGainsOnPostEmploymentBenefitObligations	10,000,000
Adjustments For Unrealised Foreign Exchange Losses Gains on Post Employment Benefit Obligations	astl_AdjustmentsForUnrealisedForeignExchangeLossesGainsOnPostEmploymentBenefitObligations	(14,000,000)
Adjustments For Severance Costs	astl_AdjustmentsForSeveranceCosts	45,800,000
Adjustments For Severance Costs	astl_AdjustmentsForSeveranceCosts	0
Adjustments For Interest on Pension and Other Post Employment Benefit Obligations	astl_AdjustmentsForInterestOnPensionAndOtherPostEmploymentBenefitObligations	15,800,000
Adjustments For Interest on Pension and Other Post Employment Benefit Obligations	astl_AdjustmentsForInterestOnPensionAndOtherPostEmploymentBenefitObligations	16,100,000
Adjustments For Other Income	astl_AdjustmentsForOtherIncome	76,200,000
Adjustments For Other Income	astl_AdjustmentsForOtherIncome	32,700,000
Adjustments For Accretion of Governmental Loans and Environmental Liabilities	astl_AdjustmentsForAccretionOfGovernmentalLoansAndEnvironmentalLiabilities	16,000,000
Adjustments For Accretion of Governmental Loans and Environmental Liabilities	astl_AdjustmentsForAccretionOfGovernmentalLoansAndEnvironmentalLiabilities	12,300,000
Adjustments For Changes in Fair Value of Warrant Liability	astl_AdjustmentsForChangesInFairValueOfWarrantLiability	41,500,000
Adjustments For Changes in Fair Value of Warrant Liability	astl_AdjustmentsForChangesInFairValueOfWarrantLiability	(4,000,000)
Adjustments For Changes in Fair Value of Earnout Liability	astl_AdjustmentsForChangesInFairValueOfEarnoutLiability	5,600,000
Adjustments For Changes in Fair Value of Earnout Liability	astl_AdjustmentsForChangesInFairValueOfEarnoutLiability	(2,400,000)
Decrease Increase In Fair Value Of Share Based Payment Compensation Liability	astl_DecreaseIncreaseInFairValueOfShareBasedPaymentCompensationLiability	(19,800,000)
Decrease Increase In Fair Value Of Share Based Payment Compensation Liability	astl_DecreaseIncreaseInFairValueOfShareBasedPaymentCompensationLiability	5,300,000
Payments for Share Based Payment Compensation And Earnout Units Settled	astl_PaymentsForShareBasedPaymentCompensationAndEarnoutUnitsSettled	0
Payments for Share Based Payment Compensation And Earnout Units Settled	astl_PaymentsForShareBasedPaymentCompensationAndEarnoutUnitsSettled	2,100,000
Payment of Environmental Liabilities Classified As Operating Activities	astl_PaymentOfEnvironmentalLiabilitiesClassifiedAsOperatingActivities	1,000,000
Payment of Environmental Liabilities Classified As Operating Activities	astl_PaymentOfEnvironmentalLiabilitiesClassifiedAsOperatingActivities	2,700,000
Proceeds Of Insurance For Operating Expenses	astl_ProceedsOfInsuranceForOperatingExpenses	53,500,000
Proceeds Of Insurance For Operating Expenses	astl_ProceedsOfInsuranceForOperatingExpenses	0
Insurance Proceeds For Property Damage	astl_InsuranceProceedsForPropertyDamage	15,000,000
Insurance Proceeds For Property Damage	astl_InsuranceProceedsForPropertyDamage	27,900,000
Proceeds From Sale of Land	astl_ProceedsFromSaleofLand	1,200,000
Proceeds From Sale of Land	astl_ProceedsFromSaleofLand	0
Bank Indebtedness Advanced Repaid Net Classified As Financing Activities	astl_BankIndebtednessAdvancedRepaidNetClassifiedAsFinancingActivities	171,400,000
Bank Indebtedness Advanced Repaid Net Classified As Financing Activities	astl_BankIndebtednessAdvancedRepaidNetClassifiedAsFinancingActivities	100,000
Restricted Cash Classified As Financing activity	astl_RestrictedCashClassifiedAsFinancingActivity	0
Restricted Cash Classified As Financing activity	astl_RestrictedCashClassifiedAsFinancingActivity	(3,800,000)
Senior Secured Lien Notes Issued, Net of Underwriter Fees	astl_SeniorSecuredLienNotesIssuedNetOfUnderwriterFees	0
Senior Secured Lien Notes Issued, Net of Underwriter Fees	astl_SeniorSecuredLienNotesIssuedNetOfUnderwriterFees	(472,600,000)
Transaction Costs on Senior Secured Lien Notes	astl_TransactionCostsOnSeniorSecuredLienNotes	0
Transaction Costs on Senior Secured Lien Notes	astl_TransactionCostsOnSeniorSecuredLienNotes	4,100,000
Proceeds From Governmental Loans	astl_ProceedsFromGovernmentalLoans	99,700,000
Proceeds From Governmental Loans	astl_ProceedsFromGovernmentalLoans	43,600,000
Governmental Loans Transaction Costs	astl_GovernmentalLoansTransactionCosts	2,800,000
Governmental Loans Transaction Costs	astl_GovernmentalLoansTransactionCosts	0
Government Grants In Respect Of Property Plant And Equipment Value	astl_GovernmentGrantsInRespectOfPropertyPlantAndEquipmentValue	34,800,000
Government Grants In Respect Of Property Plant And Equipment Value	astl_GovernmentGrantsInRespectOfPropertyPlantAndEquipmentValue	30,000,000
Government Grants In Respect Of Property Plant And Equipment Value	astl_GovernmentGrantsInRespectOfPropertyPlantAndEquipmentValue	35,100,000
Government Grants In Respect Of Property Plant And Equipment Value	astl_GovernmentGrantsInRespectOfPropertyPlantAndEquipmentValue	30,000,000
Government Grants In Service Of Property Plant And Equipment Value	astl_GovernmentGrantsInServiceOfPropertyPlantAndEquipmentValue	$ 123,500,000
Payments For Construction In Progress	astl_PaymentsForConstructionInProgress	$ 800,000
Payments For Construction In Progress	astl_PaymentsForConstructionInProgress	210,200,000
Maximum Funding Approved For Government Grant	astl_MaximumFundingApprovedForGovernmentGrant	$ 56,900,000
Increase Through Financing Cash Flows Liabilities Arising From Financing Activities	astl_IncreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities	$ 3,000,000
Increase Through Financing Cash Flows Liabilities Arising From Financing Activities	astl_IncreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities	213,900,000
Decrease Through Financing Cash Flows Liabilities Arising From Financing Activities	astl_DecreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities	(2,900,000)
Decrease Through Financing Cash Flows Liabilities Arising From Financing Activities	astl_DecreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities	$ (42,400,000)
Proportion Of Debt Instrument Issued	astl_ProportionOfDebtInstrumentIssued	9.125%
Borrowings interest payment basis	astl_BorrowingsInterestPaymentBasis	Interest payments are due April 15 and October 15, and commenced on October 15, 2024.
Underwriter Fees and Other Transaction Costs	astl_UnderwriterFeesAndOtherTransactionCosts	$ 10,100,000
Defined Contribution Plan Per Hour Contribution	astl_DefinedContributionPlanPerHourContribution	3.55
Defined Contribution Plan Per Hour Contribution	astl_DefinedContributionPlanPerHourContribution	3.85
Acturial Assumption Of Defined Benefit Costs Defined Obligation And Past Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsDefinedObligationAndPastServiceCostsPercentage	4.64%
Acturial Assumption Of Defined Benefit Costs Defined Obligation And Past Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsDefinedObligationAndPastServiceCostsPercentage	4.85%
Acturial Assumption Of Defined Benefit Costs Net Interest Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsNetInterestCostsPercentage	4.31%
Acturial Assumption Of Defined Benefit Costs Net Interest Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsNetInterestCostsPercentage	4.78%
Acturial Assumption Of Defined Benefit Costs Current Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsCurrentServiceCostsPercentage	4.75%
Acturial Assumption Of Defined Benefit Costs Current Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsCurrentServiceCostsPercentage	4.85%
Acturial Assumption Of Defined Benefit Costs Interest Costs On Current Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsInterestCostsOnCurrentServiceCostsPercentage	4.61%
Acturial Assumption Of Defined Benefit Costs Interest Costs On Current Service Costs Percentage	astl_ActurialAssumptionOfDefinedBenefitCostsInterestCostsOnCurrentServiceCostsPercentage	4.84%
Actual Return Net Of Investment Management Expenses	astl_ActualReturnNetOfInvestmentManagementExpenses	$ 61,400,000
Actual Return Net Of Investment Management Expenses	astl_ActualReturnNetOfInvestmentManagementExpenses	$ 105,800,000
Percentage Contributed To Fair Value Of Plan Assets	astl_PercentageContributedToFairValueOfPlanAssets	100.00%
Percentage Contributed To Fair Value Of Plan Assets	astl_PercentageContributedToFairValueOfPlanAssets	100.00%
Reasonably Possible Increase In Acturial Assumption By One Year	astl_ReasonablyPossibleIncreaseInActurialAssumptionByOneYear	1
Reasonably Possible Increase In Acturial Assumption By One Year	astl_ReasonablyPossibleIncreaseInActurialAssumptionByOneYear	1
Reasonably Possible Decrease In Acturial Assumption By One Year	astl_ReasonablyPossibleDecreaseInActurialAssumptionByOneYear	1
Reasonably Possible Decrease In Acturial Assumption By One Year	astl_ReasonablyPossibleDecreaseInActurialAssumptionByOneYear	1
Percentage deficit in the return on plan assets	astl_PercentageDeficitInTheReturnOnPlanAssets	10.00%
Percentage deficit in the return on plan assets	astl_PercentageDeficitInTheReturnOnPlanAssets	10.00%
Decrease In Other Comprehensive Income After Tax Due To Possible Percentage Deficit In The Return On Plan Assets	astl_DecreaseInOtherComprehensiveIncomeAfterTaxDueToPossiblePercentageDeficitInTheReturnOnPlanAssets	$ 110,000,000
Decrease In Other Comprehensive Income After Tax Due To Possible Percentage Deficit In The Return On Plan Assets	astl_DecreaseInOtherComprehensiveIncomeAfterTaxDueToPossiblePercentageDeficitInTheReturnOnPlanAssets	$ 105,000,000
NumberOfSharesIssuedDuringPeriod	astl_Numberofsharesissuedduringperiod	755,730
NumberOfSharesIssuedDuringPeriod	astl_Numberofsharesissuedduringperiod	75,000
NumberOfSharesIssuedDuringPeriod	astl_Numberofsharesissuedduringperiod	104,123,072
Common Shares Issued Upon Exercise Of Earnout Rights	astl_CommonSharesIssuedUponExerciseOfEarnoutRights	75,000
Common Shares Issued Upon Exercise Of Earnout Rights	astl_CommonSharesIssuedUponExerciseOfEarnoutRights	755,730
NumberOfSharesAuthorizedToBeRepurchased	astl_Numberofsharesauthorizedtoberepurchased	5,206,153
Number Of Other Equity Instruments Granted In ShareBased Payment Arrangement As Dividend Equivalents	astl_NumberOfOtherEquityInstrumentsGrantedInSharebasedPaymentArrangementAsDividendEquivalents	457,935
Number Of Other Equity Instruments Granted In ShareBased Payment Arrangement As Dividend Equivalents	astl_NumberOfOtherEquityInstrumentsGrantedInSharebasedPaymentArrangementAsDividendEquivalents	404,211
Number Of Share Options Granted In Share Based Payment Arrangement As Dividend Equivalents	astl_NumberOfShareOptionsGrantedInShareBasedPaymentArrangementAsDividendEquivalents	569,536
Number Of Share Options Granted In Share Based Payment Arrangement As Dividend Equivalents	astl_NumberOfShareOptionsGrantedInShareBasedPaymentArrangementAsDividendEquivalents	953,783
Number Of Share Options Granted In Share Based Payment Arrangement As Dividend Equivalents	astl_NumberOfShareOptionsGrantedInShareBasedPaymentArrangementAsDividendEquivalents	565,016
Number Of Share Options Granted In Share Based Payment Arrangement As Dividend Equivalents	astl_NumberOfShareOptionsGrantedInShareBasedPaymentArrangementAsDividendEquivalents	1,042,775
Dilutive Effect of Restricted Share Units and Performance Share Units	astl_DilutiveEffectOfRestrictedShareUnitsAndPerformanceShareUnits	467,301
Dilutive Effect of Restricted Share Units and Performance Share Units	astl_DilutiveEffectOfRestrictedShareUnitsAndPerformanceShareUnits	399,812
Weighted Average Common Shares Issued	astl_WeightedAverageCommonSharesIssued	104,924,898
Weighted Average Common Shares Issued	astl_WeightedAverageCommonSharesIssued	104,304,638
Weighted Average Common Shares Outstanding	astl_WeightedAverageCommonSharesOutstanding	104,924,898
Weighted Average Common Shares Outstanding	astl_WeightedAverageCommonSharesOutstanding	104,304,638
Weighted Average Common Shares Outstanding	astl_WeightedAverageCommonSharesOutstanding	662,296
Weighted Average Common Shares Outstanding	astl_WeightedAverageCommonSharesOutstanding	1,007,245
Accounts receivable overdue amount	astl_AccountsReceivableOverdueAmount	$ 9,300,000
Accounts receivable overdue amount	astl_AccountsReceivableOverdueAmount	$ 9,800,000
Percentage of accounts receivable overdue	astl_PercentageOfAccountsReceivableOverdue	5.40%
Percentage of accounts receivable overdue	astl_PercentageOfAccountsReceivableOverdue	4.30%
Accounts receivable overdue period.	astl_AccountsReceivableOverduePeriod.	90 days
Net Canadian Dollar Denominated Financial Instruments	astl_NetCanadianDollarDenominatedFinancialInstruments	$ (336,500,000)
Net Canadian Dollar Denominated Financial Instruments	astl_NetCanadianDollarDenominatedFinancialInstruments	$ (212,700,000)
Aggregate Notional Quantity Outstanding	astl_AggregateNotionalQuantityOutstanding	0
Aggregate Notional Quantity Outstanding	astl_AggregateNotionalQuantityOutstanding	0
Key management personnel ShareBased Compensation	astl_KeyManagementPersonnelSharebasedCompensation	$ (3,200,000)
Key management personnel ShareBased Compensation	astl_KeyManagementPersonnelSharebasedCompensation	5,800,000
Libor [Member]
Line Of Credit Maximum Borrowing Capacity	astl_LineOfCreditMaximumBorrowingCapacity	300,000,000
Line Of Credit Maximum Borrowing Capacity	astl_LineOfCreditMaximumBorrowingCapacity	$ 375,000,000
Letters Of Credit Outstanding And Borrowing Base Reserves	astl_LettersOfCreditOutstandingAndBorrowingBaseReserves	$ 66,100,000
Letters Of Credit Outstanding And Borrowing Base Reserves	astl_LettersOfCreditOutstandingAndBorrowingBaseReserves	$ 48,200,000
Letters Of Credit Outstanding And Borrowing Base Reserves	astl_LettersOfCreditOutstandingAndBorrowingBaseReserves	$ 69,500,000
Letters Of Credit Outstanding And Borrowing Base Reserves	astl_LettersOfCreditOutstandingAndBorrowingBaseReserves	$ 48,300,000
Renewed Normal Course Issuer Bid [Member]
Percentage of Warrants authorized to be repurchased as of shares issued	astl_PercentageofWarrantsauthorizedtoberepurchasedasofsharesissued	5.00%
MaximumNumberOfSharesToBeRepurchasedPerDay	astl_Maximumnumberofsharestoberepurchasedperday	12,066
Percentage Of Maximum Number of Shares To Be Repurchase Per Day	astl_PercentageOfMaximumNumberofSharesToBeRepurchasePerDay	25.00%
Average Number Of Daily Trading Volume Of Shares	astl_AverageNumberOfDailyTradingVolumeOfShares	48,264
Average Number Of Daily Trading Volume Of Shares	astl_AverageNumberOfDailyTradingVolumeOfShares	1,059
Number Of Warrants Authorized To Be Repurchased	astl_NumberOfWarrantsAuthorizedToBeRepurchased	1,208,950
Number Of Warrants Issued During Period	astl_NumberOfWarrantsIssuedDuringPeriod	24,179,000
Maximum Number Of Warrants To Be Repurchased Per Day	astl_MaximumNumberOfWarrantsToBeRepurchasedPerDay	1,000
Maximum Number Of Warrants To Be Repurchased Per Day	astl_MaximumNumberOfWarrantsToBeRepurchasedPerDay	1,000
Percentage Of Maximum Number Of Warrants To Be Repurchased Per Day	astl_PercentageOfMaximumNumberOfWarrantsToBeRepurchasedPerDay	25.00%
United States of America, Dollars
Possible decrease in the value of foreign currency againstthe local currency.	astl_PossibleDecreaseInTheValueOfForeignCurrencyAgainsttheLocalCurrency.	0.01
Accounts Receivable [Member]
Allowance account for credit losses of financial asset	astl_AllowanceAccountForCreditLossesOfFinancialAsset	$ 9,000,000
Allowance account for credit losses of financial asset	astl_AllowanceAccountForCreditLossesOfFinancialAsset	8,800,000
Other Non Current Assets [Member] \| Libor [Member]
Unamortized Debt Issuance Costs	astl_UnamortizedDebtIssuanceCosts	800,000
Unamortized Debt Issuance Costs	astl_UnamortizedDebtIssuanceCosts	$ 1,100,000

Earnout Liability (Tables)

12 Months Ended

Dec. 31, 2025

Earnout Liability [Abstract]

Summary of Continuity of Earnout Rights

Continuity of earnout rights are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

(in units)

Opening balance		719,547		1,196,157

Dividend equivalents and other adjustments		10,906		16,176

Vested and settled		(75,000)		(320,000)

Cancellations		-		(172,786)


Ending balance		655,453		719,547

Governmental Loans (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Details in Tabular Form of Governmental Loans


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Long-term portion

Federal AMF Loan, denominated in Canadian dollars, due March 1, 2028	$	20.2	$	16.6

Provincial MENDM Loan, denominated in Canadian dollars, due November 30, 2028		34.0		35.8

Federal SIF Agreement loan, denominated in Canadian dollars, due April 30, 2031		10.6		9.9

Federal SIF EAF Agreement loan, denominated in Canadian dollars, due January 1, 2030		83.1		71.3

Federal LETL loan, denominated in Canadian dollars, due November 14, 2032		35.5		-

Provincial LETL loan, denominated in Canadian dollars, due November 14, 2032		8.9		-


	$	192.3	$	133.6


Current portion

Federal AMF Loan, denominated in Canadian dollars	$	0.3	$	10.0

Provincial MENDM Loan, denominated in Canadian dollars		13.7		15.0


	$	14.0	$	25.0


	$	206.3	$	158.6

Summary of Company's Long-term Debt Facilities Arising From Financing Activities

The changes in the Company’s governmental loan facilities arising from financing activities are presented below:


	Governmental Loan Issued (Repaid) *			Governmental loan benefit recognized immediately			Accretion of governmental loan benefit		Carrying value

Federal AMF Loan

Balance at December 31, 2024	$	31.7		$	(26.5	)	$	21.2	$	26.6

Movement in the period		(5.2	)		(3.0	)		2.1		(6.1	)


Balance at December 31, 2025	$	26.5		$	(29.5	)	$	23.3	$	20.5


Provincial MENDM Loan

Balance at December 31, 2024	$	58.8		$	(26.4	)	$	18.5	$	50.8

Movement in the period		(8.7	)		3.1			2.5		(3.1	)


Balance at December 31, 2025	$	50.1		$	(23.3)		$	21.0	$	47.7


Federal SIF Loan

Balance at December 31, 2024	$	15.0		$	(9.2	)	$	4.1	$	9.9

Movement in the period		-			-			0.7		0.7


Balance at December 31, 2025	$	15.0		$	(9.2)		$	4.8	$	10.6


Federal SIF EAF Loan

Balance at December 31, 2024	$	183.7		$	(120.3	)	$	7.9	$	71.3

Movement in the period		16.3			(10.8	)		6.3		11.8


Balance at December 31, 2025	$	200.0		$	(131.1)		$	14.2	$	83.1


Federal LETL Loan

Balance at December 31, 2024	$	-		$	-		$	-	$	-

Movement in the period		66.2			(31.0	)		0.3		35.5


Balance at December 31, 2025	$	66.2		$	(31.0)		$	0.3	$	35.5


Provincial LETL Loan

Balance at December 31, 2024	$	-		$	-		$	-	$	-

Movement in the period		16.6			(7.8	)		0.1		8.9


Balance at December 31, 2025	$	16.6		$	(7.8)		$	0.1	$	8.9


Total, Governmental Loans

Balance at December 31, 2024	$	289.2		$	(182.4	)	$	51.7	$	158.6

Movement in the period		85.2			(49.5	)		12.0		47.7


Balance at December 31, 2025	$	374.4		$	(231.9)		$	63.7	$	206.3

* Net of transaction costs and interest paid-in-kind for the Federal LETL Loan and Provincial LETL Loan.

Income Tax Recovery (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information About Components of Income Tax Expense Explanatory

The components of income tax recovery for the year ended December 31, 2025 and the nine month period ended December 31, 2024 are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024
Income tax (recovery) expense recognized in net loss:

Current tax recovery	$	(209.0	)	$	(52.7	)
Deferred income tax (recovery) expense		(106.8	)		6.5


	$	(315.8	)	$	(46.2	)

Summary of Income taxes in the consolidated statements of net (loss) income

Income taxes in the consolidated statements of net loss for the year ended December 31, 2025 and the nine month period ended December 31, 2024 vary from amounts that would be computed by applying statutory income tax rates for the following reason:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Loss before income taxes	$	(1,300.7	)	$	(213.2	)


Income tax recovery based on the applicable tax rate of 25%	$	(325.2	)	$	(53.3	)

Add / (deduct):

Non-deductible post-employment benefits payments		3.0			2.6

Non-deductible pension contributions		(0.3	)		0.9

Non-deductible accretion of financial obligations		1.0			0.6

Unrealized foreign exchange		5.4			-

Change in unrecognized tax benefits		33.4			-

Adjustment in respect of prior years		(13.5	)		0.8

Changes in fair value of IPO Warrant liability		(11.9	)		1.0

Changes in fair value of earnout liability		(1.4	)		0.6

Changes in fair value of share-based payment liability		(4.8	)		1.3

Changes in fair value of derivatives		3.3			-

Other		(4.9	)		(0.7	)


Income tax recovery	$	(315.8	)	$	(46.2	)

Other Post-Employment Benefits (Tables)

12 Months Ended

Dec. 31, 2025

Statement [Line Items]

Disclosure In Tabular Form Of Acturial Assumptons For Pension Plans [Table Text Block]

The principal assumptions used for the purposes of the actuarial valuations were as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Assumptions for determination of defined benefit cost:

Discount rate

Defined benefit obligation		4.70%		4.85%

Current service cost		4.81%		4.84%

Interest cost on benefit obligation		4.39%		4.79%

Interest cost on current service cost		4.80%		4.85%

Health care cost immediate trend rate		4.83%		4.90%

Assumptions for determination of defined benefit obligation:

Effective discount rate		4.98%		4.70%

Health care cost immediate trend rate		4.76%		4.83%

Assumptions for determination of defined benefit cost and defined benefit obligation:

Health care cost ultimate trend rate		4.00%		4.00%

Year ultimate health care cost trend rate reached		2040		2040

Salary Increases per annum		2.00%		2.00%

Mortality		105%CPM 2014 Private Projection CPM-B		105%CPM 2014 Private Projection CPM-B

Disclosure of Detailed Information About Other Post Employment Benefits Recognized in Statements of Income Loss Explanatory

The components of amounts recognized in the consolidated statements of net loss in respect of the

other

post-employment benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in net loss were as follows:

Current service cost	$	3.3	$	2.4

Past service cost		(6.0)		-

Net interest cost		8.8		8.0


	$	6.1	$	10.4


Post employment benefit costs recognized in:

Cost of sales	$	(2.5)	$	2.1

Administrative and selling expenses		(0.2)		0.3

Interest on other post-employment benefit obligation		8.8		8.0


	$	6.1	$	10.4

Disclosure of Detailed Information About Other Post Employment Benefits Recognized in Statements of Other Comprehensive income Loss Explanatory

The amounts recognized in the consolidated statements of other comprehensive (loss) income in respect of these other post-employment benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in other comprehensive loss, were as follows:

Actuarial gain on accrued post employment benefit liability	$	(8.8)	$	(25.3)

Summary of Other Comprehensive Income (Loss) in the Consolidated Statements of Changes in Shareholder's Equity

Reconciliation of the amounts recognized in accumulated other comprehensive (loss) income in the consolidated statements of changes in shareholders’ equity were as follows:


	Actuarial (gain) loss immediately recognized			Tax effect		Actuarial (gain) loss immediately recognized, net of tax

Balance at March 31, 2024	$	(73.5	)	$	-	$	(73.5	)

Actuarial gain immediately recognized		(25.3	)		-		(25.3	)


Balance at December 31, 2024	$	(98.8	)	$	-	$	(98.8	)

Actuarial gain immediately recognized		(8.8	)		-		(8.8	)

Balance at December 31, 2025	$	(107.6	)	$	-	$	(107.6	)

Summary of Continuities of the Defined Benefit Plan Assets and Obligations

Continuities of the other post-employment benefit plan assets and obligations are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Movements in the present value of the post-employment benefit plan assets were as follows:

Fair value of plan assets at beginning of the period and year, respectively	$	-		$	-
Employer contributions		10.6			8.5
Benefits paid		(10.6	)		(8.5	)
Fair value of plan assets at December 31, 2025 and

December 31, 2024, respectively	$	-		$	-


Movements in the present value of the other post-employment benefit obligation were as follows:

Defined benefit obligation at the beginning of the period and year, resepectively	$	206.2		$	229.5
Current service cost		3.3			2.4
Interest cost		8.8			8.0
Past service cost		(6.0	)		-
Actuarial (gains) losses arising from financial assumptions		(5.3	)		3.9
Actuarial gains arising from demographic assumptions		(5.5	)		(33.2	)
Actuarial losses from experience adjustments		2.1			4.1
Benefits paid		(10.6	)		(8.5	)
Defined benefit obligation at December 31, 2025 and

December 31, 2024, respectively	$	193.0		$	206.2

Pension Benefits (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of principal assumptions used for the purposes of the actuarial valuations

The principal assumptions used for the purposes of the actuarial valuations were as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Assumptions for determination of defined benefit cost:

Discount rate

Defined benefit obligation		4.70%		4.85%

Current service cost		4.81%		4.84%

Interest cost on benefit obligation		4.39%		4.79%

Interest cost on current service cost		4.80%		4.85%

Health care cost immediate trend rate		4.83%		4.90%

Assumptions for determination of defined benefit obligation:

Effective discount rate		4.98%		4.70%

Health care cost immediate trend rate		4.76%		4.83%

Assumptions for determination of defined benefit cost and defined benefit obligation:

Health care cost ultimate trend rate		4.00%		4.00%

Year ultimate health care cost trend rate reached		2040		2040

Salary Increases per annum		2.00%		2.00%

Mortality		105%CPM 2014 Private Projection CPM-B		105%CPM 2014 Private Projection CPM-B

Summary of Continuities of the defined benefit plan assets and obligations

Continuities of the defined benefit plan assets and obligations are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Movements in the present value of the plan assets were as follows:

Fair value of plan assets at beginning of the period and year, respectively	$	1,126.4		$	1,064.9
Actual return (net of investment management expenses)		61.4			105.8
Administration expenses		(2.0	)		(1.3	)
Employer contributions		28.0			20.0
Benefits paid		(86.2	)		(63.0	)
Fair value of plan assets at December 31, 2025 and

December 31, 2024, respectively	$	1,127.6		$	1,126.4


Movements in the present value of the defined benefit obligation were as follows:

Defined benefit obligation at the beginning of the period and year, respectively	$	1,304.7		$	1,302.9
Current service cost		13.5			10.5
Interest cost		54.1			45.1
Past service cost		5.6			-
Actuarial (gains) losses arising from financial assumptions		(21.1	)		28.8
Effect of experience adjustments		10.0			(19.6	)
Benefits paid		(86.2	)		(63.0	)
Defined benefit obligation at December 31, 2025 and


December 31, 2024, respectively	$	1,280.6		$	1,304.7

Summary of Reconciliation of the amounts recognized in accumulated other comprehensive income (loss)

Reconciliation of the amounts recognized in accumulated other comprehensive (loss) income in the consolidated statements of changes in shareholders’ equity were as follows:


	Actuarial (gain) loss immediately recognized			Tax effect		Actuarial (gain) loss immediately recognized, net of tax

Balance at March 31, 2024	$	(73.5	)	$	-	$	(73.5	)

Actuarial gain immediately recognized		(25.3	)		-		(25.3	)


Balance at December 31, 2024	$	(98.8	)	$	-	$	(98.8	)

Actuarial gain immediately recognized		(8.8	)		-		(8.8	)

Balance at December 31, 2025	$	(107.6	)	$	-	$	(107.6	)

Summary of major categories of plan assets

The major categories of plan assets were as follows:


As at	December 31, 2025	December 31, 2024

Cash and cash equivalents	1%	2%
Equity instruments	51%	50%
Debt instruments	45%	46%
Other	3%	2%


	100%	100%

Share-Based Compensation - Summary Of Continuity Of Deferred Share Units (Detail) - shares	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025	Mar. 31, 2025
Disclosure Of Terms And Conditions Of Deferred Share based Payment Arrangement [Line Items]
Dividend equivalents and other adjustments	4,941	7,124	43,127

Taxes Payable and Accrued Taxes

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Taxes Payable and Accrued Taxes

20.	TAXES PAYABLE AND ACCRUED TAXES


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Payroll taxes payable	$	4.1	$	7.0

Sales taxes payable		1.6		1.8

Carbon tax accrual		27.0		32.8


	$	32.7	$	41.6

Accounts Payable and Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Accounts Payable and Accrued Liabilities


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Accounts payable	$	47.7	$	146.1

Accrued liabilities		109.5		121.1

Wages and accrued vacation payable		46.7		51.9


	$	203.9	$	319.1

Net Change In Non-Cash Operating Working Capital (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary Of Changes In Non Cash Operating Working Capital


	Year ended December 31, 2025			Nine months ended December 31, 2024

Accounts receivable	$	29.8		$	39.4

Taxes receivable		(128.3	)		(61.6	)

Taxes payable		(7.4	)		9.4

Inventories		294.9			(19.5	)

Prepaid expenses and other current assets		10.5			41.5

Accounts payable and accrued liabilities		(124.5	)		(15.1	)


	$	75.1		$	(5.9	)

Share Based Compensation (Tables)

9 Months Ended

12 Months Ended

Dec. 31, 2024

Dec. 31, 2025

Disclosure Of Share Based Compensation [Line Items]

Summary of Continuity of Deferred Share Units

Continuity of deferred share units are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024
(in units)
Opening balance		480,481		344,768
Granted		218,069		130,772
Dividend equivalents and other adjustments		7,124		4,941

Ending balance		705,674		480,481

Disclosure of significant unobservable inputs used in fair value measurement of assets explanatory

The Monte-Carlo simulation was performed on the grant date, September 4, 2024, and used the following to estimate the fair value of the PSUs:


Common share price			$13.81
20-day VWAP as at April 1, 2024			$10.72
Term (in years)			3.0
Common share expected volatility			41.03%
Expected risk-free interest rate			3.09%

Summary of Continuity RSUs

Continuity of RSUs are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024
(in units)
Opening balance		1,037,229			607,252
Granted		565,016			569,536
Dividend equivalents and other adjustments, net of cancellations		(406,844	)		(75,279	)
Vested and settled		-			(64,280	)

Ending balance		1,195,401			1,037,229

Summary of Continuity of PSUs

Continuity of PSUs are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024
(in units)
Opening balance		1,049,039			231,898
Granted		1,042,775			953,783
Dividend equivalents and other adjustments, net of cancellations		(921,434	)		(63,146	)
Vested and settled		-			(73,496	)

Ending balance		1,170,381			1,049,039

Current Year 2025 Plan [Member]

Disclosure Of Share Based Compensation [Line Items]

Disclosure of significant unobservable inputs used in fair value measurement of assets explanatory

The Monte-Carlo simulation was performed on the grant date, August 21, 2025, and used the following to estimate the fair value of the PSUs:


Common share price			$6.36
20-day VWAP as at January 1, 2025			$14.04
Term (in years)			3.0
Common share expected volatility			43.94%
Expected risk-free interest rate			2.62%

Accounts Receivable, Net (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Account Receivable Net Explanatory


As at,	December 31, 2025			December 31, 2024

The carrying amount of:

Trade accounts receivable	$	172.4		$	222.5

Allowance for doubtful accounts		(9.0	)		(8.8	)

Governmental loan claims receivable

Federal Ministry of Industry, Strategic Innovation Fund (“Federal SIF”) Agreement		20.0			6.7

Northern Industrial Electricity Rate program rebate receivable		2.6			2.6

Other accounts receivable		6.7			4.6


	$	192.7		$	227.6

Allowance for doubtful accounts


Balance at March 31, 2024	$	(3.1	)
Adjustment to expected credit loss		(5.7	)

Balance at December 31, 2024	$	(8.8	)
Adjustment to expected credit loss		(0.2	)

Balance at December 31, 2025	$	(9.0)

Other Post-Employment Benefits - Summary of Continuities of the Defined Benefit Plan Assets and Obligations (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Statement [Line Items]
Benefits paid	$ (8.5)	$ (10.6)

Environmental Liabilities - Additional Information (Detail) - CAD ($) $ in Millions	9 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Statement [Line Items]
Letters Of Credit	$ 14.5	$ 16.6
Environmental costs recognized ,discount rate	7.30%	6.70%
Environmental costs recognized ,captalized in period	20 years
Increase In Liability	$ 1.7	$ 1.2
The companys operation site [member]
Statement [Line Items]
Letters Of Credit	14.3	16.4
Northern ontario mine sites owned by old steelco inc [member]
Statement [Line Items]
Letters Of Credit	$ 0.2	$ 0.2

Cost of Sales (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information About Cost of Sales Explanatory


	Year ended December 31, 2025		Nine months ended December 31, 2024

Total cost of sales is comprised of:

Cost of steel revenue	$	2,318.2	$	1,789.4

Cost of steel tariffs		225.0		-

Cost of freight revenue		175.3		142.7

Cost of non-steel revenue		32.0		26.3


	$	2,750.5	$	1,958.4


Inventories recognized as cost of sales:	$	2,575.2	$	1,815.7


Net inventory write-downs as a result of net realizable value lower than cost included in cost of sales:	$	24.4	$	29.3

Environmental Liabilities (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Environmental Liabilities


As at,	December 31, 2025		December 31, 2024

The carrying amount of Environmental liabilities in respect of:

The Company’s Operation Site	$	34.8	$	33.3
Northern Ontario mine sites owned by Old Steelco Inc.		4.2		4.2


	$	39.0	$	37.5


Current portion	$	4.7	$	4.2
Long-term portion		34.3		33.3

	$	39.0	$	37.5

Summary of Reconciliation of Environmental Liabilities


	The Company’s Operation Site			Northern Ontario mine sites owned by Old Steelco Inc.			Total

Balance at March 31, 2024	$	33.8		$	4.5		$	38.3

Payments		(2.7	)		(0.5	)		(3.2	)

Accretion of discount		3.7			0.4			4.1

Revaluation for change in discount rate		(1.5	)		(0.2	)		(1.7	)


Balance at December 31, 2024	$	33.3		$	4.2		$	37.5

Payments		(2.0	)		(0.5	)		(2.5	)

Accretion of discount		2.5			0.3			2.8

Revaluation for change in discount rate		1.0			0.2			1.2


Balance at December 31, 2025	$	34.8		$	4.2		$	39.0

Environmental Liabilities - Summary of Environmental Liabilities (Detail) - CAD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Disclosure of Detailed Information About Environmental liabilities [Line Items]
Environmental Liabilities	$ 39.0	$ 37.5
Current portion	4.7	4.2
Long-term portion	34.3	33.3
The Companys Operation Site [Member]
Disclosure of Detailed Information About Environmental liabilities [Line Items]
Environmental Liabilities	34.8	33.3
Northern Ontario mine sites owned by Old Steelco Inc [Member]
Disclosure of Detailed Information About Environmental liabilities [Line Items]
Environmental Liabilities	$ 4.2	$ 4.2

Administrative and Selling Expenses - Summary of Detailed Information About Administrative and Selling Expenses (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Administrative and selling expense is comprised of:
Software licenses	$ 5.3	$ 6.8
Amortization of intangible assets and non-producing assets	0.4	0.8
Other administrative and selling	$ 9.9	$ 9.6

Other Income

12 Months Ended

Dec. 31, 2025

Other Income [Abstract]

Disclosure of other income explanatory [text block

33.	OTHER INCOME

During the year ended December 31, 2025, the Company recognized other income of $76.2 million (December 31, 2024 - $32.7 million) comprised of $75.0 million (December 31, 2024 - $32.1 million) for insurance proceeds, of which $6.5 million remains in accounts receivable, and $1.2 million (December 31, 2024 – nil) for the sale of land in the consolidated statements of net loss.

Share-Based Payment Compensation Liability (Tables)

12 Months Ended

Dec. 31, 2025

Shared Based Payment Compensation Liability [Abstract]

Summary Of Continuity of Replacement LTIP Units

Continuity of Replacement LTIP units are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

(in units)

Opening balance		2,474,422		2,776,868

Dividend equivalents and other adjustments		40,844		43,127

Vested and settled		-		(297,953)

Cancellations		-		(47,620)


Ending balance		2,515,266		2,474,422

Governmental Loans - Additional Information (Detail) $ in Millions, $ in Millions			9 Months Ended		12 Months Ended
	Mar. 29, 2019 CAD ($)	Nov. 30, 2018 CAD ($)	Dec. 31, 2024 CAD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2025 CAD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2025 USD ($)	Nov. 14, 2025	Dec. 31, 2024 USD ($)	Mar. 25, 2024 CAD ($)	Sep. 20, 2021 CAD ($)
Statement [Line Items]
Eligible interest free loan		$ 60.0	$ 60.0		$ 60.0
Borrowings maturity start date	Apr. 30, 2027	Dec. 31, 2024
Governmental loans			26.6		20.5
Non current portion of governmental loans			71.3		83.1			$ 10.6		$ 9.9
Aggregate loan and grant eligible amount	$ 30.0
Interest free loan amount	$ 15.0										$ 15.0
Additional eligible interest free loan								15.0		15.0
Additional income from government grants				$ 5.1		$ 4.4
Repayment of government loans			7.5		5.2	8.7	$ 1.2
Governmental loans current and non-current								47.7		50.8
Repayment Of Government Loans Classified As Financing Activities			7.5		5.2	8.7	$ 1.2
Percentage Of Debt Instrument Held									20.00%
Percentage Of Revolving Credit Facility									80.00%
Transaction Cost For Debt Borrowing						0.1
Debt Instrument Interest Paid In Kind						0.1
Carrying Value Of Debt Instrument Held								8.9
Transaction Cost Related to Debt Instruement						$ 2.8
Unamortized Transaction Costs			(9.4)		(7.2)			$ 2.3		$ 0.0
Algoma Steel Parent SCA [Member]
Statement [Line Items]
Eligible interest free loan			43.8		200.0
Non current portion of governmental loans			$ 71.3		$ 83.1
Aggregate loan and grant eligible amount												$ 200.0

Tax Receivable - Summary of Taxes Receivable (Detail) - CAD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Tax Receivable [Abstract]
Sales taxes receivable	$ 5.1	$ 27.7
Income taxes receivable	201.8	56.6
Total tax receivable	$ 206.9	$ 84.3

Taxes Payable and Accrued Taxes - Summary of Taxes Payable and Accrued Taxes (Detail) - CAD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Disclosure of Detailed Information About Taxes Payable and Accrued Taxes [Abstract]
Carbon tax accrual	$ 27.0	$ 32.8
Taxes Payable and Accrued Taxes Current	$ 32.7	$ 41.6

Interest On Pension And Other Post-Employment Benefit Obligations - Summary of Interest On Pension And Other Post Employment Benefit Obligations (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Interest on pension and other post employment benefit obligations [Abstract]
Interest on defined benefit pension obligation	$ 8.1	$ 7.0
Interest on other post-employment benefit obligation	$ 8.0	$ 8.8

Net Change In Non-Cash Operating Working Capital

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Net Change In Non-Cash Operating Working Capital

31.	NET CHANGE IN NON-CASH OPERATING WORKING CAPITAL


	Year ended December 31, 2025			Nine months ended December 31, 2024

Accounts receivable	$	29.8		$	39.4

Taxes receivable		(128.3	)		(61.6	)

Taxes payable		(7.4	)		9.4

Inventories		294.9			(19.5	)

Prepaid expenses and other current assets		10.5			41.5

Accounts payable and accrued liabilities		(124.5	)		(15.1	)


	$	75.1		$	(5.9	)

Cover Page	12 Months Ended
Cover Page	Dec. 31, 2025 shares
Document Information [Line Items]
Document Type	40-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2025
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--03-31
Entity Registrant Name	ALGOMA STEEL GROUP INC.
Entity Central Index Key	0001860805
Entity File Number	001-40924
Document Annual Report	true
Document Registration Statement	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Incorporation, State or Country Code	A1
Entity Address, Address Line One	105 West Street
Entity Address, State or Province	ON
Entity Address, City or Town	Sault Ste. Marie
Entity Address, Country	CA
Entity Address, Postal Zip Code	P6A 7B4
City Area Code	705
Local Phone Number	945-2351
Title of 12(b) Security	Warrants, each whole warrant exercisable forone Common Share at an exercise price ofUS$11.50 per share
Trading Symbol	ASTLW
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding	104,933,802
Auditor Name	Deloitte LLP
Auditor Firm ID	1208
Auditor Location	Toronto, Canada
ICFR Auditor Attestation Flag	true
Audited Annual Financial Statements	true
Annual Information Form	true
Document Financial Statement Error Correction [Flag]	false
Business Contact [Member]
Document Information [Line Items]
Contact Personnel Name	Algoma Steel USA Inc.
Entity Address, Address Line One	1209 Orange Street
Entity Address, State or Province	DE
Entity Address, City or Town	Wilmington
Entity Address, Postal Zip Code	19801
City Area Code	302
Local Phone Number	658-7581

Cost of Sales - Additional Information (Detail) $ in Millions, $ in Millions	9 Months Ended		12 Months Ended
	Dec. 31, 2024 CAD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2025 CAD ($)	Dec. 31, 2025 USD ($)	Jun. 04, 2025	Mar. 04, 2025
Disclosure of Detailed Information About Cost of Sales [Line Items]
Carbon tax recognized as expense	$ 31.0		$ 31.4
Tariff costs		$ 0.0		$ 225.0
Ad Valorem Tariff Rate					50.00%	25.00%

Earnout Liability

12 Months Ended

Dec. 31, 2025

Earnout Liability [Abstract]

Earnout Liability

35.	EARNOUT LIABILITY

As at December 31, 2025, 655,453 earnout rights remain outstanding with an estimated fair value of US $4.10 per unit based on the market price of the Company’s common shares, for which an earnout liability of $3.7 million (US $2.7 million) (December 31, 2024 - $10.1 million; US $7.0 million) was recognized in the consolidated statements of financial position. During the year ended December 31, 2025, 75,000 earnout rights were settled for common shares. During the nine month period ended December 31, 2024, 320,000 earnout rights were settled for common shares and 172,786 earnout rights were cancelled. Gain on change in the fair value of the earnout liability for the year ended December 31, 2025 of $5.6 million is presented in the consolidated statements of net loss. Loss on

change in the fair value of the earnout liability for the nine month period ended December 31, 2024 of $2.4 million is presented in the consolidated statements of net loss.

Continuity of earnout rights are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

(in units)

Opening balance		719,547		1,196,157

Dividend equivalents and other adjustments		10,906		16,176

Vested and settled		(75,000)		(320,000)

Cancellations		-		(172,786)


Ending balance		655,453		719,547

Dividends - Summary of Dividends (Detail)	9 Months Ended	12 Months Ended
Dividends - Summary of Dividends (Detail)	Dec. 31, 2024	Dec. 31, 2025
April 10, 2025
Disclosure of Detailed Information About Dividends [Line Items]
Dividends Record Date		March 21, 2025
Dividends Payment Date	April 10, 2025
May 30, 2025
Disclosure of Detailed Information About Dividends [Line Items]
Dividends Record Date		May 13, 2025
Dividends Payment Date	May 30, 2025

Finance Costs - Summary of Detailed Information About Finance Cost Explanatory (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Disclosure Of Detailed Information About Finance Cost Explanatory [Line Items]
Other interest expense	$ 7.9	$ 3.5
Revaluation of discount rate for environmental liabilities	0.3	1.2
Unwinding of issuance costs of debt facilities and accretion of governmental loan benefits and discounts on environmental liabilities	$ 13.4	$ 17.1

Revenue (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Internal Performance Measurement and Resource Allocation


	Year ended December 31, 2025		Nine months ended December 31, 2024

Total revenue is comprised of:

Sheet & Strip	$	1,311.8	$	1,346.7

Plate		565.8		324.1

Slab		0.8		1.3

Freight		175.3		142.7

Non-steel revenue		32.0		26.3


	$	2,085.7	$	1,841.1


The geographical distribution of total revenue is as follows:

Sales to customers in Canada	$	930.4	$	672.5

Sales to customers in the United States		1,132.2		1,148.7

Sales to customers in the rest of the world		23.1		19.9


	$	2,085.7	$	1,841.1

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information Financial Assets And Liabilities Classified And Measured

The Company’s financial assets and liabilities are classified and measured as follows:


As at,		December 31, 2025				December 31, 2024
	Category	Carrying Value		Fair Value		Carrying Value		Fair Value

Financial assets

Cash (1)	Financial assets at amortized cost	$	77.5	$	77.5	$	266.9	$	266.9

Restricted cash (1)	Financial assets at amortized cost	$	0.1	$	0.1	$	0.1	$	0.1

Accounts receivable (2)	Financial assets at amortized cost	$	192.7	$	192.7	$	227.6	$	227.6

Other assets:

Other assets (1)	Financial assets at amortized cost	$	3.3	$	3.3	$	10.7	$	4.7

Derivative asset (3)	Financial instruments at FVTP(L)	$	-	$	-	$	5.9	$	5.9

Financial liabilities

Bank indebtedness (1)	Financial liabilities at amortized cost	$	170.2	$	170.2	$	0.4	$	0.4

Accounts payable and accrued liabilities (1)	Financial liabilities at amortized cost	$	203.9	$	203.9	$	319.1	$	319.1

Current portion of governmental loans (1)	Financial liabilities at amortized cost	$	14.0	$	14.0	$	25.0	$	25.0

Current portion of financing arrangement (1)	Financial liabilities at amortized cost	$	2.2	$	2.2	$	1.0	$	1.0

Severance cost liability (1)	Financial liabilities at amortized cost	$	45.8	$	45.8	$	-	$	-

Long-term governmental loans (1)	Financial liabilities at amortized cost	$	192.3	$	192.3	$	133.6	$	133.6

Long-term portion of financing arrangement (1)	Financial liabilities at amortized cost	$	21.6	$	21.6	$	12.6	$	12.6

IPO Warrant liability (4)	Financial instruments at FVTP(L)	$	2.5	$	2.5	$	52.2	$	52.2

Earnout liability (4)	Financial instruments at FVTP(L)	$	3.7	$	3.7	$	10.1	$	10.1

Share-based payment compensation liability (4)	Financial instruments at FVTP(L)	$	14.1	$	14.1	$	34.5	$	34.5

LETL Warrant liability (3)	Financial instruments at FVTP(L)	$	7.5	$	7.5	$	-	$	-

Senior secured lien notes (1)	Financial liabilities at amortized cost	$	476.6	$	400.0	$	498.4	$	515.2

- Initial measurement at fair value and subsequent remeasurement at amortized cost.

- Initial measurement at transaction price and subsequent remeasurement at amortized cost.

- Level 2; Initial measurement at fair value and subsequent remeasurement at FVTOCI(L)

- Level 1; Initial measurement at fair value and subsequent remeasurement at FVTP(L)

Summary of Company's Contractually Agreed (Undiscounted) Cash Flows Payable Under Financial Liabilities

The following table discloses the Company’s contractually agreed (undiscounted) cash flows payable under financial liabilities, as at December 31, 2025:


	Carrying Amount		Contractual Cash Flows		Year 1		Year 2		Years 3 to 5		Greater than 5 Years

Revolving Credit Facility	$	170.2	$	(170.2)	$	(170.2)	$	-	$	-	$	-

Accounts payable and accrued liabilities		203.9		(203.9)		(203.9)		-		-		-

Governmental Loans		206.3		(374.9)		(14.1)		(17.7)		(50.7)		(292.4)

Interest on Provincial MENDM Loan		-		(9.7)		(1.9)		(2.7)		(5.1)		-

Financing arrangements		24.5		(24.5)		(2.9)		(3.1)		(18.5)		-

Senior Secured Lien Notes		476.6		(479.7)		-		-		(479.7)		-

Interest on Senior Secured Lien Notes		-		(153.3)		(43.8)		(43.8)		(65.7)		-


	$	1,081.5	$	(1,416.2)	$	(436.8)	$	(67.3)	$	(619.7)	$	(292.4)

Key Management Personnel (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Remuneration of the Company's Board of Directors and ELT

having authority and responsibility for planning, directing and controlling the activities of the Company and include the executive leadership team (ELT) and the Board of Directors.

Remuneration of the Company’s Board of Directors and ELT for the respective periods are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024
Salaries and benefits	$	9.2		$	7.0
Director fees		1.0			1.2
Share-based compensation (Note 38)		(3.2	)		5.8

	$	7.0		$	14.0

Share-Based Payment Compensation Liability

12 Months Ended

Dec. 31, 2025

Shared Based Payment Compensation Liability [Abstract]

Share-Based Payment Compensation Liability

36.	SHARE-BASED PAYMENT COMPENSATION LIABILITY

Replacement Long Term Incentive Plan (“LTIP”) Awards

As at December 31, 2025, 2,515,266 Replacement LTIP Awards remain outstanding with an estimated fair value of US $4.10 per unit based on the market price of the Company’s common shares, for which the Company recognized a liability of $14.1 million (US $10.3 million) (December 31, 2024 - $34.5 million; US $24.0 million) in share-based payment compensation liability in the consolidated statements of financial position. During the year ended December 31, 2025, no units were settled. During the nine month period ended December 31, 2024, 297,953 units were settled for common shares and 47,620 units were cancelled. A portion of the common shares issued to settle these units were sold by the Company for cash of $2.1 million used to settle withholding taxes. Gain on change in the fair value of the share-based payment compensation liability for the year ended December 31, 2025 of $19.8 million is presented in the consolidated statements of net loss. Loss on change in the fair value of the share-based payment compensation liability for the nine month period ended December 31, 2024 of $5.3 million presented in the consolidated statements of net loss.

Continuity of Replacement LTIP units are as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

(in units)

Opening balance		2,474,422		2,776,868

Dividend equivalents and other adjustments		40,844		43,127

Vested and settled		-		(297,953)

Cancellations		-		(47,620)


Ending balance		2,515,266		2,474,422

Property, Plant and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Changes in Cost of Property Plant and Equipment

The following table presents the changes to the cost of the Company’s property, plant and equipment for the year ended December 31, 2025 and the nine month period ended December 31, 2024:


Cost	Freehold Land			Buildings			Machinery & Equipment			Computer Hardware			Right-of- use assets			Property under construction			Total

Balance at March 31, 2024	$	6.7		$	91.0		$	1,181.0		$	5.6		$	7.7		$	638.3		$	1,930.3

Additions		-			-			11.5			-			-			258.9			270.4

Transfers		-			1.3			111.9			2.2			0.4			(115.7	)		0.1

Disposals		-			(0.1	)		(7.4	)		-			-			(1.6	)		(9.1	)

Foreign exchange		0.4			5.8			79.6			0.4			0.5			44.7			131.4


Balance at December 31, 2024	$	7.1		$	98.0		$	1,376.6		$	8.2		$	8.6		$	824.6		$	2,323.1

Additions		-			-			8.7			-			-			309.1			317.8

Transfers		-			466.5			390.4			2.4			-			(859.3	)		-

Disposals		-			(0.2	)		(7.2	)		-			-			-			(7.4	)

Foreign exchange		(0.4	)		(7.9	)		(71.6	)		(0.5	)		(0.4	)		(32.0	)		(112.8	)

Balance at December 31, 2025	$	6.7		$	556.4		$	1,696.9		$	10.1		$	8.2		$	242.4		$	2,520.7

Summary of Changes to Accumulated Depreciation of Property Plant and Equipment

The following table presents the changes to accumulated depreciation and impairment loss on the Company’s property, plant and equipment for the year ended December 31, 2025 and the nine month period ended December 31, 2024:


Accumulated Depreciation and Impairment Loss:	Freehold Land		Buildings			Machinery & Equipment			Computer Hardware			Right-of- use assets			Property under construc- tion			Total

Balance at March 31, 2024	$	-	$	38.6		$	483.4		$	1.6		$	1.5		$	-		$	525.1

Depreciation expense		-		3.3			100.7			0.7			0.6			-			105.3

Disposals		-		(0.1	)		(7.2	)		-			-			-			(7.3	)

Foreign exchange		-		2.6			34.5			0.1			0.1			-			37.3


Balance at December 31, 2024	$	-	$	44.4		$	611.4		$	2.4		$	2.2		$	-		$	660.4

Depreciation expense		-		8.8			366.0			1.1			0.8			-			376.7

Disposals		-		-			(7.0	)		-			-			-			(7.0	)

Foreign exchange		-		(3.3	)		(38.1	)		(0.1	)		(0.2	)		(0.9	)		(42.6	)

Impairment loss		2.0		145.0			289.5			2.0			1.6			63.2			503.3


Balance at December 31, 2025	$	2.0	$	194.9		$	1,221.8		$	5.4		$	4.4		$	62.3		$	1,490.8

Governmental Loans

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Governmental Loans

22.	GOVERNMENTAL LOANS


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Long-term portion

Federal AMF Loan, denominated in Canadian dollars, due March 1, 2028	$	20.2	$	16.6

Provincial MENDM Loan, denominated in Canadian dollars, due November 30, 2028		34.0		35.8

Federal SIF Agreement loan, denominated in Canadian dollars, due April 30, 2031		10.6		9.9

Federal SIF EAF Agreement loan, denominated in Canadian dollars, due January 1, 2030		83.1		71.3

Federal LETL loan, denominated in Canadian dollars, due November 14, 2032		35.5		-

Provincial LETL loan, denominated in Canadian dollars, due November 14, 2032		8.9		-


	$	192.3	$	133.6


Current portion

Federal AMF Loan, denominated in Canadian dollars	$	0.3	$	10.0

Provincial MENDM Loan, denominated in Canadian dollars		13.7		15.0


	$	14.0	$	25.0


	$	206.3	$	158.6

Federal Economic Development Agency for Southern Ontario

On November 30, 2018, the Company entered into an agreement with the Federal Economic Development Agency, through the Advanced Manufacturing Fund (“Federal AMF Loan”). The Company received a $60.0 million interest free loan as reimbursement for certain defined capital expenditures. The Company commenced equal monthly installments on April 1, 2022 to July 1, 2025 under the terms of the original agreement. On July 17, 2025, the Company amended the Federal AMF Loan agreement and will repay in amended monthly installments until March 1, 2031. Under the General Security Agreement, this facility has a third priority claim on all of the Company’s assets which is

pari passu

with the Provincial MENDM Loan, defined below.

As at December 31, 2025, the Company had applied for reimbursements of $60.0 million and recognized a benefit, net of accretion, of $6.2 million. During the year ended December 31, 2025, the Company made repayments totalling $5.2 million. Accordingly, the carrying value of the Federal AMF Loan was $20.5 million at December 31, 2025. As at December 31, 2024, the Company had applied for reimbursements of $60.0 million and recognized a benefit, net of accretion, of $5.3 million. During the nine month period ended December 31, 2024, the Company made repayments totalling $7.5 million. Accordingly, the carrying value of the Federal AMF Loan was $26.6 million at December 31, 2024.

Ministry of Energy, Northern Development and Mines

On November 30, 2018, the Company entered into an agreement with the Ministry of Energy, Northern Development and Mines (the “Provincial MENDM Loan”) under which, the Company received a $60.0 million low interest loan as reimbursement for certain defined capital expenditures.

Per the original agreement, the Company was required to repay the loan in monthly blended payments of principal and interest beginning on December 31, 2024 and ending on November 30, 2028. On August 21, 2025, the Company amended the Provincial MENDM Loan agreement and will defer payments commencing August 1, 2025 through to January 31, 2026. This facility matures May 31, 2029 and bears interest at an annual interest rate equal to the greater of 2.5% per annum; and the lenders cost of funds. Under the General Security Agreement, this facility has a third priority claim on all of the Company’s assets which is

pari passu

with the Federal AMF Loan.

As at December 31, 2025, the Company had applied for and received reimbursements of $60.0 million and recognized a benefit, net of accretion, of $2.3 million. During the year ended December 31, 2025, the Company made repayments totalling $8.7 million. Accordingly, the carrying value of the Provincial MENDM Loan was $47.7 million at December 31, 2025. As at December 31, 2024, the Company had applied for and received reimbursements of $60.0 million and recognized a benefit, net of accretion, of $7.9 million. During the year ended December 31, 2024, the Company made repayments totalling $1.2 million. Accordingly, the carrying value of the Provincial MENDM Loan was $50.8 million at December 31, 2024.

Ministry of Industry

On March 29, 2019, the Company, together with the government of Canada, entered into an agreement whereby a benefit of $30.0 million flowed to the Company; $15.0 million in the form of a grant, and $15.0 million in the form of an interest free loan; from the Ministry of Industry, Strategic Innovation Fund (the “SIF Agreement”). Under the terms of this agreement, the Company was reimbursed for certain defined capital. On March 25, 2024, the Company amended the SIF Agreement and will repay in equal annual instalments, the $15.0 million interest free loan portion of this funding beginning on April 30, 2027 and ending on April 30, 2034. The agreement is guaranteed by the Company’s subsidiary, Algoma Steel Intermediate Holdings Inc.

At December 31, 2025, the Company had applied for reimbursements of $15.0 million each under the grant and loan portions of the agreement, and recognized a benefit of $15.0 million. Additionally, at December 31, 2025, the Company had recognized a benefit, net of accretion, of $4.4 million. The carrying value of the Federal SIF Agreement was $10.6 million at December 31, 2025. At December 31, 2024, the Company had applied for reimbursements of $15.0 million each under the grant and loan portions of the agreement, and recognized a benefit of $15.0 million. Additionally, at December 31, 2024, the Company had recognized a benefit, net of accretion, of $5.1 million. The carrying value of the Federal SIF Agreement was $9.9 million at December 31, 2024.

On September 20, 2021, the Company, together with the government of Canada, entered into an agreement of which a benefit of up to $200.0 million would flow to the Company in the form of a loan from the SIF. Under the terms of the SIF agreement, the Company will be reimbursed for certain defined capital expenditures incurred to transition from blast furnace steel production to EAF steel production between March 3, 2021 and March 31, 2025. The repayment period will commence upon the earlier of the Company having access to full power from the provincial electricity grid to operate the EAF independently, or January 1, 2030. The annual repayment is further dependent on the Company’s performance in reducing its GHG emissions.

At December 31, 2025, the Company had applied for reimbursement of $200.0 million and recognized a benefit, net of accretion, in respect of this agreement of $116.9 million. Accordingly, the carrying value of the SIF EAF Agreement was $83.1 million. For the nine month period ended December 31, 2024, the Company had applied for reimbursements under the SIF loan agreement of $43.8 million and recognized a benefit, net of

accretion, in respect of this agreement of $26.0 million. Accordingly, the carrying value of the SIF EAF Agreement was $71.3 million.

Canada Enterprise Emergency Funding Corporation and Ministry of Northern Economic Development and Growth

On November 14, 2025, the Company entered into agreements with Canada Enterprise Emergency Funding Corporation under the Large Enterprise Tariff Loan (the “Federal LETL”) program and the Ministry of Northern Economic Development and Growth (the “Provincial LETL”) to secure a $500 million governmental loan comprised of a $400 million loan facility from the government of Canada and a $100 million loan facility from the Province of Ontario (collectively, the “Facilities”). The Facilities will be provided proportionately for which 20% shall be secured, ranking junior to the Company’s existing first lien Revolving Credit Facility and the Notes, with the remaining 80% of the Facilities being unsecured. The Facilities include customary positive and negative covenants, including a restriction on capital distributions.

The Facilities are subject to the issuance of 6.77

million common share purchase LETL Warrants to Canada Enterprise Emergency Funding Corporation (5.42 million LETL Warrants) and His Majesty the King in Right of Ontario (

1.35

million LETL Warrants), with each LETL Warrant being exercisable for one common share of the Company at an exercise price of $

11.08

for a

ten-year

term, vesting proportionately as unsecured draws are made. The Facilities have a seven-year term, with interest at CORRA + 200 bps for three years, stepping up by 200 bps each year thereafter. The exercise price of the LETL Warrants is equivalent to the volume-weighted average trading price of the Company’s common shares on the TSX from the completion of its going-public transaction in October 2021 through November 1, 2024, which was prior to the Section 232 tariffs imposed by the U.S. The LETL Warrants represent an embedded derivative for which a derivative liability has been presented on the consolidated statements of financial position totalling $

7.5

million and a corresponding loss has been included in change in fair value of IPO and LETL Warrant liabilities in the consolidated statements of net loss. As at December 31, 2025, no LETL warrants have vested.

For the year ended December 31, 2025, the Company received $66.2 million and $16.6 million loan proceeds, net of transaction costs of $0.4 million and $0.1 million, and interest paid in kind totalling $0.2 million and $0.1 million, for the Federal LETL and Provincial LETL, respectively. The Company recognized a benefit, net of accretion, in respect of these agreements of $30.7 million and $7.7 million for the Federal LETL and Provincial LETL, respectively. Accordingly, the carrying value of the Federal LETL agreement and Provincial LETL agreement was $35.5 million and $8.9 million, respectively.

Transaction costs related to the Facilities amounted to $2.8 million. Transaction costs are presented as other long-term assets in the consolidated statements of financial position. Transaction costs are allocated proportionately based on the amount drawn down on the Facilities. At December 31, 2025, the unamortized transaction costs related to the Facilities were $2.3 million (December 31, 2024 - nil).

The Company has recognized the governmental loan claims receivable, governmental loan payable and benefit associated with these agreements because the Company has fulfilled its obligations under the respective agreements and has reasonable assurance the grant will be received.

The changes in the Company’s governmental loan facilities arising from financing activities are presented below:


	Governmental Loan Issued (Repaid) *			Governmental loan benefit recognized immediately			Accretion of governmental loan benefit		Carrying value

Federal AMF Loan

Balance at December 31, 2024	$	31.7		$	(26.5	)	$	21.2	$	26.6

Movement in the period		(5.2	)		(3.0	)		2.1		(6.1	)


Balance at December 31, 2025	$	26.5		$	(29.5	)	$	23.3	$	20.5


Provincial MENDM Loan

Balance at December 31, 2024	$	58.8		$	(26.4	)	$	18.5	$	50.8

Movement in the period		(8.7	)		3.1			2.5		(3.1	)


Balance at December 31, 2025	$	50.1		$	(23.3)		$	21.0	$	47.7


Federal SIF Loan

Balance at December 31, 2024	$	15.0		$	(9.2	)	$	4.1	$	9.9

Movement in the period		-			-			0.7		0.7


Balance at December 31, 2025	$	15.0		$	(9.2)		$	4.8	$	10.6


Federal SIF EAF Loan

Balance at December 31, 2024	$	183.7		$	(120.3	)	$	7.9	$	71.3

Movement in the period		16.3			(10.8	)		6.3		11.8


Balance at December 31, 2025	$	200.0		$	(131.1)		$	14.2	$	83.1


Federal LETL Loan

Balance at December 31, 2024	$	-		$	-		$	-	$	-

Movement in the period		66.2			(31.0	)		0.3		35.5


Balance at December 31, 2025	$	66.2		$	(31.0)		$	0.3	$	35.5


Provincial LETL Loan

Balance at December 31, 2024	$	-		$	-		$	-	$	-

Movement in the period		16.6			(7.8	)		0.1		8.9


Balance at December 31, 2025	$	16.6		$	(7.8)		$	0.1	$	8.9


Total, Governmental Loans

Balance at December 31, 2024	$	289.2		$	(182.4	)	$	51.7	$	158.6

Movement in the period		85.2			(49.5	)		12.0		47.7


Balance at December 31, 2025	$	374.4		$	(231.9)		$	63.7	$	206.3

* Net of transaction costs and interest paid-in-kind for the Federal LETL Loan and Provincial LETL Loan.

Environmental Liabilities - Summary of Reconciliation of Environmental Liabilities (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Disclosure of Detailed Information About Reconciliation of Environmental Liabilities Explanatory [Line Items]
Accretion of discount	$ 4.1	$ 2.8
Revaluation for change in discount rate	(1.7)	1.2
The Companys Operation Site [Member]
Disclosure of Detailed Information About Reconciliation of Environmental Liabilities Explanatory [Line Items]
Accretion of discount	3.7	2.5
Revaluation for change in discount rate	(1.5)	1.0
Northern Ontario mine sites owned by Old Steelco Inc [Member]
Disclosure of Detailed Information About Reconciliation of Environmental Liabilities Explanatory [Line Items]
Accretion of discount	0.4	0.3
Revaluation for change in discount rate	$ (0.2)	$ 0.2

Severance Costs - Additional Information (Detail) $ in Millions, $ in Millions	Dec. 31, 2025 CAD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 CAD ($)
Severance Costs [Line Items]
Current Severance Cost Liability	$ 45.8	$ 45.8	$ 0.0

Income Tax (Recovery) Expense - Summary of Income taxes in the consolidated statements of net (loss) income (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Disclosure Of Reconciliation Of Tax Expense Income At Applicable Tax Rate To Provision For Income Taxes [Abstract]
Non-deductible pension contributions	$ 0.9	$ (0.3)
Non-deductible accretion of financial obligations	0.6	1.0
Unrealized foreign exchange		5.4
Change in unrecognized tax benefits		33.4
Adjustment in respect of prior years	0.8	(13.5)
Changes in fair value of IPO Warrant liability	1.0	(11.9)
Changes in fair value of earnout liability	0.6	(1.4)
Changes in fair value of share-based payment liability	1.3	(4.8)
Changes in fair value of derivatives		3.3
Income tax (recovery) expense	$ (46.2)	$ (315.8)

Accounts Receivable, Net - Summary of Account Receivable Net Explanatory (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Trade and Other Receivables [Line Items]
Allowance for doubtful accounts	$ (8.8)	$ (9.0)
Opening balance	(3.1)	(8.8)
Adjustment to expected credit loss	(5.7)	(0.2)
Ending balance	(8.8)	(9.0)
Federal Ministry of Industry, Strategic Innovation Fund ("Federal SIF") Agreement [member]
Trade and Other Receivables [Line Items]
Governmental loan claims receivable	6.7	20.0
Northern Industrial Electricity Rate program rebate receivable [member]
Trade and Other Receivables [Line Items]
Governmental loan claims receivable	$ 2.6	$ 2.6

Property, Plant and Equipment, Net - Summary of Changes to Accumulated Depreciation of Property Plant and Equipment (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Disclosure Of Detailed Information About Changes To Accumulated Amortisation Of Property Plant And Equipment [Line Items]
Disposals	$ (7.3)	$ (7.0)

General Information

12 Months Ended

Dec. 31, 2025

Statement [Line Items]

General Information

1.	GENERAL INFORMATION

Algoma Steel Group Inc., formerly known as 1295908 B.C. Ltd. (the “Company”), was incorporated on March 23, 2021 under the Business Corporations Act of British Columbia solely for the purpose of purchasing Algoma Steel Holdings Inc. The Company’s publicly traded securities under the symbol ‘ASTL’ and ASTLW’ are listed on the Toronto Stock Exchange (TSX) and the Nasdaq Stock Market (Nasdaq). Algoma Steel Group Inc. is the ultimate parent holding company of Algoma Steel Inc. and does not conduct any business operations.

Algoma Steel Inc. (“ASI”), the operating company and a wholly-owned subsidiary of Algoma Steel Holdings Inc. was incorporated on May 19, 2016 under the Business Corporations Act of British Columbia. ASI is a producer of hot and cold rolled steel products with its active operations located entirely in Sault Ste. Marie, Ontario, Canada. ASI produces sheet and plate products that are sold primarily in Canada and the United States.

The registered address of the Company is 1055 West Hastings Street, Vancouver, British Columbia, Canada. The head office of the Company is located at 105 West Street, Sault Ste. Marie, Ontario, Canada.

The consolidated financial statements of the Company as at December 31, 2025 and December 31, 2024 and for the year ended December 31, 2025 and nine month period ended December 31, 2024 are comprised of the Company and its wholly-owned subsidiaries as follows:

●

Algoma Steel Holdings Inc.

●

Algoma Steel Intermediate Holdings Inc.

●

Algoma Steel Inc.

●

Algoma Steel Inc. USA

●

Algoma Docks GP Inc.

●

Algoma Docks Limited Partnership

Algoma Steel Holdings Inc., Algoma Steel Intermediate Holdings Inc. and Algoma Docks GP Inc. are holding companies and do not conduct any business operations.

Governmental Loans - Summary of Details in Tabular Form of Governmental Loans (Detail) $ in Millions, $ in Millions	Dec. 31, 2025 CAD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 CAD ($)	Dec. 31, 2024 USD ($)
Disclosure Details Of Governmental Loans [Line Items]
Long-term governmental loans	$ 83.1	$ 10.6	$ 71.3	$ 9.9
Current portion of governmental loans	13.7		15.0
Governmental loans current and non current	$ 206.3		$ 158.6

Net Change In Non-Cash Operating Working Capital - Summary Of Changes In Non Cash Operating Working Capital (Detail) - Non Cash Item [Member] - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Schedule Of Changes In Non Cash Operating Working Capital [Line Items]
Taxes receivable	$ (61.6)	$ (128.3)
Taxes payable	9.4	(7.4)
Prepaid expenses and other current assets	$ 41.5	$ 10.5

Change of Fiscal Year-End

12 Months Ended

Dec. 31, 2025

Change of Fiscal Year End [Abstract]

Change of Fiscal Year-End

3.	CHANGE OF FISCAL YEAR-END

Effective November 5, 2024, the Board approved a change in the Company’s fiscal

year-end

from March 31 to December 31, effective as of December 31, 2024. The change in fiscal

year-end

from March 31 to December 31 was made to align the Company’s financial statement and continuous disclosure requirements with the majority of its industry peers, which operate on a calendar fiscal

year-end.

As a result, these consolidated financial statements include comparative financial information for the nine-month transition period from April 1, 2024, to December 31, 2024. The current year consolidated financial statements are for the twelve-month period from January 1, 2025, to December 31, 2025.

Environmental Liabilities

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Environmental Liabilites

26.	ENVIRONMENTAL LIABILITIES


As at,	December 31, 2025		December 31, 2024

The carrying amount of Environmental liabilities in respect of:

The Company’s Operation Site	$	34.8	$	33.3
Northern Ontario mine sites owned by Old Steelco Inc.		4.2		4.2


	$	39.0	$	37.5


Current portion	$	4.7	$	4.2
Long-term portion		34.3		33.3

	$	39.0	$	37.5

On November 30, 2018, the Company entered into agreements with the Province of Ontario, through the Ministry of the Environment, Conservation and Parks and the Ministry of Energy, Northern Development and Mines. These agreements relate to the Company’s operation site, and certain Northern Ontario mine sites owned by Old Steelco Inc., and not purchased by the Company. These agreements limit the Company’s obligations with respect to legacy environmental contamination, and impose certain risk management, risk mitigation, site remediation and funding obligations on the Company. The Company recognizes the present value of these environmental liabilities over 20 years commencing November 2018. Based on management’s review of the discount rate, at December 31, 2025, the discount rate was changed from 7.3% to 6.7% resulting in an increase in environmental liability of $1.2 million. Based on management’s review of the discount rate, at December 31, 2024, the discount rate was changed from 7.4% to 7.3% resulting in a decrease in environmental liability of $1.7 million.

At December 31, 2025, the Company has provided letters of credit totalling of $16.6 million (December 31, 2024 - $14.5 million) to the Ministry of Energy, Northern Development and Mines; $16.4 million in respect of the Company’s operation site (December 31, 2024 - $14.3 million) and $0.2 million (December 31, 2024 - $0.2 million) in respect of certain Northern Ontario mine sites owned by Old Steelco Inc. Letters of credit are disclosed in Note 13 and Note 18.

Reconciliation of Environmental liabilities


	The Company’s Operation Site			Northern Ontario mine sites owned by Old Steelco Inc.			Total

Balance at March 31, 2024	$	33.8		$	4.5		$	38.3

Payments		(2.7	)		(0.5	)		(3.2	)

Accretion of discount		3.7			0.4			4.1

Revaluation for change in discount rate		(1.5	)		(0.2	)		(1.7	)


Balance at December 31, 2024	$	33.3		$	4.2		$	37.5

Payments		(2.0	)		(0.5	)		(2.5	)

Accretion of discount		2.5			0.3			2.8

Revaluation for change in discount rate		1.0			0.2			1.2


Balance at December 31, 2025	$	34.8		$	4.2		$	39.0

Earnout Liability - Summary Of Continuity Of Earnout Rights (Detail) - shares	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Earnout Liability [Line Items]
Opening balance	1,196,157	719,547
Dividend equivalents and other adjustments	16,176	10,906
Vested and settled	(320,000)	(75,000)
Cancellations	(172,786)	0
Ending balance	719,547	655,453

Share-Based Compensation - Summary Of Continuity RSUs (Detail) - shares	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Financial Year 2025 Plan [Member]
Disclosure Of Terms And Conditions Of Restricted Share based Payment Arrangement [Line Items]
Dividend equivalents and other adjustments, net of cancellations	(63,146)	(921,434)

Pension Benefits

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Pension Benefits

23.	PENSION BENEFITS

Defined contribution plan

The Company maintains a defined contribution pension plan established by Old Steelco Inc.’s predecessor in 2004 for

non-unionized

employees in Canada joining the Company after January 1, 2003. As part of Old Steelco Inc.’s contract negotiations with its locals which concluded on July 31, 2010, the locals and Old Steelco Inc. agreed to include in this plan all unionized employees hired subsequent to August 1, 2010 and to offer to all the current employees the option to move to the Defined Contribution Pension Plan. Under the plan, the Company is obligated to provide a base contribution of 6% of salary and also match employee contributions to a maximum of 3%, depending on years of service for

non-unionized

employees. Additionally, the Company is obligated to provide a contribution for unionized employees per qualified hour worked of $3.55 to August 1, 2025 and increasing to $3.85 thereafter.

The pension expense under this plan is equal to the Company’s contribution. The pension expense for the year ended December 31, 2025 was $14.2 million. The pension expense for the nine month period ended December 31, 2024 was $10.9 million.

Defined benefit plans

The Company maintains

non-contributory

defined benefit pension plans that are closed to new entrants and cover all employees in Canada not covered under the Defined Contribution Pension Plan. The benefits are based on years of service and average earnings for a defined period prior to retirement.

The Company also maintains a closed plan for pensioners who retired prior to January 1, 2002, that provides the pensioners with a pension benefit in excess of the limits provided by the Ontario Pension Benefit Guarantee Fund (the “Closed Retiree Plan”).

These defined benefit pension plans are registered under the Pension Benefits Act (Ontario), and are legally separated from the Company. The Pension Benefits Act (Ontario) is a regulatory framework that has jurisdiction over the administration and funding of defined benefit pension plans. Within this framework, the Company has fiduciary responsibility over the administration of the defined benefit pension plans, including the development and oversight of the investment policy for pension funds and the selection and oversight of pension fund investment managers.

The defined benefit pension plans expose the Company to various risks such as: investment risk, interest rate risk, foreign currency risk, price risk, credit risk and liquidity risk.

The most recent actuarial valuations of plan assets and the present value of the defined benefit obligation were carried out at April 1, 2025 for salaried, hourly and wrap plans.

The principal assumptions used for the purposes of the actuarial valuations were as follows:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Assumptions for determination of defined benefit cost:

Defined obligation and past service cost		4.64%		4.85%

Net interest cost		4.31%		4.78%

Current service cost		4.75%		4.85%

Interest cost on current service cost		4.61%		4.84%

Discount rate for determination of defined benefit obligation		4.84%		4.64%

Assumptions for determination of defined benefit cost and defined benefit obligation:
		3.00% per		3.00% per
Ultimate rate of compensation		annum until		annum until
increase		2027		2027
		2.00%		2.00%
		thereafter		thereafter

		105%		105%
		CPM2014		CPM2014
Mortality		Private		Private
		Projection		Projection
		CPM-B		CPM-B

The components of amounts recognized in the consolidated statements of net loss in respect of the defined benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in net loss were as follows:

Current service cost	$	15.6	$	11.7

Past service cost		5.6		-

Net interest cost		7.0		8.1


	$	28.2	$	19.8


Defined benefit costs recognized in:

Cost of sales	$	19.1	$	10.5

Administrative and selling expenses		2.1		1.2

Interest on pension liability		7.0		8.1


	$	28.2	$	19.8

Past service cost recognition

On December 1, 2025 the Company issued 1,005 layoff notices to unionized employees which caused a curtailment and resulted in a past service cost adjustment related to the defined pension benefit plan of $5.6 million, of which $5.0 million was recorded in cost of steel revenue and $0.6 million was recorded in administrative and selling expense for the year ended December 31, 2025 (nil for the nine month period ended December 31, 2024).

The amounts recognized in the consolidated statements of other comprehensive (loss) income in respect of the defined benefit plans are presented below:


	Year ended December 31, 2025		Nine months ended December 31, 2024

Amounts recognized in other comprehensive loss, were as follows:

Actuarial gain on accrued pension liability	$	(25.5)	$	(59.5)

The amounts included in the consolidated statements of financial position in respect of the Company’s net obligation in respect of its defined benefit plans are as follows:


As at,	December 31, 2025		December 31, 2024

Present value of defined benefit obligation	$	1,280.6	$	1,304.7
Fair value of plan assets		1,127.6		1,126.4


Net accrued pension liability	$	153.0	$	178.3

Continuities of the defined benefit plan assets and obligations are as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Movements in the present value of the plan assets were as follows:

Fair value of plan assets at beginning of the period and year, respectively	$	1,126.4		$	1,064.9
Actual return (net of investment management expenses)		61.4			105.8
Administration expenses		(2.0	)		(1.3	)
Employer contributions		28.0			20.0
Benefits paid		(86.2	)		(63.0	)
Fair value of plan assets at December 31, 2025 and

December 31, 2024, respectively	$	1,127.6		$	1,126.4


Movements in the present value of the defined benefit obligation were as follows:

Defined benefit obligation at the beginning of the period and year, respectively	$	1,304.7		$	1,302.9
Current service cost		13.5			10.5
Interest cost		54.1			45.1
Past service cost		5.6			-
Actuarial (gains) losses arising from financial assumptions		(21.1	)		28.8
Effect of experience adjustments		10.0			(19.6	)
Benefits paid		(86.2	)		(63.0	)
Defined benefit obligation at December 31, 2025 and


December 31, 2024, respectively	$	1,280.6		$	1,304.7

Reconciliation of the amounts recognized in accumulated other comprehensive (loss) income in the consolidated statements of changes in shareholders’ equity were as follows:


	Actuarial (gain) loss immediately recognized			Tax effect			Actuarial (gain) immediately recognized, net of tax

Balance at March 31, 2024	$	(83.5	)	$	(0.3	)	$	(83.8	)

Actuarial gain immediately recognized		(59.5	)		-			(59.5	)


Balance at December 31, 2024	$	(143.0	)	$	(0.3	)	$	(143.3	)

Actuarial gain immediately recognized		(25.5	)		-			(25.5	)


Balance at December 31, 2025	$	(168.5	)	$	(0.3	)	$	(168.8	)

The major categories of plan assets were as follows:


As at	December 31, 2025	December 31, 2024

Cash and cash equivalents	1%	2%
Equity instruments	51%	50%
Debt instruments	45%	46%
Other	3%	2%


	100%	100%

Cash flow information

The Company is required to make contributions equal to current service cost. Contributions for the year ended December 31, 2025 under these regulations were $28.0 million. Contributions for the nine month period ended December 31, 2024 under these regulations were $20.0 million.

The Company’s expected future contributions in respect of its defined benefit pension plans for the fiscal year ending December 31, 2026 is $21.0 million.

Sensitivity of results to actuarial assumptions

The sensitivity of the defined benefit obligation to the key actuarial assumptions is as follows:


	Year ended December 31, 2025			Nine months ended December 31, 2024

Effect of change in discount rate assumption

One percentage point increase	$	(116.6	)	$	(124.0	)

One percentage point decrease	$	138.9		$	148.7

Effect of change in salary scale

One percentage point increase	$	12.2		$	19.1

One percentage point decrease	$	(11.2	)	$	(14.1	)

Effect of change in mortality assumption

Set forward one year	$	34.1		$	35.9

Set back one year	$	(34.9	)	$	(33.2	)

The discount rate sensitivities presented above are estimates based on plan durations. The defined benefit obligation and the current service cost have an implied duration of 10 and 17 years, respectively at current discount rates.

If the returns on plan assets had been 10% lower than the actual returns of plan assets experienced in the year ended December 31, 2025, the actuarial gain immediately recognized in other comprehensive loss would have decreased by approximately $110.0 million.

If the returns on plan assets had been 10% lower than the actual returns of plan assets experienced in the nine month period ended December 31, 2024, the actuarial gain immediately recognized in other comprehensive loss would have decreased by approximately $105.0 million.

Material Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information About Estimated Useful life

Depreciation is calculated by the straight-line method based on estimated useful lives as follows:


Category of Property, Plant and Equipment		Range of Estimated Useful Life

Buildings		5 to 30 years

Machinery and equipment		5 to 40 years

Vehicles		6 to 12 years

Computer hardware		3 to 5 years

Other Post-Employment Benefits - Summary of Other Comprehensive Income (Loss) in the Consolidated Statements of Changes in Shareholder's Equity (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Statement [Line Items]
Beginning balance , Actuarial (gain) loss immediately recognized	$ (73.5)	$ (98.8)
Actuarial (gain) loss immediately recognized , Actuarial gain immediately recognized	(25.3)	(8.8)
Ending balance , Actuarial gain immediately recognized	(98.8)	(107.6)
Beginning balance , Tax effect	0.0	0.0
Actuarial loss immediately recognized , Tax effect	0.0	0.0
Ending balance , Tax effect	0.0	0.0
Beginning balance , Actuarial (gain) immediately recognized, net of tax	(73.5)	(98.8)
Actuarial gain immediately recognized , Actuarial (gain) immediately recognized, net of tax	(25.3)	(8.8)
Ending balance , Actuarial (gain) immediately recognized, net of tax	$ (98.8)	$ (107.6)

Other Long-Term Liabilities (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed about Other Long term Liabilities


As at,	December 31, 2025		December 31, 2024

The carrying amount of the following other long term liabilities:
Accrued interest payable, Provincial MENDM Loan	$	6.2	$	7.3
Financing arrangements		21.6		12.6
LETL governmental loan benefit		38.6		-
Long-term disability plan obligation		1.1		1.1
Long-term portion of lease liability		1.4		2.2
Legal settlement		1.7		3.5


	$	70.7	$	26.7

Senior Secured Lien Notes (Table)

12 Months Ended

Dec. 31, 2025

Senior Secured Lien Notes [Abstract]

Summary of Transaction Costs


As at,	December 31, 2025			December 31, 2024

The carrying amount of:

Senior Secured Lien Notes, due April 15, 2029	$	483.8		$	507.8

Less: unamortized transaction costs		(7.2	)		(9.4	)


	$	476.6		$	498.4

Share-Based Payment Compensation Liability - Additional Information (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024 CAD ($)	Dec. 31, 2025 CAD ($)	Dec. 31, 2025 $ / shares
Shared Based Payment Compensation Liability [Line Items]
Loss (gain) on earn out liability	$ 5.3	$ 19.8
Estimated fair value of other equity instruments outstanding in a share based payment arrangement \| $ / shares			$ 4.1
Number of instruments other equity instruments settled value	$ 2.1

Other Post-Employment Benefits - Summary of statements of financial position (Detail)	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Statement [Line Items]
Defined benefit obligation	4.85%	4.70%
Current service cost	4.84%	4.81%
Interest cost on benefit obligation	4.79%	4.39%
Interest cost on current service cost	4.85%	4.80%
Health care cost immediate trend rate	4.90%	4.83%
Health care cost immediate trend rate	4.83%	4.76%
Year ultimate health care cost trend rate reached	2040 years	2040 years

Share-Based Compensation - Summary Of Continuity of PSUs (Detail) - shares	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Financial Year 2025 Plan [Member]
Disclosure Of Terms And Conditions Of Performance Share based Payment Arrangement [Line Items]
Dividend equivalents and other adjustments, net of cancellations	(63,146)	(921,434)

Senior Secured Lien Notes

12 Months Ended

Dec. 31, 2025

Senior Secured Lien Notes [Abstract]

Senior Secured Lien Notes

21.	SENIOR SECURED LIEN NOTES

On April 5, 2024, the Company’s indirect wholly-owned subsidiary, ASI, issued an aggregate of US $350.0 million of 9.125% Senior Secured Lien Notes (the “Notes”) due April 15, 2029. The Notes are guaranteed on a senior secured basis by ASI’s immediate parent company and all of ASI’s subsidiaries. Interest payments are due April 15 and October 15, and commenced on October 15, 2024.

Prior to the maturity date, the Company can exercise various rights to redeem the Notes in whole or in part at a specific redemption price. In some cases, the redemption of the Notes is only permitted upon the occurrence of a specific event. Management has determined that these optional redemption features of the Notes represent an embedded derivative. At December 31, 2025, the fair value of the derivative asset of nil (December 31, 2024 - $5.9 million) is presented in other long-term assets in the consolidated statements of financial position.

Underwriter fees and other transaction costs related to the Notes amounted to $10.1 million. Transaction costs are presented as an offset against the Notes in the consolidated statements of financial position, and are being amortized using the effective interest rate method over the life of the facility.


As at,	December 31, 2025			December 31, 2024

The carrying amount of:

Senior Secured Lien Notes, due April 15, 2029	$	483.8		$	507.8

Less: unamortized transaction costs		(7.2	)		(9.4	)


	$	476.6		$	498.4

Tax Receivable

12 Months Ended

Dec. 31, 2025

Tax Receivable [Abstract]

TAXES RECEIVABLE

14.	TAXES RECEIVABLE


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Sales taxes receivable	$	5.1	$	27.7

Income taxes receivable		201.8		56.6


	$	206.9	$	84.3

Severance Costs

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Severance Costs

12.	SEVERANCE COSTS

On September 28, 2025, in response to the projected tariff situation affecting Canadian steel exports to the United States, the Company’s Board of Directors approved an operational plan to commence the exit from blast furnace and coke production and to accelerate the transition to EAF steelmaking by December 31, 2025. In connection with this plan, on December 1, 2025 the Company issued layoff notices to 1,005 unionized employees. As a result, an accrual of severance and other employee related costs totalling $45.8 million is presented in the consolidated statements of financial position.

Warrant Liability - Additional Information (Detail)	12 Months Ended
Warrant Liability - Additional Information (Detail)	Dec. 31, 2025 $ / shares shares
Warrant Liability [Line Items]
Class of warrants or rights warrants outstanding \| shares	24,178,999
Warrants estimated fair value per share \| $ / shares	$ 0.075

Basis of Presentation

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Basis of Presentation

2.	BASIS OF PRESENTATION

Statement of compliance

These consolidated financial statements have been prepared in accordance with IFRS

Accounting Standards as issued by the International Accounting Standards Board (“IASB”).

These consolidated financial statements have been approved by the Board of Directors, and authorized for issuance on March 10, 2026.

Functional and presentation currency

The Company and its subsidiaries’ functional currency is the United States dollar (“US dollar”). The US dollar is the currency of the primary economic environment in which the Company and its subsidiaries operate.

For reporting purposes, the consolidated financial statements are presented in millions of Canadian dollars (“$C”). The assets and liabilities are translated into the reporting currency using exchange rates prevailing at the end of each reporting period. Income and expense items are translated at average exchange rates for the reporting period. Exchange differences arising are recognized in

other comprehensive (loss) income and accumulated in equity under the heading ‘Foreign exchange on translation to presentation currency’.

Equity transactions, as disclosed in Note 29, are translated at the historical exchange rates. The resulting net translation adjustment has been recorded in other comprehensive (loss) income for the year.

Tax Receivable (Tables)

12 Months Ended

Dec. 31, 2025

Tax Receivable [Abstract]

Summary of Taxes Receivable


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Sales taxes receivable	$	5.1	$	27.7

Income taxes receivable		201.8		56.6


	$	206.9	$	84.3

Finance Costs (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Detailed Information About Finance Cost Explanatory


	Year ended December 31, 2025		Nine months ended December 31, 2024

Finance costs are comprised of:

Interest on senior secured lien notes (Note 21)	$	43.4	$	31.5

Revolving Credit Facility fees		2.7		1.8

Interest on the Revolving Credit Facility (Note 18)		2.4		-

Interest on Large Enterprise Tariff Loan (LETL) Facilities		0.3		-

Interest on financing arrangement		1.5		0.6

Other interest expense		3.5		7.9

Revaluation of discount rate for environmental liabilities		1.2		0.3

Unwinding of issuance costs of debt facilities (Note 18, 22, 26 ) and accretion of governmental loan benefits and discounts on environmental liabilities		17.1		13.4


	$	72.1	$	55.5

Warrant Liability

12 Months Ended

Dec. 31, 2025

Warrant Liability [Abstract]

Warrant Liability

34.	IPO WARRANT LIABILITY

As at December 31, 2025, 24,178,999

IPO Warrants remain outstanding with an estimated fair value of US $

0.075

per IPO Warrant based on the market price of the IPO Warrants, for which the Company recognized a liability of $

2.5 million (US $1.8 million) (December 31, 2024 - $52.2 million; US $36.3 million). For the year ended December 31, 2025, a gain of $49.0

million on change in the fair value of the IPO Warrant liability is presented in the consolidated statements of net loss. For the year ended December 31, 2024, a loss of $

4.0

million on change in the fair value of the IPO Warrant liability is presented in the consolidated statements of net loss. The IPO Warrants will expire on October 19, 2026.

Interest On Pension And Other Post-Employment Benefit Obligations (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Interest On Pension And Other Post Employment Benefit Obligations


	Year ended December 31, 2025		Nine months ended December 31, 2024

Interest on pension and other post-employment benefit obligations is comprised of:

Interest on defined benefit pension obligation (Note 23)	$	7.0	$	8.1

Interest on other post-employment benefit obligation (Note 24)		8.8		8.0


	$	15.8	$	16.1

Interest On Pension And Other Post-Employment Benefit Obligations

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Interest On Pension And Other Post-Employment Benefit Obligations

11.	INTEREST ON PENSION AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS


	Year ended December 31, 2025		Nine months ended December 31, 2024

Interest on pension and other post-employment benefit obligations is comprised of:

Interest on defined benefit pension obligation (Note 23)	$	7.0	$	8.1

Interest on other post-employment benefit obligation (Note 24)		8.8		8.0


	$	15.8	$	16.1

Share-Based Compensation - Additional Information (Detail) - CAD ($) shares in Millions, $ in Millions		9 Months Ended	12 Months Ended
	Oct. 19, 2021	Dec. 31, 2024	Dec. 31, 2025
Statement [Line Items]
Contributed Surplus Deficit Reserve for share-based payment compensation expense		$ 1.7	$ 2.1
Longterm Incentive Plan [Member]
Statement [Line Items]
Maximum number of common shares that may be awarded under Omnibus Plan	8.8

Taxes Payable and Accrued Taxes (Tables)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Summary of Taxes Payable and Accrued Taxes


As at,	December 31, 2025		December 31, 2024

The carrying amount of:

Payroll taxes payable	$	4.1	$	7.0

Sales taxes payable		1.6		1.8

Carbon tax accrual		27.0		32.8


	$	32.7	$	41.6

Other Income - Additional Information (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Other Income [Abstract]
Proceeds form insurance	$ 32.1	$ 75.0
Insurance Receivable		$ 6.5

Accounts Payable and Accrued Liabilities - Summary of Accounts Payable and Accrued Liabilities (Detail) - CAD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Disclosure of Detailed Information About Accounts Payable and Accrued Liabilities [Line Items]
Wages and accrued vacation payable	$ 46.7	$ 51.9
Accounts Payable and Accrued Liabilities Current	$ 203.9	$ 319.1

Net Income Per Common Share - Summary of Computation of Basic and Diluted Net Income (Loss) Per Common Share (Detail) - CAD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Text Block [Abstract]
Gain on change in fair value of warrants	$ 0	$ 0
Dilutive effect of warrants, restricted share units and performance share units	0	0

Material Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2025

Text Block [Abstract]

Retirement benefit costs

The Company provides pensions and certain health care, dental care, life insurance and other benefits for certain retired employees pursuant to Company policy. For defined benefit pension plans and other post-employment benefits, the defined benefit cost is actuarially determined on an annual basis by independent actuaries using the projected unit credit method. Remeasurement comprising of actuarial gains and losses, the effect of the asset ceiling and the return on plan assets (excluding interest) are recognized immediately in the consolidated statements of financial position with a charge to other comprehensive (loss) income in the period in which they occur. The Company has elected to transfer those amounts recognized in other comprehensive (loss) income to a separate reserve within equity.

Net-interest

is calculated by applying the discount rate to the net defined benefit liability. Defined benefit and other post-employment benefit costs are split into three categories:

●

service cost, past-service cost, gains and losses on curtailments and settlements;

●

net interest expense; and

●

remeasurement.

The Company recognizes the first two components of defined benefit costs in profit or loss in its consolidated statements of net (loss) income: service cost, past service cost, gains and losses on curtailments and settlements in Cost of sales and Administrative and selling expenses; and net interest expense in Interest on pension and other post-employment benefit obligations. The determination of a benefit expense requires assumptions such as the discount rate, the expected mortality, the expected rate of future compensation increases and the expected healthcare cost trend rate. Actual results will differ from estimated results which are based on these assumptions.

The asset or liability recognized in the consolidated statements of financial position represents the actual plan situation in the Company’s defined benefit and other post-employment benefit plans. All actuarial gains and losses that arise in calculating the present value of the defined benefit obligation and the plan assets, the remeasurement components, are recognized immediately in other comprehensive (loss) income. Any defined benefit asset resulting from this calculation is limited to the present value of any economic benefit in the form of refunds from the plan or reduction in future contributions to the plan.

Payments to defined contribution retirement benefit plans are recognized as an expense when employees have rendered service entitling them to the contributions.

Short-term benefits

Short-term employee benefit obligations are measured on an undiscounted basis and are expensed as the related service is provided. A liability is recognized for the amount expected to be paid under short-term cash bonus or profit-sharing plans if the Company has a present legal or constructive obligation to pay this amount as a result of past service provided by the employee and the obligation can be estimated reliably.

Comprehensive Income

Comprehensive (Loss) Income

Other comprehensive (loss) income (“OCI”) includes foreign exchange gain or loss on translation to the Company’s presentation currency from the US Dollar functional currency. OCI includes actuarially determined gains and losses on post employment benefits offered to certain employees and the effect of any limits applied to the defined benefit asset. Comprehensive (loss) income is composed of net (loss) income and OCI.

Accumulated OCI is a separate component of Shareholders’ Equity which includes the accumulated balances of all components of OCI which are recognized in comprehensive income but excluded from net (loss) income.

Standards and Interpretations issued and not yet adopted

Presentation and Disclosure in Financial Statements

In April 2024, the IASB issued IFRS 18,

Presentation and Disclosure in Financial Statements

. IFRS 18 replaces IAS 1,

Presentation of Financial Statements

and sets out requirements for the presentation and disclosure of information in general purpose financial statements. The standard applies to annual reporting periods beginning on or after January 1, 2027 and is to be applied retrospectively, with early adoption permitted. The Company is currently assessing the impact on the consolidated financial statements.

Amendments to the Classification and Measurement of Financial Instruments

In May 2024, the IASB issued Amendments to the Classification and Measurement of Financial Instruments (Amendments to IFRS 9 and IFRS 7). These amendments updated classification and measurement requirements in IFRS 9 Financial Instruments and related disclosure requirements in IFRS 7 Financial Instruments: Disclosures. The IASB clarified the recognition and derecognition date of certain financial assets and liabilities, and amended the requirements related to settling financial liabilities using an electronic payment system. It also clarified how to assess the contractual cash flow characteristics of financial assets in determining whether they meet the solely payments of principal and interest criterion, including financial assets that have environmental, social and corporate governance (ESG)-linked features and other similar contingent features. The IASB added disclosure requirements for financial instruments with contingent features that do not relate directly to basic lending risks and costs, and amended disclosures relating to equity instruments designated at fair value through other comprehensive (loss) income. The amendments apply to annual reporting periods beginning on or after January 1, 2026 with early application permitted. The Company is currently assessing the impact on the consolidated financial statements.