Summary of Significant Accounting Policies - Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation and Reporting The consolidated financial statements include the accounts of ATI Inc. and its subsidiaries. The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. The results for the Shanghai STAL Precision Stainless Steel Company Limited (STAL) are reported on a one month lag. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting, whereby ATI’s carrying value of the equity method investment on the consolidated balance sheet is the capital investment and any undistributed profit or loss. The investments are classified in other (noncurrent) assets on the consolidated balance sheet. The profit or loss attributable to ATI from equity method investments is included in the consolidated statements of operations as a component of Other (non-operating) income (expense). See Note 7 for further explanation of the Company’s joint ventures. Intercompany accounts and transactions have been eliminated. Unless the context requires otherwise, “ATI” and the “Company” refer to ATI Inc. and its subsidiaries.
Fiscal Year	Fiscal Year The Company follows a 4-4-5 or 5-4-4 fiscal calendar, whereby each fiscal quarter consists of thirteen weeks grouped into two four-week months and one five-week month, and its fiscal year ends on the Sunday closest to December 31. Unless otherwise stated, references to years in this Annual Report on Form 10-K relate to fiscal years, rather than calendar years. Fiscal years 2023, 2022 and 2021 ended on December 31, 2023, January 1, 2023 and January 2, 2022, respectively. All fiscal years presented include 52 weeks of operations. The dates for prior fiscal years have been revised to more precisely reflect the exact day of the year end periods for these fiscal years given our 4-4-5 or 5-4-4 calendar.
Use of Estimates	Risks and Uncertainties and Use of Estimates The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable.
Concentration Risks	The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets.
Change in Accounting Principle	Change in Accounting Principle During the fourth quarter of fiscal year 2023, the Company voluntarily changed the method of accounting for recognizing actuarial gains and losses for its defined benefit pension plans. Under the accounting method change, remeasurement of projected benefit obligation and plan assets for defined benefit pension plans are immediately recognized in earnings through net periodic pension benefit cost within nonoperating retirement benefit expense on the consolidated statements of operations, with pension plans to be remeasured annually in the fourth quarter or on an interim basis as triggering events require remeasurement. Prior to this accounting method change, the Company deferred the recognition of these gains and losses in accumulated other comprehensive loss on the consolidated balance sheet. The accumulated actuarial gains/losses were then amortized into net periodic benefit costs within nonoperating retirement benefit expense on the consolidated statement of operations over the average expected remaining life of plan participants. While the historical accounting principle was acceptable, we believe that the current accounting policy is preferable because it provides a better representation of the operating results of the Company and the economic performance of plan assets in relation to the measurement of its benefit obligations for the period. The change in accounting will more clearly reflect the current period impact of the Company’s pension asset investment strategy to readers of the financial statements. This change has been applied to all defined benefit pension plans on a retrospective basis for all prior periods presented, and as of January 4, 2021, resulted in a cumulative effect decrease to retained earnings of $1.07 billion with a corresponding offset to accumulated other comprehensive loss.
Cash Equivalents and Investments	Cash and Cash Equivalents Cash equivalents are highly liquid investments that are readily convertible to cash with original maturities of three months or less.
Accounts Receivable	Accounts Receivable Accounts receivable are presented net of a reserve for doubtful accounts of $3.2 million and $7.7 million at December 31, 2023 and January 1, 2023, respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. The Company’s accounts receivable reserves are determined based on expected credit losses. Amounts are written-off against the reserve in the period it is determined that the receivable is uncollectible.
Inventories	Inventories Inventories are stated at the lower of cost (first-in, first-out (FIFO) and average cost methods) or net realizable value. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. The term net realizable value is defined as estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. It is the Company’s general policy to write-down to scrap value any inventory that is identified as slow-moving or aged more than twelve months, subject to sales, backlog and anticipated order considerations. In some instances this aging criterion is up to twenty-four months. Inventory valuation reserves also include amounts pertaining to intercompany profit elimination between different subsidiaries.
Long-Lived Assets	Long-Lived Assets Property, plant and equipment are recorded at cost, including capitalized interest, and include long-lived assets acquired under finance leases. Depreciation is primarily recorded using the straight-line method. The Company periodically reviews estimates of useful life and production capacity assigned to new and in service assets. Significant enhancements, including major maintenance activities that extend the lives of property and equipment, are capitalized. Costs related to repairs and maintenance are charged to expense in the period incurred. The cost and related accumulated depreciation of property and equipment retired or disposed of are removed from the accounts and any related gains or losses are included in income. The Company monitors the recoverability of the carrying value of its long-lived assets. An impairment charge is recognized when an indicator of impairment occurs and the expected net undiscounted future cash flows from an asset’s use (including any proceeds from disposition) are less than the asset’s carrying value and the asset’s carrying value exceeds its fair value. If an impairment loss is recognized, the adjusted carrying value of the long-lived asset is its new cost basis and this new cost basis is depreciated over the remaining useful life of the asset. Assets to be disposed of by sale are stated at the lower of their fair values or carrying amounts and depreciation is no longer recognized.
Leases	Leases The Company classifies leases as either operating or financing, and records a right-of-use (ROU) asset and a lease liability on the consolidated balance sheets as further discussed below. The lease liability is equal to the present value of the minimum lease payments for the term of the lease, including any optional renewal periods determined to be reasonably certain to be exercised, using the discount rate determined at lease commencement. This discount rate is the rate implicit in the lease, if known; otherwise, the incremental borrowing rate (IBR) for the expected lease term is used. The Company’s IBRs approximate the rate the Company would have to pay to borrow on a collateralized basis over a similar term at lease inception. The ROU asset is equal to the initial measurement of the lease liability plus any lease payments made to the lessor at or before the commencement date and any unamortized initial direct costs incurred by the lessee, less any unamortized lease incentives received. The Company has elected to not separate lease components from non-lease components for all asset classes, and has made an accounting policy election to apply the short-term exception, which does not require the capitalization of leases with terms of 12 months or less. The Company has lease contracts for real property and machinery and equipment. At inception of a contract, the Company determines whether the contract is or contains a lease. If the Company has a right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the asset, then the contract contains a lease. Several of the Company’s real property lease contracts include options to extend the lease term, and the Company reassesses the likelihood of renewal on at least an annual basis. In addition, several real property leases include variable lease payments, for items such as common area maintenance and utilities, which are expensed as incurred as variable lease expense. There are two types of leases: operating leases and finance leases. Lease classification is determined at lease commencement. A finance lease exists when specific criteria are met that indicate that all the risk and rewards related to the leased assets are transferred to the lessee. All other leases not meeting the finance lease criteria are classified as operating leases. Operating lease expense is recognized on a straight-line basis on the consolidated statement of operations. Finance leases have front-loaded expense recognition which is reported as amortization expense and interest expense on the consolidated statement of operations. ROU assets for operating leases are classified in other long-term assets, and ROU assets for finance leases are classified in property, plant and equipment on the consolidated balance sheet. For operating leases, short-term lease liabilities are classified in other current liabilities, and long-term lease liabilities are classified in other long-term liabilities on the consolidated balance sheet. For finance leases, short-term lease liabilities are classified in short-term debt, and long-term lease liabilities are classified in long-term debt on the consolidated balance sheet. On the cash flow statement, payments for operating leases are classified as operating activities. Payments for finance leases are classified as a financing activity, with the exception of the interest component of the payment which is classified as an operating activity.
Goodwill	Goodwill Goodwill is reviewed annually for impairment, or more frequently if impairment indicators arise. The review for goodwill impairment requires a comparison of the fair value of each reporting unit that has goodwill associated with its operations with its carrying amount, including goodwill. If this comparison reflects impairment, then the loss would be measured as the excess of the carrying value over the calculated fair value. Generally accepted accounting principles provide the option to qualitatively assess goodwill for impairment before completing a quantitative assessment. Under the qualitative approach, if, after assessing the totality of events or circumstances, including both macroeconomic, industry and market factors, and entity-specific factors, the Company determines it is likely (more likely than not) that the fair value of a reporting unit is greater than its carrying amount, then the quantitative impairment analysis is not required. The quantitative assessment may be performed each year for a reporting unit at the Company’s option without first performing a qualitative assessment. The Company’s quantitative assessment of goodwill for possible impairment includes estimating the fair market value of a reporting unit which has goodwill associated with its operations using discounted cash flow and multiples of cash earnings valuation techniques, plus valuation comparisons to recent public sale transactions of similar businesses, if any. These impairment assessments and valuation methods require the Company to make estimates and assumptions regarding revenue growth, changes in working capital and capital expenditures, selling prices and profitability that drive cash flows, and the weighted average cost of capital. Many of these assumptions are determined by reference to market participants identified by the Company. Although management believes that the estimates and assumptions used were reasonable, actual results could differ from those estimates and assumptions. Other events and changes in circumstances may also require goodwill to be tested for impairment between annual measurement dates. While a decline in stock price and market capitalization is not specifically cited as a goodwill impairment indicator, a company’s stock price and market capitalization should be considered in determining whether it is more likely than not that the fair value of a reporting unit is less that its carrying value. Additionally, a significant decline in a company’s stock price may suggest that an adverse change in the business climate may have caused the fair value of one or more reporting units to fall below carrying value. A sustained decline in market capitalization below book value may be determined to require an interim goodwill impairment review.
Environmental	Environmental Costs that mitigate or prevent future environmental contamination or extend the life, increase the capacity or improve the safety or efficiency of property utilized in current operations are capitalized. Other costs that relate to current operations or an existing condition caused by past operations are expensed. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable, but generally not later than the completion of the feasibility study or the Company’s recommendation of a remedy or commitment to an appropriate plan of action. The accruals are reviewed periodically and, as investigations and remediations proceed, adjustments of the accruals are made to reflect new information as appropriate. Accruals for losses from environmental remediation obligations are not discounted to their present value. The accruals are not reduced by possible recoveries from insurance carriers or other third parties, but do reflect allocations among potentially responsible parties (PRPs) at Federal Superfund sites or similar state-managed sites after an assessment is made of the likelihood that such parties will fulfill their obligations at such sites and after appropriate cost-sharing or other agreements are entered. The measurement of environmental liabilities by the Company is based on currently available facts, present laws and regulations, and current technology. Such estimates take into consideration the Company’s prior experience in site investigation and remediation, the data concerning cleanup costs available from other companies and regulatory authorities, and the professional judgment of the Company’s environmental experts in consultation with outside environmental specialists, when necessary. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable. In many cases, however, the Company is not able to determine whether it is liable or, if liability is probable, to reasonably estimate the loss or range of loss. Estimates of the Company’s liability remain subject to additional uncertainties, including the nature and extent of site contamination, available remediation alternatives, the extent of corrective actions that may be required, and the number, participation, and financial condition of other potentially responsible parties (PRPs). The Company adjusts its accruals to reflect new information as appropriate. Future adjustments could have a material adverse effect on the Company’s consolidated results of operations in a given period, but the Company cannot reliably predict the amounts of such future adjustments.
Foreign Currency Translation	Foreign Currency Translation Assets and liabilities of international operations are translated into U.S. dollars using fiscal year-end exchange rates, while revenues and expenses are translated at average exchange rates during the period. The resulting net translation adjustments are recorded as a component of accumulated other comprehensive income (loss) in stockholders’ equity.
Sales Recognition	Sales Recognition The following is the Company’s accounting policy as it relates to Accounting Standards Codification Topic 606 (ASC 606), Contracts with Revenue from Customers. This guidance provides a five-step analysis of transactions to determine when and how revenue is recognized, and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The following is the Company’s accounting policy as it relates to the five-step analysis for revenue recognition: 1.Identify the contract: The Company has determined that the contract with the customer is established when the customer purchase order is accepted or acknowledged. Long-term agreements (LTAs), which typically extend multiple years, are used by the Company and certain of its customers for its specialty materials, in the form of mill products, powders, parts and components, to reduce their supply uncertainty. While these LTAs generally define commercial terms including pricing, termination clauses and other contractual requirements, they do not represent the contract with the customer. 2.Identify the performance obligation in the contract: When the Company accepts or acknowledges the customer purchase order, the type of good or service is defined on a line by line basis. Individual performance obligations are established by virtue of the individual line items identified on the sales order acknowledgment at the time of issuance. Generally, the Company’s revenue relates to the sale of goods and contains a single performance obligation for each distinct good. Conversion services that transform customer-owned inventory to a different dimension, product form, and/or changed mechanical properties are classified as “goods”. 3.Determine the transaction price: Pricing is also defined on a sales order acknowledgment on a line item basis and includes an estimate of variable consideration when required by the terms of the individual customer contract. Variable consideration is when the selling price of the good is not known or is subject to adjustment under certain conditions. Types of variable consideration may include volume discounts, customer rebates and surcharges. ATI also provides assurances that goods or services will meet the product specifications contained within the acknowledged customer contract. As such, returns and refunds reserves are estimated based upon past product line history or, at certain locations, on a claim by claim basis. 4.Allocate the transaction price to the performance obligation: Since a customer contract generally contains only one performance obligation, this step of the analysis is generally not applicable to the Company. 5.Recognize revenue when or as the performance obligation is satisfied: Performance obligations generally occur at a point in time and are satisfied when control passes to the customer. For most transactions, control passes at the time of shipment in accordance with agreed upon delivery terms. On occasion, shipping and handling charges occur after the customer obtains control of the good. When this occurs, the shipping and handling services are considered activities to fulfill the promise to transfer the good. Certain customer agreements involving production of parts and components require revenue to be recognized over time due to there being no alternative use for the product without significant economic loss and an enforceable right to payment including a normal profit margin from the customer in the event of contract termination. The Company uses an input method for determining the amount of revenue, and associated standard cost, to recognize over-time revenue, cost and gross margin for these customer agreements. The input methods used for these agreements include costs incurred and labor hours expended, both of which give an accurate representation of the progress made toward complete satisfaction of that particular performance obligation. Contract assets are recognized when ATI’s conditional right to consideration for goods or services have transferred to the customer. A conditional right indicates that additional performance obligations associated with the contract are yet to be satisfied. Contract assets are assessed separately for impairment purposes. If ATI’s right to consideration from the customer is unconditional, this asset is accounted for as a receivable and presented separately from other contract assets. A right is unconditional if nothing other than the passage of time is required before payment of that consideration is due. Performance obligations that are recognized as revenue at a point-in-time and are billed to the customer are recognized as accounts receivable. Payment terms vary from customer to customer depending upon credit worthiness, prior payment history and other credit considerations. Contract costs are the incremental costs of obtaining and fulfilling a contract (i.e., costs that would not have been incurred if the contract had not been obtained) to provide goods and services to customers. Contract costs for ATI largely consist of design and development costs for molds, dies and other tools that ATI will own and that will be used in producing the products under the supply arrangement. Contract costs are classified as non-current assets and amortized to expense on a systematic and rational basis over a period consistent with the transfer to the customer of the goods or services to which the asset relates. Contract liabilities are recognized when ATI has received consideration from a customer to transfer goods or services at a future point in time when the Company performs under the contract. Elements of variable consideration discussed above may be recorded as contract liabilities. In addition, progress billings and advance payments from customers for costs incurred to date are also reported as contract liabilities.
Research and Development	Research and Development Research, development and technical service activities are closely interrelated and are directed toward development of new products, improvement of existing products, cost reduction, process improvement and control, quality assurance and control, development of new manufacturing methods, and improvement of existing manufacturing methods. Research and development costs are expensed as incurred. Company funded research and development costs were $20.7 million in fiscal year 2023, $16.3 million in fiscal year 2022, and $16.5 million in fiscal year 2021. Customer funded research and development costs were $1.4 million in fiscal year 2023, $1.4 million in fiscal year 2022, and $3.5 million in fiscal year 2021.
Government Assistance	Government Assistance The Company enters into agreements with U.S. federal agencies, U.S. state and local governments, and foreign governments that provide financial assistance and incentives supporting both new capital projects to expand and enhance manufacturing capabilities and also to sustain and maintain existing operations. Depending on the nature of the government program, the financial impacts may be recorded as a reduction to cost of sales through direct offset of labor and overhead costs or lower depreciation expense, or as a reduction of selling, general and administrative expenses for property tax abatement or other similar categories. Benefits from government assistance are recognized as the activities are incurred, subject to ongoing assessments of meeting other relevant terms such as employment or expenditure levels. In November 2021, ATI entered into an agreement with the U.S. Department of Transportation under the Aviation Manufacturing Jobs Protection (AMJP) program for a grant of up to $22.2 million. The receipt of the award was primarily conditioned upon the Company committing to not furlough or lay off a defined group of employees in the High Performance Materials & Components (HPMC) segment operations during the six-month period of performance between November 2021 and May 2022. The AMJP grant benefit was recognized over the six-month performance period as a reduction to cost of sales in proportion to the compensation expense that the award was intended to defray, with $16.6 million recognized in fiscal year 2022 operating results. Cash receipts from the AMJP program were $11.0 million in fiscal year 2022, and this program is now completed. ATI is a party to various U.S. states’ economic development incentive programs that provide economic benefits in the forms of property tax relief or cash payments to offset capital expenditures. These programs generally include requirements for levels of capital spending and/or employment to qualify for the government assistance. For the fiscal years ended December 31, 2023 and January 1, 2023, these state-level programs reduced selling, general and administrative expenses by $1.4 million and $1.6 million, respectively, and cash receipts were $3.4 million and $2.8 million, respectively. Receivables for ongoing programs are $1.2 million and $3.7 million as of December 31, 2023 and January 1, 2023, respectively.
Stock-based Compensation	Stock-based Compensation The Company accounts for stock-based compensation transactions, such as nonvested restricted stock or stock units and performance equity awards, using fair value. Compensation expense for an award is estimated at the date of grant and is recognized over the requisite service period. Compensation expense is adjusted for equity awards that do not vest because service or performance conditions are not satisfied. However, compensation expense already recognized on plans which vest based solely on the attainment of market conditions, such as total shareholder return measures, is not adjusted based on the award attainment status at the end of the measurement period. Compensation expense is adjusted for estimated forfeitures over the award measurement period.
Income Taxes	Income Taxes The provision for, or benefit from, income taxes includes deferred taxes resulting from temporary differences in income for financial and tax purposes using the liability method. Such temporary differences result primarily from differences in the carrying value of assets and liabilities. Future realization of deferred income tax assets requires sufficient taxable income within the carryback and/or carryforward period available under tax law. The Company evaluates on a quarterly basis whether, based on all available evidence, it is probable that the deferred income tax assets are realizable. Valuation allowances are established when it is estimated that it is more likely than not that the tax benefit of the deferred tax asset will not be realized. The evaluation includes the consideration of all available evidence, both positive and negative, regarding the estimated future reversals of existing taxable temporary differences, estimated future taxable income exclusive of reversing temporary differences and carryforwards, historical taxable income in prior carryback periods if carryback is permitted, and potential tax planning strategies which may be employed to prevent an operating loss or tax credit carryforward from expiring unused. The verifiable evidence such as future reversals of existing temporary differences and the ability to carryback are considered before the subjective sources such as estimated future taxable income exclusive of temporary differences and tax planning strategies. It is the Company’s policy to classify interest and penalties recognized on underpayment of income taxes as income tax expense. It is also the Company’s policy to recognize deferred tax amounts stranded in accumulated other comprehensive income (AOCI), which result from tax rate differences on changes in AOCI balances, as an element of income tax expense in the period that the related balance sheet item associated with the AOCI balance ceases to exist. In the case of derivative financial instruments accounted for as hedges, or marketable securities, ATI uses the portfolio method where the stranded deferred tax amount is recognized when all items of a particular category, such as cash flow hedges of a particular risk such as a foreign currency hedge, are settled. In the case of defined benefit pension and other postretirement benefit plans, the stranded deferred tax balance is recognized as an element of income tax expense in the period the benefit plan is extinguished or divested.
Net Income Per Common Share	Net Income Per Common Share Basic and diluted net income per share are calculated by dividing the net income available to common stockholders by the weighted average number of common shares outstanding during the fiscal year. Diluted amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The calculations of all diluted income/loss per share figures for a period exclude the potentially dilutive effect of dilutive share equivalents if there is a net loss since the inclusion in the calculation of additional shares in the net loss per share would result in a lower per share loss and therefore be anti-dilutive.
New Accounting Pronouncements Adopted and Pending Accounting Pronouncements	New Accounting Pronouncements Adopted In August 2020, the Financial Accounting Standards Board (FASB) issued new accounting guidance related to accounting for convertible instruments. Under this new guidance, embedded conversion features are no longer separated from the host contract for convertible instruments with conversion features that are not required to be accounted for as derivatives, or that do not result in substantial premiums accounted for as paid-in capital. As such, a convertible debt instrument will be accounted for as a single liability measured at its amortized cost, as long as no other features require bifurcation and recognition as derivatives. By removing those separation models, the reported interest rate of convertible debt instruments typically will be closer to the coupon interest rate. The new guidance also addresses how convertible instruments are accounted for in the diluted earnings per share calculation, requiring the if-converted method, and requires enhanced disclosures about the terms of convertible instruments and contracts in an entity’s own equity. This new guidance was effective for the Company in fiscal year 2022, with early adoption permitted. The Company early adopted this new accounting guidance related to accounting for convertible instruments effective January 4, 2021 using the modified transition approach with the cumulative effect recognized as an adjustment to the opening balance of retained earnings. This new guidance was applicable to the Company’s 3.5% Convertible Senior Notes due 2025 (the 2025 Convertible Notes) that were issued in June 2020, for which the embedded conversion option was required to be separately accounted for as a component of stockholders’ equity. Upon adoption on January 4, 2021, long-term debt increased by $45.4 million and stockholders’ equity decreased by the same amount, representing the net impact of two adjustments: (1) the $49.8 million value of the embedded conversion, which is net of allocated offering costs, previously classified in additional paid-in capital in stockholders’ equity, and (2) a $4.4 million increase to retained earnings for the cumulative effect of adoption primarily related to the non-cash interest expense recorded in fiscal year 2020 for the amortization of the portion of the 2025 Convertible Notes allocated to stockholders’ equity. Prospectively, the reported interest expense for the 2025 Convertible Notes no longer included the non-cash interest expense of the equity component as required under prior accounting standards and is closer to the 3.5% cash coupon rate. There was no impact to the Company’s earnings per share calculation as it previously applied the if-converted method to the 2025 Convertible Notes given ATI’s flexibility to settle conversions of the 2025 Convertible Notes in cash, shares of ATI’s common stock or a combination thereof, at ATI’s election. In September 2022, the FASB issued new accounting guidance related to disclosures about supplier finance programs. Supplier finance programs allow a buyer to offer its suppliers the option for access to payment in advance of an invoice due date, which is paid by a third-party finance provider or intermediary on the basis of invoices that the buyer has confirmed as valid. This new guidance requires a buyer in a supplier finance program to disclose sufficient information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude, using both qualitative and quantitative information about its supplier finance programs. This new guidance, with the exception of disclosures on rollforward information, is effective for the Company in fiscal year 2023. The Company adopted this new accounting guidance effective January 2, 2023. The rollforward information disclosures are effective for the Company in fiscal year 2024, with early adoption permitted. The Company did not early adopt this guidance. The adoption of these changes did not have an impact on the Company’s consolidated financial statements other than disclosure requirements which are included in Note 9. Pending Accounting Pronouncements In November 2023, the FASB issued new accounting guidance related to segment reporting disclosures. This guidance requires additional disclosures on an annual and interim basis of segment information, including significant segment expenses that are regularly provided to the chief operating decision maker (CODM) and the presentation and composition of other segment items, which is the difference between segment revenue less segment expenses and the measure of segment profit or loss. The guidance also requires that all current segment disclosures required on an annual basis be provided on an interim basis and requires disclosure of the title and position of the CODM and how the CODM uses the reported measure of segment profit or loss in assessing performance and allocating resources. This guidance does not change how an entity identifies its reportable segments. This new guidance for annual disclosures will be effective for the Company for fiscal year 2024 and for interim disclosures will be effective for the Company for fiscal year 2025. The guidance must be applied retrospectively and early adoption is permitted. The Company does not expect to early adopt this guidance and does not expect these changes to have an impact on the Company’s consolidated financial statements other than disclosure requirements. In December 2023, the FASB issued new accounting guidance related to income tax disclosures. This guidance requires entities to disclose specific categories in its annual rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This guidance also requires additional annual disclosures for income taxes paid and requires disaggregation of income before tax, between domestic and foreign, and income tax expense, between federal, state and foreign. This guidance also eliminates several current disclosure requirements related to the nature and estimate of the range of the reasonably possible change in the unrecognized tax benefits balance in the next 12 months and making a statement that an estimate of the range cannot be made and disclosing the cumulative amount of each type of temporary difference when a deferred tax liability is not recognized because of the exceptions to comprehensive recognition of deferred taxes related to subsidiaries and corporate joint ventures. This new guidance will be effective for the Company for fiscal year 2025 and must be applied on a prospective basis with retrospective application permitted. Early adoption of this guidance is also permitted. The Company does not expect to early adopt this guidance and does not expect these changes to have an impact on the Company’s consolidated financial statements other than disclosure requirements.
Asset Retirement Obligations	Asset Retirement Obligations The Company maintains reserves where a legal obligation exists to perform an asset retirement activity and the fair value of the liability can be reasonably estimated. These asset retirement obligations (AROs) include liabilities where the timing and (or) method of settlement may be conditional on a future event, that may or may not be within the control of the entity. At December 31, 2023, the Company had recognized AROs of $18.3 million related to landfill closures, decommissioning costs, facility leases and conditional AROs associated with manufacturing activities using what may be characterized as potentially hazardous materials. Estimates of AROs are evaluated annually in the fourth quarter, or more frequently if material new information becomes known. Accounting for asset retirement obligations requires significant estimation and in certain cases, the Company has determined that an ARO exists, but the amount of the obligation is not reasonably estimable. The Company may determine that additional AROs are required to be recognized as new information becomes available.
Derivative Financial Instruments and Hedging	Derivative Financial Instruments and Hedging As part of its risk management strategy, the Company, from time-to-time, utilizes derivative financial instruments to manage its exposure to changes in raw material prices, energy costs, foreign currencies, and interest rates. In accordance with applicable accounting standards, the Company accounts for most of these contracts as hedges. The Company sometimes uses futures and swap contracts to manage exposure to changes in prices for forecasted purchases of raw materials, such as nickel, and natural gas. Under these contracts, which are generally accounted for as cash flow hedges, the price of the item being hedged is fixed at the time that the contract is entered into and the Company is obligated to make or receive a payment equal to the net change between this fixed price and the market price at the date the contract matures. The majority of ATI’s products are sold utilizing raw material surcharges and index mechanisms. However, as of December 31, 2023, the Company had entered into financial hedging arrangements primarily at the request of its customers, related to firm orders, for an aggregate notional amount of approximately 4 million pounds of nickel with hedge dates through fiscal year 2024. The aggregate notional amount hedged is approximately 6% of a single year’s estimated nickel raw material purchase requirements. These derivative instruments are used to hedge the variability of a selling price that is based on the London Metals Exchange (LME) index for nickel, as well as to hedge the variability of the purchase cost of nickel based on this LME index. Any gain or loss associated with these hedging arrangements is included in sales or cost of sales, depending on whether the underlying risk being hedged was the variable selling price or the variable raw material cost, respectively. At December 31, 2023, the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2023, the company hedged approximately 75% of the Company’s annual forecasted domestic requirements for natural gas for fiscal year 2024 and approximately 35% for fiscal year 2025. While the majority of the Company’s direct export sales are transacted in U.S. dollars, foreign currency exchange contracts are used, from time-to-time, to limit transactional exposure to changes in currency exchange rates for those transactions denominated in a non-U.S. currency. The Company sometimes purchases foreign currency forward contracts that permit it to sell specified amounts of foreign currencies expected to be received from its export sales for pre-established U.S. dollar amounts at specified dates. In addition, the Company may also hedge forecasted capital expenditures and designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. At December 31, 2023, the Company had no significant outstanding foreign currency forward contracts. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. The Company has a $50 million floating-for-fixed interest rate swap that matures in June 2024 which converts a portion of the ABL Term Loan to a 4.21% fixed rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its ABL Term Loan borrowings. The ineffective portion at hedge inception, determined from the fair value of the swap immediately prior to amendment in July 2019, was amortized to interest expense over the initial ABL Term Loan swap maturity date of January 12, 2021. There are no credit risk-related contingent features in the Company’s derivative contracts, and the contracts contained no provisions under which the Company has posted, or would be required to post, collateral. The counterparties to the Company’s derivative contracts were substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible. For derivative financial instruments that are designated as cash flow hedges, the gain or loss on the derivative is reported as a component of other comprehensive income (OCI) and reclassified into earnings in the same period or periods during which the hedged item affects earnings. For derivative financial instruments that are designated as fair value hedges, changes in the fair value of these derivatives are recognized in current period results. There were no outstanding fair value hedges as of December 31, 2023 or January 1, 2023. The cash flow impact for all derivative financial instruments is reported in cash flows provided by operating activities on the consolidated statement of cash flows. The Company did not use net investment hedges for the periods presented.
Pension Plans and Other Postretirement Benefits	The Company has defined contribution retirement plans or defined benefit pension plans covering substantially all employees. Company contributions to defined contribution retirement plans are generally based on a percentage of eligible pay or based on hours worked. Benefits under the defined benefit pension plans are generally based on years of service and/or final average pay. The Company also sponsors several postretirement plans covering certain collectively-bargained salaried and hourly employees. The plans provide health care and life insurance benefits for eligible retirees. In most retiree health care plans, Company contributions towards premiums are capped based on the cost as of a certain date, thereby creating a defined contribution.

Summary of Significant Accounting Policies - Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Principles of Consolidation and Reporting

The consolidated financial statements include the accounts of ATI Inc. and its subsidiaries. The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. The results for the Shanghai STAL Precision Stainless Steel Company Limited (STAL) are reported on a one month lag. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting, whereby ATI’s carrying value of the equity method investment on the consolidated balance sheet is the capital investment and any undistributed profit or loss. The investments are classified in other (noncurrent) assets on the consolidated balance sheet. The profit or loss attributable to ATI from equity method investments is included in the consolidated statements of operations as a component of Other (non-operating) income (expense). See Note 7 for further explanation of the Company’s joint ventures. Intercompany accounts and transactions have been eliminated. Unless the context requires otherwise, “ATI” and the “Company” refer to ATI Inc. and its subsidiaries.

Fiscal Year

The Company follows a 4-4-5 or 5-4-4 fiscal calendar, whereby each fiscal quarter consists of thirteen weeks grouped into two four-week months and one five-week month, and its fiscal year ends on the Sunday closest to December 31. Unless otherwise stated, references to years in this Annual Report on Form 10-K relate to fiscal years, rather than calendar years. Fiscal years 2023, 2022 and 2021 ended on December 31, 2023, January 1, 2023 and January 2, 2022, respectively. All fiscal years presented include 52 weeks of operations. The dates for prior fiscal years have been revised to more precisely reflect the exact day of the year end periods for these fiscal years given our 4-4-5 or 5-4-4 calendar.

Use of Estimates

Risks and Uncertainties and Use of Estimates

The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable.

Concentration Risks

The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets.

Change in Accounting Principle

During the fourth quarter of fiscal year 2023, the Company voluntarily changed the method of accounting for recognizing actuarial gains and losses for its defined benefit pension plans. Under the accounting method change, remeasurement of projected benefit obligation and plan assets for defined benefit pension plans are immediately recognized in earnings through net periodic pension benefit cost within nonoperating retirement benefit expense on the consolidated statements of operations, with pension plans to be remeasured annually in the fourth quarter or on an interim basis as triggering events require remeasurement. Prior to this accounting method change, the Company deferred the recognition of these gains and losses in accumulated other comprehensive loss on the consolidated balance sheet. The accumulated actuarial gains/losses were then amortized into net periodic benefit costs within nonoperating retirement benefit expense on the consolidated statement of operations over the average expected remaining life of plan participants. While the historical accounting principle was acceptable, we believe that the current accounting policy is preferable because it provides a better representation of the

operating results of the Company and the economic performance of plan assets in relation to the measurement of its benefit obligations for the period. The change in accounting will more clearly reflect the current period impact of the Company’s pension asset investment strategy to readers of the financial statements.

This change has been applied to all defined benefit pension plans on a retrospective basis for all prior periods presented, and as of January 4, 2021, resulted in a cumulative effect decrease to retained earnings of $1.07 billion with a corresponding offset to accumulated other comprehensive loss.

Cash Equivalents and Investments

Cash and Cash Equivalents

Cash equivalents are highly liquid investments that are readily convertible to cash with original maturities of three months or less.

Accounts Receivable

Accounts receivable are presented net of a reserve for doubtful accounts of $3.2 million and $7.7 million at December 31, 2023 and January 1, 2023, respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. The Company’s accounts receivable reserves are determined based on expected credit losses. Amounts are written-off against the reserve in the period it is determined that the receivable is uncollectible.

Inventories

Inventories are stated at the lower of cost (first-in, first-out (FIFO) and average cost methods) or net realizable value. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. The term net realizable value is defined as estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation.

The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. It is the Company’s general policy to write-down to scrap value any inventory that is identified as slow-moving or aged more than twelve months, subject to sales, backlog and anticipated order considerations. In some instances this aging criterion is up to twenty-four months. Inventory valuation reserves also include amounts pertaining to intercompany profit elimination between different subsidiaries.

Long-Lived Assets

Property, plant and equipment are recorded at cost, including capitalized interest, and include long-lived assets acquired under finance leases. Depreciation is primarily recorded using the straight-line method. The Company periodically reviews estimates of useful life and production capacity assigned to new and in service assets. Significant enhancements, including major maintenance activities that extend the lives of property and equipment, are capitalized. Costs related to repairs and maintenance are charged to expense in the period incurred. The cost and related accumulated depreciation of property and equipment retired or disposed of are removed from the accounts and any related gains or losses are included in income.

The Company monitors the recoverability of the carrying value of its long-lived assets. An impairment charge is recognized when an indicator of impairment occurs and the expected net undiscounted future cash flows from an asset’s use (including any proceeds from disposition) are less than the asset’s carrying value and the asset’s carrying value exceeds its fair value. If an impairment loss is recognized, the adjusted carrying value of the long-lived asset is its new cost basis and this new cost basis is depreciated over the remaining useful life of the asset. Assets to be disposed of by sale are stated at the lower of their fair values or carrying amounts and depreciation is no longer recognized.

Leases

The Company classifies leases as either operating or financing, and records a right-of-use (ROU) asset and a lease liability on the consolidated balance sheets as further discussed below. The lease liability is equal to the present value of the minimum lease payments for the term of the lease, including any optional renewal periods determined to be reasonably certain to be exercised, using the discount rate determined at lease commencement. This discount rate is the rate implicit in the lease, if known; otherwise, the incremental borrowing rate (IBR) for the expected lease term is used. The Company’s IBRs approximate the rate the Company would have to pay to borrow on a collateralized basis over a similar term at lease inception. The ROU asset is equal to the initial measurement of the lease liability plus any lease payments made to the lessor at or before the commencement date and any unamortized initial direct costs incurred by the lessee, less any unamortized lease incentives received. The Company has elected to not separate lease components from non-lease components for all asset classes, and has made an accounting policy election to apply the short-term exception, which does not require the capitalization of leases with terms of 12 months or less.

The Company has lease contracts for real property and machinery and equipment. At inception of a contract, the Company determines whether the contract is or contains a lease. If the Company has a right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the asset, then the contract contains a lease. Several of the Company’s real property lease contracts include options to extend the lease term, and the Company reassesses the likelihood of renewal on at least an annual basis. In addition, several real property leases include variable lease payments, for items such as common area maintenance and utilities, which are expensed as incurred as variable lease expense.

There are two types of leases: operating leases and finance leases. Lease classification is determined at lease commencement. A finance lease exists when specific criteria are met that indicate that all the risk and rewards related to the leased assets are transferred to the lessee. All other leases not meeting the finance lease criteria are classified as operating leases. Operating lease expense is recognized on a straight-line basis on the consolidated statement of operations. Finance leases have front-loaded expense recognition which is reported as amortization expense and interest expense on the consolidated statement of operations. ROU assets for operating leases are classified in other long-term assets, and ROU assets for finance leases are classified in property, plant and equipment on the consolidated balance sheet. For operating leases, short-term lease liabilities are classified in other current liabilities, and long-term lease liabilities are classified in other long-term liabilities on the consolidated balance sheet. For finance leases, short-term lease liabilities are classified in short-term debt, and long-term lease liabilities are classified in long-term debt on the consolidated balance sheet. On the cash flow statement, payments for operating leases are classified as operating activities. Payments for finance leases are classified as a financing activity, with the exception of the interest component of the payment which is classified as an operating activity.

Goodwill

Goodwill is reviewed annually for impairment, or more frequently if impairment indicators arise. The review for goodwill impairment requires a comparison of the fair value of each reporting unit that has goodwill associated with its operations with its carrying amount, including goodwill. If this comparison reflects impairment, then the loss would be measured as the excess of the carrying value over the calculated fair value.

Generally accepted accounting principles provide the option to qualitatively assess goodwill for impairment before completing a quantitative assessment. Under the qualitative approach, if, after assessing the totality of events or circumstances, including both macroeconomic, industry and market factors, and entity-specific factors, the Company determines it is likely (more likely than not) that the fair value of a reporting unit is greater than its carrying amount, then the quantitative impairment analysis is not required. The quantitative assessment may be performed each year for a reporting unit at the Company’s option without first performing a qualitative assessment. The Company’s quantitative assessment of goodwill for possible impairment includes estimating the fair market value of a reporting unit which has goodwill associated with its operations using discounted cash flow and multiples of cash earnings valuation techniques, plus valuation comparisons to recent public sale transactions of similar businesses, if any. These impairment assessments and valuation methods require the Company to make estimates and assumptions regarding revenue growth, changes in working capital and capital expenditures, selling prices and profitability that drive cash flows, and the weighted average cost of capital. Many of these assumptions are determined by reference to market participants identified by the Company. Although management believes that the estimates and assumptions used were reasonable, actual results could differ from those estimates and assumptions.

Other events and changes in circumstances may also require goodwill to be tested for impairment between annual measurement dates. While a decline in stock price and market capitalization is not specifically cited as a goodwill impairment indicator, a company’s stock price and market capitalization should be considered in determining whether it is more likely than not that the fair value of a reporting unit is less that its carrying value. Additionally, a significant decline in a company’s stock price may suggest that an adverse change in the business climate may have caused the fair value of one or more reporting units to fall below carrying value. A sustained decline in market capitalization below book value may be determined to require an interim goodwill impairment review.

Environmental

Costs that mitigate or prevent future environmental contamination or extend the life, increase the capacity or improve the safety or efficiency of property utilized in current operations are capitalized. Other costs that relate to current operations or an existing condition caused by past operations are expensed. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable, but generally not later than the completion of the feasibility study or the Company’s recommendation of a remedy or commitment to an appropriate plan of action. The accruals are reviewed periodically and, as investigations and remediations proceed, adjustments of the accruals are made to reflect new information as appropriate. Accruals for losses from environmental remediation obligations are not discounted to their present value. The accruals are not reduced by possible recoveries from insurance carriers or other third parties, but do reflect allocations among potentially responsible parties (PRPs) at Federal Superfund sites or similar state-managed sites after an assessment is made of the likelihood that such parties will fulfill their obligations at such sites and after appropriate cost-sharing or other agreements are entered. The measurement of environmental liabilities by the Company is based on currently available facts, present laws and regulations, and current technology. Such estimates take into consideration the Company’s prior experience in site investigation and remediation, the data concerning cleanup costs available from other companies and regulatory authorities, and the professional judgment of the Company’s environmental experts in consultation with outside environmental specialists, when necessary.

Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable. In many cases, however, the Company is not able to determine whether it is liable or, if liability is probable, to reasonably estimate the loss or range of loss. Estimates of the Company’s liability remain subject to additional uncertainties, including the nature and extent of site contamination, available remediation alternatives, the extent of corrective actions that may be required, and the number, participation, and financial condition of other potentially responsible parties (PRPs). The Company adjusts its accruals to reflect new information as appropriate. Future adjustments could have a material adverse effect on the Company’s consolidated results of operations in a given period, but the Company cannot reliably predict the amounts of such future adjustments.

Foreign Currency Translation

Assets and liabilities of international operations are translated into U.S. dollars using fiscal year-end exchange rates, while revenues and expenses are translated at average exchange rates during the period. The resulting net translation adjustments are recorded as a component of accumulated other comprehensive income (loss) in stockholders’ equity.

Sales Recognition

The following is the Company’s accounting policy as it relates to Accounting Standards Codification Topic 606 (ASC 606), Contracts with Revenue from Customers. This guidance provides a five-step analysis of transactions to determine when and how revenue is recognized, and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.

The following is the Company’s accounting policy as it relates to the five-step analysis for revenue recognition:

1.Identify the contract: The Company has determined that the contract with the customer is established when the customer purchase order is accepted or acknowledged. Long-term agreements (LTAs), which typically extend multiple years, are used by the Company and certain of its customers for its specialty materials, in the form of mill products, powders, parts and components, to reduce their supply uncertainty. While these LTAs generally define commercial terms including pricing, termination clauses and other contractual requirements, they do not represent the contract with the customer.

2.Identify the performance obligation in the contract: When the Company accepts or acknowledges the customer purchase order, the type of good or service is defined on a line by line basis. Individual performance obligations are established by virtue of the individual line items identified on the sales order acknowledgment at the time of issuance. Generally, the Company’s revenue relates to the sale of goods and contains a single performance obligation for each distinct good. Conversion services that transform customer-owned inventory to a different dimension, product form, and/or changed mechanical properties are classified as “goods”.

3.Determine the transaction price: Pricing is also defined on a sales order acknowledgment on a line item basis and includes an estimate of variable consideration when required by the terms of the individual customer contract. Variable consideration is when the selling price of the good is not known or is subject to adjustment under certain conditions. Types of variable consideration may include volume discounts, customer rebates and surcharges. ATI also provides assurances that goods or services will meet the product specifications contained within the acknowledged customer contract. As such, returns and refunds reserves are estimated based upon past product line history or, at certain locations, on a claim by claim basis.

4.Allocate the transaction price to the performance obligation: Since a customer contract generally contains only one performance obligation, this step of the analysis is generally not applicable to the Company.

5.Recognize revenue when or as the performance obligation is satisfied: Performance obligations generally occur at a point in time and are satisfied when control passes to the customer. For most transactions, control passes at the time of shipment in accordance with agreed upon delivery terms. On occasion, shipping and handling charges occur after the customer obtains control of the good. When this occurs, the shipping and handling services are considered activities to fulfill the promise to transfer the good.

Certain customer agreements involving production of parts and components require revenue to be recognized over time due to there being no alternative use for the product without significant economic loss and an enforceable right to payment including a normal profit margin from the customer in the event of contract termination. The Company uses an input method for determining the amount of revenue, and associated standard cost, to recognize over-time revenue, cost and gross margin for these customer agreements. The input methods used for these agreements include costs incurred and labor hours expended, both of which give an accurate representation of the progress made toward complete satisfaction of that particular performance obligation.

Contract assets are recognized when ATI’s conditional right to consideration for goods or services have transferred to the customer. A conditional right indicates that additional performance obligations associated with the contract are yet to be satisfied. Contract assets are assessed separately for impairment purposes. If ATI’s right to consideration from the customer is unconditional, this asset is accounted for as a receivable and presented separately from other contract assets. A right is unconditional if nothing other than the passage of time is required before payment of that consideration is due. Performance obligations that are recognized as revenue at a point-in-time and are billed to the customer are recognized as accounts

receivable. Payment terms vary from customer to customer depending upon credit worthiness, prior payment history and other credit considerations.

Contract costs are the incremental costs of obtaining and fulfilling a contract (i.e., costs that would not have been incurred if the contract had not been obtained) to provide goods and services to customers. Contract costs for ATI largely consist of design and development costs for molds, dies and other tools that ATI will own and that will be used in producing the products under the supply arrangement. Contract costs are classified as non-current assets and amortized to expense on a systematic and rational basis over a period consistent with the transfer to the customer of the goods or services to which the asset relates.

Contract liabilities are recognized when ATI has received consideration from a customer to transfer goods or services at a future point in time when the Company performs under the contract. Elements of variable consideration discussed above may be recorded as contract liabilities. In addition, progress billings and advance payments from customers for costs incurred to date are also reported as contract liabilities.

Research and Development

Research, development and technical service activities are closely interrelated and are directed toward development of new products, improvement of existing products, cost reduction, process improvement and control, quality assurance and control, development of new manufacturing methods, and improvement of existing manufacturing methods. Research and development costs are expensed as incurred. Company funded research and development costs were $20.7 million in fiscal year 2023, $16.3 million in fiscal year 2022, and $16.5 million in fiscal year 2021. Customer funded research and development costs were $1.4 million in fiscal year 2023, $1.4 million in fiscal year 2022, and $3.5 million in fiscal year 2021.

Government Assistance

The Company enters into agreements with U.S. federal agencies, U.S. state and local governments, and foreign governments that provide financial assistance and incentives supporting both new capital projects to expand and enhance manufacturing capabilities and also to sustain and maintain existing operations. Depending on the nature of the government program, the financial impacts may be recorded as a reduction to cost of sales through direct offset of labor and overhead costs or lower depreciation expense, or as a reduction of selling, general and administrative expenses for property tax abatement or other similar categories. Benefits from government assistance are recognized as the activities are incurred, subject to ongoing assessments of meeting other relevant terms such as employment or expenditure levels.

In November 2021, ATI entered into an agreement with the U.S. Department of Transportation under the Aviation Manufacturing Jobs Protection (AMJP) program for a grant of up to $22.2 million. The receipt of the award was primarily conditioned upon the Company committing to not furlough or lay off a defined group of employees in the High Performance Materials & Components (HPMC) segment operations during the six-month period of performance between November 2021 and May 2022. The AMJP grant benefit was recognized over the six-month performance period as a reduction to cost of sales in proportion to the compensation expense that the award was intended to defray, with $16.6 million recognized in fiscal year 2022 operating results. Cash receipts from the AMJP program were $11.0 million in fiscal year 2022, and this program is now completed.

ATI is a party to various U.S. states’ economic development incentive programs that provide economic benefits in the forms of property tax relief or cash payments to offset capital expenditures. These programs generally include requirements for levels of capital spending and/or employment to qualify for the government assistance. For the fiscal years ended December 31, 2023 and January 1, 2023, these state-level programs reduced selling, general and administrative expenses by $1.4 million and $1.6 million, respectively, and cash receipts were $3.4 million and $2.8 million, respectively. Receivables for ongoing programs are $1.2 million and $3.7 million as of December 31, 2023 and January 1, 2023, respectively.

Stock-based Compensation

The Company accounts for stock-based compensation transactions, such as nonvested restricted stock or stock units and performance equity awards, using fair value. Compensation expense for an award is estimated at the date of grant and is recognized over the requisite service period. Compensation expense is adjusted for equity awards that do not vest because service or performance conditions are not satisfied. However, compensation expense already recognized on plans which vest based solely on the attainment of market conditions, such as total shareholder return measures, is not adjusted based on the award attainment status at the end of the measurement period. Compensation expense is adjusted for estimated forfeitures over the award measurement period.

Income Taxes

The provision for, or benefit from, income taxes includes deferred taxes resulting from temporary differences in income for financial and tax purposes using the liability method. Such temporary differences result primarily from differences in the carrying value of assets and liabilities. Future realization of deferred income tax assets requires sufficient taxable income within the carryback and/or carryforward period available under tax law.

The Company evaluates on a quarterly basis whether, based on all available evidence, it is probable that the deferred income tax assets are realizable. Valuation allowances are established when it is estimated that it is more likely than not that the tax benefit of the deferred tax asset will not be realized. The evaluation includes the consideration of all available evidence, both positive and negative, regarding the estimated future reversals of existing taxable temporary differences, estimated future taxable income exclusive of reversing temporary differences and carryforwards, historical taxable income in prior carryback periods if carryback is permitted, and potential tax planning strategies which may be employed to prevent an operating loss or tax credit carryforward from expiring unused. The verifiable evidence such as future reversals of existing temporary differences and the ability to carryback are considered before the subjective sources such as estimated future taxable income exclusive of temporary differences and tax planning strategies.

It is the Company’s policy to classify interest and penalties recognized on underpayment of income taxes as income tax expense. It is also the Company’s policy to recognize deferred tax amounts stranded in accumulated other comprehensive income (AOCI), which result from tax rate differences on changes in AOCI balances, as an element of income tax expense in the period that the related balance sheet item associated with the AOCI balance ceases to exist. In the case of derivative financial instruments accounted for as hedges, or marketable securities, ATI uses the portfolio method where the stranded deferred tax amount is recognized when all items of a particular category, such as cash flow hedges of a particular risk such as a foreign currency hedge, are settled. In the case of defined benefit pension and other postretirement benefit plans, the stranded deferred tax balance is recognized as an element of income tax expense in the period the benefit plan is extinguished or divested.

Net Income Per Common Share

Basic and diluted net income per share are calculated by dividing the net income available to common stockholders by the weighted average number of common shares outstanding during the fiscal year. Diluted amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The calculations of all diluted income/loss per share figures for a period exclude the potentially dilutive effect of dilutive share equivalents if there is a net loss since the inclusion in the calculation of additional shares in the net loss per share would result in a lower per share loss and therefore be anti-dilutive.

New Accounting Pronouncements Adopted and Pending Accounting Pronouncements

New Accounting Pronouncements Adopted

In August 2020, the Financial Accounting Standards Board (FASB) issued new accounting guidance related to accounting for convertible instruments. Under this new guidance, embedded conversion features are no longer separated from the host contract for convertible instruments with conversion features that are not required to be accounted for as derivatives, or that do not result in substantial premiums accounted for as paid-in capital. As such, a convertible debt instrument will be accounted for as a single liability measured at its amortized cost, as long as no other features require bifurcation and recognition as derivatives. By removing those separation models, the reported interest rate of convertible debt instruments typically will be closer to the coupon interest rate. The new guidance also addresses how convertible instruments are accounted for in the diluted earnings per share calculation, requiring the if-converted method, and requires enhanced disclosures about the terms of convertible instruments and contracts in an entity’s own equity. This new guidance was effective for the Company in fiscal year 2022, with early adoption permitted.

The Company early adopted this new accounting guidance related to accounting for convertible instruments effective January 4, 2021 using the modified transition approach with the cumulative effect recognized as an adjustment to the opening balance of retained earnings. This new guidance was applicable to the Company’s 3.5% Convertible Senior Notes due 2025 (the 2025 Convertible Notes) that were issued in June 2020, for which the embedded conversion option was required to be separately accounted for as a component of stockholders’ equity. Upon adoption on January 4, 2021, long-term debt increased by $45.4 million and stockholders’ equity decreased by the same amount, representing the net impact of two adjustments: (1) the $49.8 million value of the embedded conversion, which is net of allocated offering costs, previously classified in additional paid-in capital in stockholders’ equity, and (2) a $4.4 million increase to retained earnings for the cumulative effect of adoption primarily related to the non-cash interest expense recorded in fiscal year 2020 for the amortization of the portion of the 2025 Convertible Notes allocated to stockholders’ equity. Prospectively, the reported interest expense for the 2025 Convertible Notes no longer included the non-cash interest expense of the equity component as required under prior accounting standards and is closer to the 3.5% cash coupon rate. There was no impact to the Company’s earnings per share calculation as it

previously applied the if-converted method to the 2025 Convertible Notes given ATI’s flexibility to settle conversions of the 2025 Convertible Notes in cash, shares of ATI’s common stock or a combination thereof, at ATI’s election.

In September 2022, the FASB issued new accounting guidance related to disclosures about supplier finance programs. Supplier finance programs allow a buyer to offer its suppliers the option for access to payment in advance of an invoice due date, which is paid by a third-party finance provider or intermediary on the basis of invoices that the buyer has confirmed as valid. This new guidance requires a buyer in a supplier finance program to disclose sufficient information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude, using both qualitative and quantitative information about its supplier finance programs. This new guidance, with the exception of disclosures on rollforward information, is effective for the Company in fiscal year 2023. The Company adopted this new accounting guidance effective January 2, 2023. The rollforward information disclosures are effective for the Company in fiscal year 2024, with early adoption permitted. The Company did not early adopt this guidance. The adoption of these changes did not have an impact on the Company’s consolidated financial statements other than disclosure requirements which are included in Note 9.

Pending Accounting Pronouncements

In November 2023, the FASB issued new accounting guidance related to segment reporting disclosures. This guidance requires additional disclosures on an annual and interim basis of segment information, including significant segment expenses that are regularly provided to the chief operating decision maker (CODM) and the presentation and composition of other segment items, which is the difference between segment revenue less segment expenses and the measure of segment profit or loss. The guidance also requires that all current segment disclosures required on an annual basis be provided on an interim basis and requires disclosure of the title and position of the CODM and how the CODM uses the reported measure of segment profit or loss in assessing performance and allocating resources. This guidance does not change how an entity identifies its reportable segments. This new guidance for annual disclosures will be effective for the Company for fiscal year 2024 and for interim disclosures will be effective for the Company for fiscal year 2025. The guidance must be applied retrospectively and early adoption is permitted. The Company does not expect to early adopt this guidance and does not expect these changes to have an impact on the Company’s consolidated financial statements other than disclosure requirements.

In December 2023, the FASB issued new accounting guidance related to income tax disclosures. This guidance requires entities to disclose specific categories in its annual rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This guidance also requires additional annual disclosures for income taxes paid and requires disaggregation of income before tax, between domestic and foreign, and income tax expense, between federal, state and foreign. This guidance also eliminates several current disclosure requirements related to the nature and estimate of the range of the reasonably possible change in the unrecognized tax benefits balance in the next 12 months and making a statement that an estimate of the range cannot be made and disclosing the cumulative amount of each type of temporary difference when a deferred tax liability is not recognized because of the exceptions to comprehensive recognition of deferred taxes related to subsidiaries and corporate joint ventures. This new guidance will be effective for the Company for fiscal year 2025 and must be applied on a prospective basis with retrospective application permitted. Early adoption of this guidance is also permitted. The Company does not expect to early adopt this guidance and does not expect these changes to have an impact on the Company’s consolidated financial statements other than disclosure requirements.

Asset Retirement Obligations

The Company maintains reserves where a legal obligation exists to perform an asset retirement activity and the fair value of the liability can be reasonably estimated. These asset retirement obligations (AROs) include liabilities where the timing and (or) method of settlement may be conditional on a future event, that may or may not be within the control of the entity. At December 31, 2023, the Company had recognized AROs of $18.3 million related to landfill closures, decommissioning costs, facility leases and conditional AROs associated with manufacturing activities using what may be characterized as potentially hazardous materials.

Estimates of AROs are evaluated annually in the fourth quarter, or more frequently if material new information becomes known. Accounting for asset retirement obligations requires significant estimation and in certain cases, the Company has determined that an ARO exists, but the amount of the obligation is not reasonably estimable. The Company may determine that additional AROs are required to be recognized as new information becomes available.

Derivative Financial Instruments and Hedging

As part of its risk management strategy, the Company, from time-to-time, utilizes derivative financial instruments to manage its exposure to changes in raw material prices, energy costs, foreign currencies, and interest rates. In accordance with applicable accounting standards, the Company accounts for most of these contracts as hedges.

The Company sometimes uses futures and swap contracts to manage exposure to changes in prices for forecasted purchases of raw materials, such as nickel, and natural gas. Under these contracts, which are generally accounted for as cash flow hedges, the price of the item being hedged is fixed at the time that the contract is entered into and the Company is obligated to make or receive a payment equal to the net change between this fixed price and the market price at the date the contract matures.

The majority of ATI’s products are sold utilizing raw material surcharges and index mechanisms. However, as of December 31, 2023, the Company had entered into financial hedging arrangements primarily at the request of its customers, related to firm orders, for an aggregate notional amount of approximately 4 million pounds of nickel with hedge dates through fiscal year 2024. The aggregate notional amount hedged is approximately 6% of a single year’s estimated nickel raw material purchase requirements. These derivative instruments are used to hedge the variability of a selling price that is based on the London Metals Exchange (LME) index for nickel, as well as to hedge the variability of the purchase cost of nickel based on this LME index. Any gain or loss associated with these hedging arrangements is included in sales or cost of sales, depending on whether the underlying risk being hedged was the variable selling price or the variable raw material cost, respectively.

At December 31, 2023, the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2023, the company hedged approximately 75% of the Company’s annual forecasted domestic requirements for natural gas for fiscal year 2024 and approximately 35% for fiscal year 2025.

While the majority of the Company’s direct export sales are transacted in U.S. dollars, foreign currency exchange contracts are used, from time-to-time, to limit transactional exposure to changes in currency exchange rates for those transactions denominated in a non-U.S. currency. The Company sometimes purchases foreign currency forward contracts that permit it to sell specified amounts of foreign currencies expected to be received from its export sales for pre-established U.S. dollar amounts at specified dates. In addition, the Company may also hedge forecasted capital expenditures and designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. At December 31, 2023, the Company had no significant outstanding foreign currency forward contracts.

The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. The Company has a $50 million floating-for-fixed interest rate swap that matures in June 2024 which converts a portion of the ABL Term Loan to a 4.21% fixed rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its ABL Term Loan borrowings. The ineffective portion at hedge inception, determined from the fair value of the swap immediately prior to amendment in July 2019, was amortized to interest expense over the initial ABL Term Loan swap maturity date of January 12, 2021.

There are no credit risk-related contingent features in the Company’s derivative contracts, and the contracts contained no provisions under which the Company has posted, or would be required to post, collateral. The counterparties to the Company’s derivative contracts were substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible.

For derivative financial instruments that are designated as cash flow hedges, the gain or loss on the derivative is reported as a component of other comprehensive income (OCI) and reclassified into earnings in the same period or periods during which the

hedged item affects earnings. For derivative financial instruments that are designated as fair value hedges, changes in the fair value of these derivatives are recognized in current period results. There were no outstanding fair value hedges as of December 31, 2023 or January 1, 2023. The cash flow impact for all derivative financial instruments is reported in cash flows provided by operating activities on the consolidated statement of cash flows. The Company did not use net investment hedges for the periods presented.

Pension Plans and Other Postretirement Benefits

The Company has defined contribution retirement plans or defined benefit pension plans covering substantially all employees. Company contributions to defined contribution retirement plans are generally based on a percentage of eligible pay or based on hours worked. Benefits under the defined benefit pension plans are generally based on years of service and/or final average pay. The Company also sponsors several postretirement plans covering certain collectively-bargained salaried and hourly employees. The plans provide health care and life insurance benefits for eligible retirees. In most retiree health care plans, Company contributions towards premiums are capped based on the cost as of a certain date, thereby creating a defined contribution.