BUSINESS AND SUMMARY OF ACCOUNTING POLICIES	9 Months Ended
Sep. 30, 2026
Accounting Policies [Abstract]
BUSINESS AND SUMMARY OF ACCOUNTING POLICIES	NOTE 1 - BUSINESS AND SUMMARY OF ACCOUNTING POLICIES Constellium is a global leader in the development, manufacture and sale of a broad range of high value-added specialty rolled and extruded aluminum products to the aerospace, space, defense, packaging, automotive, commercial transportation and general industrial end-markets. At September 30, 2026, the Group operated 23 manufacturing facilities, 3 R&D centers and 3 administrative centers. The Group has approximately 11,500 employees. Unless the context indicates otherwise, when we refer to “we,” “our,” “us,” “Constellium,” the “Group” and the “Company” in this document, we are referring to Constellium SE and its subsidiaries, and when we refer to “Constellium SE”, we are referring to Constellium SE on a standalone basis. Basis of presentation and principles of consolidation The accompanying unaudited interim condensed consolidated financial statements include the accounts of Constellium SE and its controlled subsidiaries. All intercompany transactions and balances are eliminated. The accompanying unaudited interim condensed consolidated financial statements have been prepared by Constellium in accordance with U.S. generally accepted accounting principles (“GAAP”) and the rules and regulations of the Securities and Exchange Commission (“SEC”) applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair statement of its financial position at September 30, 2026, results of operations and cash flows for the three-month and nine-month periods ended September 30, 2026 and 2025 have been included. The accompanying unaudited interim condensed consolidated financial statements should be read in conjunction with the Group’s audited consolidated financial statements and accompanying notes in its Annual Report on Form 10-K for the year ended December 31, 2025 (“Annual Report”). The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2026 fiscal year. Use of estimates and assumptions The preparation of the Group’s consolidated financial statements in accordance with U.S. GAAP requires management to make judgments, estimates and assumptions that affect the reported amounts of revenues, expenses, assets and liabilities, and the accompanying disclosures, and the disclosure of contingent liabilities. The principal areas of judgment relate to: (1) impairment of assets; (2) actuarial assumptions related to pension and other postretirement benefit plans; (3) tax uncertainties and valuation allowances; and (4) assessment of loss contingencies, including environmental and litigation liabilities. These judgments, estimates and assumptions are based on management’s best knowledge of the relevant facts and circumstances, giving consideration to previous experience. Future events and their effects cannot be predicted with certainty, and, accordingly, our accounting estimates require the exercise of judgment. The accounting estimates used in the preparation of our consolidated financial statements may change as new events occur, more experience is acquired, additional information is obtained, and our operating environment changes. The Group continuously reviews its significant assumptions and estimates in light of the uncertainty associated with the global geopolitical and macroeconomic conditions and their potential direct and indirect impacts on its business and its financial statements. There can be no guarantee that our assumptions will materialize or that actual results will not differ materially from estimates. Recently adopted and recently issued accounting guidance The Group plans to adopt new standards, amendments and interpretations, as disclosed in our Annual Report, on their required effective dates and does not expect any material impact on its financial position, results of operations and cash flows as a result of their adoption.

BUSINESS AND SUMMARY OF ACCOUNTING POLICIES

9 Months Ended

Sep. 30, 2026

BUSINESS AND SUMMARY OF ACCOUNTING POLICIES

NOTE 1 - BUSINESS AND SUMMARY OF ACCOUNTING POLICIES

Constellium is a global leader in the development, manufacture and sale of a broad range of high value-added specialty

rolled and extruded aluminum products to the aerospace, space, defense, packaging, automotive, commercial transportation and

general industrial end-markets. At September 30, 2026, the Group operated 23 manufacturing facilities, 3 R&D centers and 3

administrative centers. The Group has approximately 11,500 employees.

Unless the context indicates otherwise, when we refer to “we,” “our,” “us,” “Constellium,” the “Group” and the

“Company” in this document, we are referring to Constellium SE and its subsidiaries, and when we refer to “Constellium SE”,

we are referring to Constellium SE on a standalone basis.

Basis of presentation and principles of consolidation

The accompanying unaudited interim condensed consolidated financial statements include the accounts of

Constellium SE and its controlled subsidiaries. All intercompany transactions and balances are eliminated.

The accompanying unaudited interim condensed consolidated financial statements have been prepared by Constellium in

accordance with U.S. generally accepted accounting principles (“GAAP”) and the rules and regulations of the Securities and

Exchange Commission (“SEC”) applicable for interim periods and, therefore, do not include all information and footnotes

required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal

recurring adjustments) considered necessary for a fair statement of its financial position at September 30, 2026, results of

operations and cash flows for the three-month and nine-month periods ended September 30, 2026 and 2025 have been included.

The accompanying unaudited interim condensed consolidated financial statements should be read in conjunction with the

Group’s audited consolidated financial statements and accompanying notes in its Annual Report on Form 10-K for the year

ended December 31, 2025 (“Annual Report”). The results of operations for our interim periods are not necessarily indicative of

the results of operations that may be achieved for the entire 2026 fiscal year.

Use of estimates and assumptions

The preparation of the Group’s consolidated financial statements in accordance with U.S. GAAP requires management to

make judgments, estimates and assumptions that affect the reported amounts of revenues, expenses, assets and liabilities, and

the accompanying disclosures, and the disclosure of contingent liabilities. The principal areas of judgment relate to:

(1) impairment of assets; (2) actuarial assumptions related to pension and other postretirement benefit plans; (3) tax

uncertainties and valuation allowances; and (4) assessment of loss contingencies, including environmental and litigation

liabilities. These judgments, estimates and assumptions are based on management’s best knowledge of the relevant facts and

circumstances, giving consideration to previous experience. Future events and their effects cannot be predicted with certainty,

and, accordingly, our accounting estimates require the exercise of judgment. The accounting estimates used in the preparation

of our consolidated financial statements may change as new events occur, more experience is acquired, additional information

is obtained, and our operating environment changes. The Group continuously reviews its significant assumptions and estimates

in light of the uncertainty associated with the global geopolitical and macroeconomic conditions and their potential direct and

indirect impacts on its business and its financial statements. There can be no guarantee that our assumptions will materialize or

that actual results will not differ materially from estimates.

Recently adopted and recently issued accounting guidance

The Group plans to adopt new standards, amendments and interpretations, as disclosed in our Annual Report, on their

required effective dates and does not expect any material impact on its financial position, results of operations and cash flows as

a result of their adoption.