CONSTELLIUM SE

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

For the quarterly period ended September 30, 2025

OR

For the transition period from _________ to __________

Commission file number:001-35931

Constellium SE

(Exact name of registrant as specified in its charter)

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months, (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.☑ Yes ☐ No

Indicate by check mark whether the registrant submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).☑ Yes ☐ No

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company", and "emerging growth company" in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicated by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). ☐ Yes☑ No

The number of outstanding ordinary shares of the registrant on September 30, 2025, was 137,801,779 shares.

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Explanatory Note

Constellium SE (“Constellium SE” or “the Company”, and when referred to together with its subsidiaries, “the Group” or “Constellium”), is a corporation organized under the laws of France. As of June 30, 2025, Constellium SE no longer qualified as a Foreign Private Issuer, as determined by Rule 3b-4 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Beginning in 2025, Constellium SE begun voluntarily electing to file annual reports on Form 10-K and quarterly reports on Form 10-Q with the Securities and Exchange Commission (“SEC”). Beginning on January 1, 2026, Constellium will continue to file annual reports on Form 10-K and quarterly reports on Form 10-Q and will also file all other required U.S. domestic forms with the SEC, including proxy materials pertaining to meetings of its shareholders, and its officers, directors and 10% shareholders will be subject to beneficial ownership reporting under Section 16 of the Exchange Act.

Constellium SE’s I.R.S. Employer Identification Number is: 98-0667516. The Group’s U.S. assets are held by Constellium US Holdings I, LLC, a wholly owned subsidiary of Constellium SE. The I.R.S. Employer Identification Number of Constellium US Holdings I, LLC is: 27-4126819.

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