X0202 SCHEDULE 13D/A 0001581835 XXXXXXXX LIVE 6 Ordinary Shares, nominal value EUR0.02 per share 05/26/2026 false 0001563411 F21107101 Constellium SE

300 East Lombard Street Suite 1710 Baltimore MD 21202

Sophie Paquin 33 1 53 89 55 73 6-8, boulevard Haussmann Paris I0 75009 John Partigan Lloyd Spencer 202-585-8000 Nixon Peabody LLP 799 9th Street NW, Suite 500 Washington DC 20001 Y Caisse des Depots (CDC) OO N I0 0.00 8403903.00 0.00 8403903.00 8403903.00 N 6.2 OO 0001581835 N Bpifrance Participations S.A. OO N I0 0.00 8403903.00 0.00 8403903.00 8403903.00 N 6.2 OO 0001731118 N Bpifrance S.A. OO N I0 0.00 8403903.00 0.00 8403903.00 8403903.00 N 6.2 OO 0001731121 N EPIC Bpifrance OO N I0 0.00 8403903.00 0.00 8403903.00 8403903.00 N 6.2 OO Ordinary Shares, nominal value EUR0.02 per share Constellium SE 300 East Lombard Street Suite 1710 Baltimore MD 21202 Introductory Statement: This Amendment No. 6 (this "Amendment") is being filed by Bpifrance Participations S.A., a societe anonyme incorporated under the laws of the Republic of France ("Bpifrance Participations"), EPIC Bpifrance, a French public institution of industrial and commercial nature ("EPIC"), Bpifrance S.A., a societe anonyme incorporated under the laws of the Republic of France ("Bpifrance"), and Caisse des depots, a French special public entity (etablissement special) ("CDC") (collectively, the "Reporting Persons") pursuant to Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). This Amendment relates to the Ordinary Shares, nominal value Euro 0.02 per share (the "Ordinary Shares") of Constellium SE (the "Issuer"). This Amendment amends the Statement on Schedule 13D relating to Ordinary Shares of the Issuer filed with the Securities and Exchange Commission (the "SEC") on June 10, 2013, as amended by Amendment No. 1 filed with the SEC on July 25, 2013, Amendment No. 2 filed with the SEC on September 7, 2017, Amendment No. 3 filed with the SEC on November 8, 2017, Amendment No. 4 filed with the SEC on August 10, 2023, and Amendment No. 5 filed with the SEC on June 6, 2024 (as amended, the "Schedule 13D"). Except as specifically provided herein, this Amendment does not modify any of the information previously reported in the Schedule 13D. Capitalized terms used in this Amendment but not otherwise defined herein have the meanings given to them in the Schedule 13D. Information concerning the executive officers and directors of Bpifrance Participations, EPIC, Bpifrance, and CDC required to be disclosed in response to Item 2 and General Instruction C to Schedule 13D is provided in Exhibit 99.4 to this Amendment and incorporated herein by reference. None of the Reporting Persons, nor, to the best of their knowledge, any of the persons referred to in Exhibit 99.4 has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations and similar misdemeanors). None of the Reporting Persons, nor, to the best of their knowledge, any of the persons referred to in Exhibit 99.4 has, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree, or final order enjoining future violations of, or prohibiting or mandating activities subject to, Federal or state securities laws or finding any violation with respect to such laws. Item 4 is hereby amended and supplemented as follows: On May 26, 2026, Bpifrance Participations sold 4,190,000 Ordinary Shares by two block trades each at $33.89 per share. All of the Ordinary Shares that are held of record by the Reporting Persons as reported herein were acquired for investment purposes. The Reporting Persons retain the right to change their investment intent, from time to time to acquire additional Ordinary Shares or other securities of the Issuer, or to sell or otherwise dispose of all or part of the Ordinary Shares or other securities of the Issuer, if any, beneficially owned by them, in any manner permitted by law. The Reporting Persons may engage from time to time in ordinary course transactions with financial institutions with respect to the securities described herein. Except as set forth above, none of the Reporting Persons currently has any plans or proposals which would be related to or would result in any of the matters described in Items 4(a)-(j) of the Instructions to Schedule 13D. However, as part of the ongoing evaluation of investment and investment alternatives, the Reporting Persons may consider such matters and, subject to applicable law, may formulate a plan with respect to such matters, and, from time to time, may hold discussions with or make formal proposals to management or the board of directors of the Issuer or other third parties regarding such matters. Item 5(a) of the Schedule 13D is hereby amended and supplemented as follows: As of the date hereof, Bpifrance Participations holds directly 8,403,903 Ordinary Shares, which represents approximately 6.2% of the Issuer's Ordinary Shares. As of the date hereof, none of Bpifrance S.A., CDC, or EPIC holds any Ordinary Shares directly. Bpifrance S.A. may be deemed to be the beneficial owner of 8,403,903 Ordinary Shares, indirectly through its sole ownership of Bpifrance Participations. CDC and EPIC may be deemed to be the beneficial owners of 8,403,903 Ordinary Shares, indirectly through their joint ownership and control of Bpifrance S.A. The ownership percentages are calculated based on 136,150,450 Ordinary Shares outstanding as of April 1, 2026, as reported by the Issuer in its definitive proxy statement filed with the SEC on April 10, 2026. Item 5(b) of the Schedule 13D is hereby amended and supplemented as follows: See the information contained on the cover pages of this Amendment, which is incorporated herein by reference. Item 5(c) of the Schedule 13D is hereby amended and supplemented as follows: The information set forth in Item 4 is hereby incorporated by reference to this Item 5(c). Except as disclosed in this Amendment, there have been no reportable transactions with respect to the Ordinary Shares of the Issuer within the last 60 days by the Reporting Persons, or, to the best of their knowledge, any of the persons referred to in Exhibit 99.4. Item 6 of the Schedule 13D is hereby amended and supplemented as follows: In connection with the block sales described above in Item 4, Bpifrance Participations has agreed, for a period of 60 days, to not offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend or otherwise transfer or dispose of, directly or indirectly, any Ordinary Shares of the Issuer or any securities convertible into or exercisable or exchangeable for Ordinary Shares of the Issuer subject to certain exceptions and approvals. EX 99.1: Power of Attorney -- CDC (incorporated by reference to Exhibit 1 to Amendment No. 2 to the Schedule 13D filed by Bpifrance Participations on September 7, 2017). EX 99.2: Power of Attorney -- Bpifrance S.A (incorporated by reference to Exhibit 2 to Amendment No. 2 to the Schedule 13D filed by Bpifrance Participations on September 7, 2017). EX 99.3: Power of Attorney -- EPIC and Bpifrance Participations (incorporated by reference to Exhibit 3 to Amendment No. 1 to the Schedule 13G filed by Bpifrance Participations on February 14, 2017). EX 99.4: Information with respect to the Directors and Executive Officers of the Reporting Persons. Caisse des Depots (CDC) /s/ Laurence Giraudon 05/28/2026 Bpifrance Participations S.A. /s/ Sophie Paquin 05/28/2026 Bpifrance S.A. /s/ Boubakar Dione 05/28/2026 EPIC Bpifrance /s/ Sophie Paquin 05/28/2026