UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of report (Date of earliest event reported): March 21, 2025

Concord Acquisition Corp II

(Exact name of registrant as specified in its charter)

(212) 883-4330
(Registrant’s telephone number, including area code)

Not Applicable
(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨     Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨     Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨     Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨     Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company   x

If an emerging growth company, indicate 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.  ¨

On March 21, 2025, Concord Acquisition Corp II (the “Company”) was notified by Marcum LLP (“Marcum”) that Marcum resigned as the independent registered accounting firm of the Company. On November 1, 2024, CBIZ CPAs P.C. acquired the attest business of Marcum. On March 21, 2025, upon Marcum’s resignation as auditors of the Company and with the approval of the Company’s Board of Directors, CBIZ CPAs P.C. was engaged as the Company’s independent registered public accounting firm.

The reports of Marcum regarding the Company’s consolidated financial statements for the fiscal years ended December 31, 2024 and 2023 did not contain any adverse opinion or disclaimer of opinion and were not qualified or modified as to uncertainty, audit scope, or accounting principles, except that the reports included an explanatory paragraph indicating that there was substantial doubt about the Company’s ability to continue as a going concern.

During the fiscal years ended December 31, 2024 and December 31, 2023, and through March 21, 2025, the date of Marcum’s resignation, there were (a) no disagreements (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) with Marcum on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedures, which disagreements, if not resolved to the satisfaction of Marcum, would have caused Marcum to make reference to such disagreement in its report and (b) no “reportable events” (as defined in Item 304(a)(1)(v) of Regulation S-K and the related instructions), except for the material weakness in the Company’s internal control over financial reporting related to the accounting for complex financial instruments, as reported in the Company’s Annual Reports on Form 10-K for the years ended December 31, 2024 and December 31, 2023.

During the fiscal years ended December 31, 2024 and December 31, 2023, and through March 21, 2025, the date of Marcum’s resignation, neither the Company nor anyone on the Company’s behalf consulted with CBIZ CPAs P.C. regarding (i) the application of accounting principles to a specific completed or contemplated transaction or regarding the type of audit opinions that might be rendered by CBIZ CPAs P.C. on the Company’s consolidated financial statements, and CBIZ CPAs P.C. did not provide any written or oral advice that was an important factor considered by the Company in reaching a decision as to any such accounting, auditing, or financial reporting issue or (ii) any matter that was either the subject of a disagreement (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions), as that term is described in Item 304(a)(1)(iv) of Regulation S-K, or a reportable event, as that term is defined in Item 304(a)(1)(v) of Regulation S-K.

The Company provided Marcum with a copy of this Current Report on Form 8-K prior to its filing with the U.S. Securities and Exchange Commission (the “SEC”) and requested that Marcum furnish the Company with a letter addressed to the SEC, pursuant to Item 304(a)(3) of Regulation S-K, stating whether it agrees with the above statements and, if it does not agree, the respects in which it does not agree. A copy of the letter, dated March 24, 2025, is filed as Exhibit 16.1 (which is incorporated by reference herein) to this Current Report on Form 8-K.

(d) Exhibits.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: March 24, 2025