UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

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

Date of Report (Date of earliest event reported): September 30, 2025

Chain Bridge I

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (202) 656-4257

(Former name or former address, if changed since last report)

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

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 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company  ☒

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.  ☐

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

On September 30, 2025, the Company issued an unsecured, non-interest bearing promissory note (the “Note”) to C/M Capital Master Fund LP (the “Lender”) in the aggregate principal amount of $1,250,000, for an aggregate purchase price of $1,000,000.

The Note is due and payable in full on the maturity date, June 30, 2026 (the “Maturity Date”); provided that, upon the occurrence of an Event of Default (as defined below), the outstanding principal and any other amounts outstanding under the Note will become due and payable without demand. The Note may be prepaid at any time without penalty. All payments due under the Note rank junior to certain existing indebtedness of the Company and senior to all other indebtedness of the Company and its subsidiaries. The proceeds of the Note will be used to pay for certain fees and expenses incurred in connection with the Company’s initial business combination and for other general corporate purposes.

The Note includes customary representations, warranties, covenants and events of default (each, an “Event of Default”), including, among others, (i) certain events of bankruptcy, insolvency or reorganization; (ii) breach of certain representations, warranties, covenants or other terms of the Note that remains uncured for five (5) business days, and (iii) failure to establish and authorize a new series of preferred shares of the Company by November 15, 2025 (the “New Preferred Shares”). The Lender has the right to exchange all or any portion of the Note for New Preferred Shares, on terms to be mutually agreed upon by the Company and the Lender.

The foregoing description of the Note is not complete and is qualified in its entirety by reference to the full text of the Note, a copy of which is filed herewith as Exhibit 4.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(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.

Dated: October 6, 2025

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