10-Q/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

(Amendment No. 1)

FORM 10-Q/A

(MARK ONE)

x QUARTERLY REPORT PURSUANT TO SECTION13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarter ended September 30, 2025

¨ TRANSITION REPORT PURSUANT TO SECTION13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                 to

Commission file number: 001-42252

TERRESTRIAL ENERGY INC.

(Exact Name of Registrant as Specified in Its Charter)

(646) 687-8212

(Issuer’s telephone number)

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

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 x No ¨

Indicate by check mark whether the registrant has 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 x 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 an 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, 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. ¨

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

As of November 14, 2025, there were 81,771,423

shares of the registrant’s common stock, $0.0001 par value, outstanding. In addition, as of November 14, 2025, there were 24,011,029 shares of the registrant’s common stock issuable upon exchange of outstanding exchangeable shares of a subsidiary, which are convertible into shares of common stock of the registrant on a one for one basis.

EXPLANATORY NOTE

This Amendment No. 1 on Form 10-Q/A (the “Amendment”) is being filed solely (i) to correct the number of shares of common stock outstanding on the cover page of the registrant’s Form 10-Q for the period ended September 30, 2025 (the “Original Filing”) filed with the Securities and Exchange Commission (the “Commission”) on November 14, 2025 and (ii) to correct the cover page check boxes erroneously indicating that the registrant was a shell company as of Original Filing and had not filed all reports required to be filed during the preceding 12 months. As previously reported in the Form 8-K filed by the registrant on November 3, 2025, the registrant ceased being a shell company upon the completion of the Merger as described in such Form 8-K. No other changes have been made to the Original Filing, whether to update the Original Filing to reflect events occurring subsequent to the filing of the Original Filing or otherwise.

As required by Rule 12b-15 of the Securities Exchange Act of 1934, as amended, this Form 10-Q/A contains new certifications by the registrant’s principal executive officer and principal financial officer under Section 302 of the Sarbanes-Oxley Act of 2002, which are being filed as exhibits to this Form 10-Q/A. Because this Form 10-Q/A includes no financial statements, the registrant is not including certifications pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.

Item6. Exhibits

The following exhibits are filed as part of, or incorporated by reference into, this Quarterly Report on Form 10-Q.

PART III - SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this Amendment No. 1 to be signed on its behalf by the undersigned, thereunto duly authorized.

Exhibit 31.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER

PURSUANT TO RULE 13A-14(A) UNDER THE SECURITIESEXCHANGE ACT OF 1934,

AS ADOPTED PURSUANT TO SECTION 302 OF THE SARBANES-OXLEYACT OF 2002

I, Simon Irish, certify that:

Date: November 20, 2025

Exhibit 31.2

CERTIFICATION OF CHIEF FINANCIAL OFFICER

PURSUANT TO RULE 13A-14(A) UNDER THE SECURITIESEXCHANGE ACT OF 1934,

AS ADOPTED PURSUANT TO SECTION 302 OF THE SARBANES-OXLEYACT OF 2002

I, Brian Thrasher, certify that:

Date: November 20, 2025