UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

(MARK ONE)

For the fiscal year ended December 31, 2025

For the transition period from to

Commission file number: 001-42199

ADAGIO MEDICAL HOLDINGS, INC.

(Exact Name of Registrant as Specified in Its Charter)

(949) 348-1188

(Issuer’s telephone number, including area code)

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

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ¨ No x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ¨ No x

Check whether the issuer (1) filed all reports required to be filed by Section 13 or 15(d) of the Exchange Act during the past 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 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 has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act by the registered public accounting firm that prepared or issued its audit report. ¨

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. ¨

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ¨

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 June 30, 2025, the aggregate market value of the common stock of the registrant held by non-affiliates was: $7.0 million.

As of March 23, 2026, there were 22,210,459 shares of common stock, $0.0001 par value, issued and outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive Proxy Statement to be filed in connection with the registrant’s 2026 annual general meeting of shareholders (“2026 Proxy Statement”) are incorporated by reference into Part III of this Form 10 K where indicated. The 2026 Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.

EXPLANATORY NOTE

Adagio Medical Holdings, Inc. is filing this Amendment No. 1 on Form 10-K/A (the “Amendment”) to amend its original Annual Report on Form 10-K for the period ended December 31, 2025 (the “Original Form 10-K”), originally filed with the Securities and Exchange Commission (the “SEC”) on March 27, 2026, for the sole purpose of including revised Exhibits 31.1 and 31.2, which replace the previously filed versions of those exhibits, to correct an inadvertent omission of certain language from paragraph 4 of the Exhibit 31.1 and Exhibit 31.2 certifications filed with the Original Form 10-K.

This Amendment contains only the Cover Page to this Amendment, this Explanatory Note, Item 15, the Signature Page, and the certifications attached to this Amendment as Exhibits 31.1 and 31.2. No other changes have been made to the Original Form 10-K. This Amendment speaks as of the original filing date of the Original Form 10-K, does not reflect events that may have occurred subsequent to the original filing date, and does not modify or update in any way disclosures made in the Original Form 10-K.

Accordingly, this Amendment should be read in conjunction with the Original Form 10-K and our other filings with the SEC. The filing of this Amendment is not an admission that the Original Form 10-K, when filed, included any untrue statement of a material fact or omitted to state a material fact necessary to make a statement not misleading.

PART IV

(b) Exhibits.

The following exhibits are filed as part of, or incorporated by reference into, this Amendment.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.