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): September 22, 2026

BEACON TOPCO, INC.

(Exact name of registrant as specified in its charter)

20400 Century Boulevard, Suite 210

Germantown, MD 20874

United States of America

(Address of principal executive offices, including zip code)

(443) 917-0966

(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 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 (§ 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. ¨

Amendment to the Merger Agreement

As previously disclosed, on September 29, 2025, Beacon Topco, Inc., a Delaware corporation (“Topco”), entered into an Agreement and Plan of Merger by and among Topco, Barinthus Biotherapeutics plc, a direct wholly owned subsidiary of Topco (“Beacon”), Cdog Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Topco (“Merger Sub”), and Clywedog Therapeutics, Inc., a Delaware corporation (“Clywedog”). On February 22, 2026, Topco, Beacon, Merger Sub and Clywedog entered into an Amendment to the Agreement and Plan of Merger (as amended, the “Original Merger Agreement”).

Also as previously disclosed and pursuant to the terms of the Original Merger Agreement, on September 9, 2026, Topco acquired the entire issued and to be issued share capital of Beacon pursuant to a scheme of arrangement which was approved by the High Court of Justice of England and Wales (the “Court”) on September 1, 2026 (the “Scheme of Arrangement” and such transaction, the “Scheme Transaction”). The Original Merger Agreement also provides that Merger Sub will merge with and into Clywedog, with Clywedog continuing as the surviving corporation and a direct wholly owned subsidiary of Topco in accordance with the Delaware General Corporations Law (together with the Scheme Transaction, the “Combinations”).

On September 22, 2026, Topco, Beacon, Merger Sub and Clywedog entered into the Second Amendment to the Agreement and Plan of Merger (the “Second Merger Agreement Amendment”). Pursuant to the Second Merger Agreement Amendment, (i) the closing timeline as set forth in Section 2.3 of the Original Merger Agreement was amended and restated in its entirety such that the closing will occur on October 31, 2026 (or earlier if mutually agreed by the parties), and (ii) the definition of “End Date” as set forth in Section 10.1(b) of the Original Merger Agreement was amended and restated in its entirety to be October 31, 2026. The foregoing description of the Second Merger Agreement Amendment is subject to and qualified in its entirety by reference to the full text of the Second Merger Agreement Amendment, a copy of which is included as Exhibit 2.1 hereto, and the terms of which are incorporated herein by reference.

On September 24, 2026, Topco and Clywedog issued a joint press release titled “Clywedog Therapeutics Announces Final Results from a Phase 1b Study of Balomenib in Type 2 Diabetes Patients, Showing Glycemic Improvement Sustained for Three Months After a Three-Week Course of Treatment.” The full text of the press release is filed as Exhibit 99.1 to this Current Report on Form 8-K and incorporated herein by reference.

Forward Looking Statements

This Current Report on Form 8-K contains forward-looking statements, within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, which can generally be identified as such by use of the words “expect,” “will,” and similar expressions, although not all forward-looking statements contain these identifying words. Any forward-looking statements in this Current Report on Form 8-K are based on management’s current expectations and beliefs and are subject to numerous risks, uncertainties and important factors that may cause actual events or results to differ materially from those expressed or implied by any forward-looking statements contained in this Current Report on Form 8-K, including, without limitation, risks and uncertainties related to the success, cost and timing of the Company’s pipeline development activities and planned and ongoing clinical trials, the Company’s ability to execute on its strategy, regulatory developments, the risk that the Company may not achieve the anticipated benefits of its pipeline prioritization and corporate restructuring, the Company’s ability to fund its operations and access capital, the Company’s preliminary estimates of its cash and cash equivalents, including the risk that final financial results may differ materially from the Company’s preliminary estimates, and other risks identified in the Company’s filings with the Securities and Exchange Commission (the “SEC”), including its Quarterly Reports on Form 10-Q and subsequent filings with the SEC. The Company cautions you not to place undue reliance on any forward-looking statements, which speak only as of the date they are made. The Company expressly disclaims any obligation to publicly update or revise any such statements to reflect any change in expectations or in events, conditions or circumstances on which any such statements may be based, or that may affect the likelihood that actual results will differ from those set forth in the forward-looking statements.

(d) Exhibits.

SIGNATURES

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.

ATTACHMENTS / EXHIBITS

EXHIBIT 2.1

EXHIBIT 99.1

XBRL TAXONOMY EXTENSION SCHEMA

XBRL TAXONOMY EXTENSION LABEL LINKBASE

XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE

IDEA: R1.htm

IDEA: FilingSummary.xml

IDEA: MetaLinks.json

IDEA: tm2625953d2_8k_htm.xml