X0609 4 2026-09-09 1 0001828185 Barinthus Biotherapeutics plc. BRNS 0001851633 Hammacher Alex false C/O BARINTHUS BIOTHERAPEUTICS PLC 20400 CENTURY BOULEVARD GERMANTOWN MD 20874 1 0 0 0 0 Ordinary Shares 2026-09-09 4 D 0 3000 D 0 D Share Option (Right to Buy) 17.00 2026-09-09 4 D 0 34328 0.00 D 2031-05-01 Ordinary Shares 34328 0 D Share Option (Right to Buy) 4.27 2026-09-09 4 D 0 18604 0.00 D 2032-06-15 Ordinary Shares 18604 0 D Share Option (Right to Buy) 2.27 2026-09-09 4 D 0 19197 0.00 D 2033-05-11 Ordinary Shares 19197 0 D Share Option (Right to Buy) 2.34 2026-09-09 4 D 0 19516 0.00 D 2034-05-10 Ordinary Shares 19516 0 D Share Option (Right to Buy) 1.00 2026-09-09 4 D 0 20174 0.00 D 2035-06-10 Ordinary Shares 20174 0 D The Ordinary Shares may be represented by American Depositary Shares ("ADSs" and together with the Ordinary Shares, the "Shares"), each of which currently represents one Ordinary Share. This Form 4 reports securities transacted in connection with the Agreement and Plan of Merger, dated September 29, 2025, as amended (the "Merger Agreement") by and among the Issuer, Beacon Topco, Inc. ("Topco"), a Delaware corporation and a direct wholly owned subsidiary of the Issuer, Cdog Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Topco, and Clywedog Therapeutics, Inc., a Delaware corporation. On September 9, 2026 (the "Effective Time"), in connection with the effectiveness of the scheme of arrangement under Part 26 of the United Kingdom Companies Act 2006 (the "Scheme") contemplated by the Merger Agreement, Topco acquired the entire issued share capital of the Issuer, resulting in the Issuer becoming a direct wholly owned subsidiary of Topco. Pursuant to the Merger Agreement and in connection with the effectiveness of the Scheme, at the Effective Time, each Share of the Issuer was converted into the right to receive 0.111 shares of common stock, $0.0001 par value per share, of Topco (the "Topco Common Stock"). Pursuant to the Merger Agreement, at the Effective Time, each option to acquire Shares under the Issuer's equity plans that was outstanding as of immediately prior to the Effective Time ceased to represent a right to acquire Shares of the Issuer, and was converted into an option to acquire shares of Topco Common Stock and assumed by Topco on the same terms and conditions (including applicable vesting and exercisability conditions) as were applicable to such option immediately prior to the Effective Time. /s/ William Enright, Attorney-in-Fact 2026-09-09