Posting of Circular and Notice of General Meeting

20 October 2026

4basebio PLC

(“4basebio” or the “Company”)

Posting of Circular and Notice of General Meeting

CAMBRIDGE, UK – 20 October 2026 - 4basebio PLC (AIM: 4BB), a specialist in synthetic DNA manufacturing for next-generation genomic medicines and advanced therapies, is pleased to provide a further update in relation to the proposed Capital Raise announced on 15 October 2026.

The Company has today posted to shareholders a circular convening the General Meeting required in connection with the Capital Raise (the “Circular”), at which shareholders will be asked to consider, and if thought fit, approve, the Resolutions set out in the Circular. Completion of the Capital Raise is conditional on approval of the Resolutions.

The General Meeting will be held at 10.00 a.m. on 6 November 2026 at the offices of Cooley (UK) LLP, 22 Bishopsgate, London EC2N 4BQ. A copy of the Circular is also available to view on the Company’s website, www.4basebio.com/investors.

Please note that shareholders intending to attend the General Meeting in person will need a QR code, displayed on a smartphone or similar device, to access the meeting venue. A QR code can be obtained in advance by emailing [email protected] with your full name, full address and email address, or on arrival for shareholders who have not done so in advance.

The Directors are of the opinion that the proposed Capital Raise is in the best interests of the Company and its shareholders as a whole, and unanimously recommend that shareholders vote in favour of the Resolutions, as they intend to do in respect of their own beneficial holdings.

Capitalised terms in this announcement shall have the same meaning as set out in the Circular.

Enquiries

4basebio PLC+44 (0)12 2396 7943Dr. Amy Walker – Chief Executive OfficerRichard Bungay – Chief Financial Officer

RBC Capital Markets (Global Co-ordinator, Joint Bookrunner and Joint Corporate Broker)T: +44 (0)20 7653 4000Kathryn Deegan – ECM Max Avison – ECM SyndicateSandrine Cailleteau – Healthcare Advisory

Cavendish Capital Markets Limited (Joint Bookrunner and Joint Corporate Broker)T: +44 (0)20 7220 0500Geoff Nash, Andrea Callaghan – Corporate FinanceNigel Birks – Healthcare Specialist Sales

Cairn Financial Advisers LLP (Nominated Adviser)T: +44 (0)20 7213 0880Jo Turner, Sandy Jamieson, Ed Downes

ICR Healthcare (Media and Investor Relations) T: +44 (0)20 3707 5700Jessica Hodgson / Ashley Tapp / Philip Marriage

About 4basebio

4basebio (AIM: 4BB) is a Cambridge-based biotechnology company pioneering the use of synthetic DNA to enable next-generation therapeutics and vaccines. Through its proprietary enzymatic DNA synthesis platform, 4basebio produces GMP-grade synthetic DNA and mRNA with superior speed, purity, and scalability, overcoming the limitations of plasmid-based systems. The company offers application-specific DNA constructs tailored to the diverse needs of gene therapies, genome editing, mRNA production, and DNA vaccines, helping partners accelerate proof-of-concept studies and reach clinical milestones more efficiently while maintaining the highest standards of safety and quality.

For more information, visit 4basebio.com .