Proposed Retail Offer

NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, DIRECTLY OR INDIRECTLY, IN WHOLE OR IN PART, TO US PERSONS OR INTO OR WITHIN THE UNITED STATES, AUSTRALIA, CANADA, SOUTH AFRICA OR JAPAN, OR ANY MEMBER STATE OF THE EEA, OR ANY OTHER JURISDICTION WHERE, OR TO ANY OTHER PERSON TO WHOM, TO DO SO MIGHT CONSTITUTE A VIOLATION OR BREACH OF ANY APPLICABLE LAW OR REGULATION. PLEASE SEE THE IMPORTANT NOTICE AT THE END OF THIS ANNOUNCEMENT.

THE COMMUNICATION OF THIS ANNOUNCEMENT AND ANY OTHER DOCUMENTS OR MATERIALS RELATING TO THE RETAIL OFFER AS A FINANCIAL PROMOTION IS ONLY BEING MADE TO, AND MAY ONLY BE ACTED UPON BY, THOSE PERSONS IN THE UNITED KINGDOM FALLING WITHIN ARTICLE 43 OF THE FINANCIAL SERVICES AND MARKETS ACT 2000 (FINANCIAL PROMOTION) ORDER 2005, AS AMENDED (WHICH INCLUDES AN EXISTING MEMBER OF 4BASEBIO PLC).  ANY INVESTMENT OR INVESTMENT ACTIVITY TO WHICH THIS ANNOUNCEMENT RELATES IS AVAILABLE ONLY TO SUCH PERSONS AND WILL BE ENGAGED IN ONLY BY SUCH PERSONS. THIS ANNOUNCEMENT IS FOR INFORMATIONAL PURPOSES ONLY, AND DOES NOT CONSTITUTE OR FORM PART OF ANY OFFER OR INVITATION TO SELL OR ISSUE, OR ANY SOLICITATION OF AN OFFER TO PURCHASE OR SUBSCRIBE FOR, ANY SECURITIES OF 4BASEBIO PLC.

15 October 2026

4basebio PLC

("4basebio" or the "Company")

Proposed Retail Offer

CAMBRIDGE, UK - 15 October 2026 - 4basebio PLC (AIM: 4BB), a specialist in synthetic DNA manufacturing for next-generation genomic medicines and advanced therapies, announces a retail offer via BookBuild (the "Retail Offer") of up to 97,087 new ordinary shares ("Ordinary Shares") of €1.00 each in the capital of the Company (the "Retail Offer Shares") at an issue price of 515 pence per Retail Offer Share (the "Issue Price").

In addition to the Retail Offer, earlier today the Company announced that it had conditionally raised gross proceeds of £15 million through a placing of 2,664,080 new Ordinary Shares (the "Placing Shares") and a subscription for 1,025,239 new Ordinary Shares by certain directors and existing shareholders (the "Subscription") including those pertaining to the Subscription & Set-Off Agreement as defined in the separate Placing and Subscription announcement released by the Company on 15 October 2026. The Retail Offer, the Placing and the Subscription together comprise the "Capital Raise", and the Placing Shares, Subscription Shares and Retail Offer Shares together comprise the "New Shares". The Placing, Subscription and Retail Offer are each being undertaken at the Issue Price. The Company is proposing to raise up to an additional £0.5 million (before expenses) through the Retail Offer, which would result in aggregate gross proceeds from the Capital Raise of up to £15.5 million. A separate announcement has been made regarding the results of the Placing and Subscription and their terms.

In recognition of their continued support to the Company, the Board believes that the Retail Offer provides the Company's eligible existing retail shareholders with an opportunity to participate in the Capital Raise at the Issue Price. The Issue Price represents a discount of approximately 8.4 per cent to the closing share price of 562.5 pence per existing Ordinary Share on 14 October 2026, being the last practicable date prior to the announcement of the Capital Raise.

For the avoidance of doubt, the Retail Offer is not part of the Placing or Subscription. Full details of the Capital Raise, including the background to and reasons for the Capital Raise and the proposed use of funds received under the Capital Raise, are set out in the separate Placing and Subscription announcement released by the Company on 15 October 2026.

The Retail Offer is conditional, inter alia, upon the passing of the Resolutions by Shareholders at the General Meeting, completion of the Placing and Subscription, and the Retail Offer Shares to be issued pursuant to the Retail Offer being admitted to trading on the AIM market operated by the London Stock Exchange ("Admission"). The Placing and Subscription are not conditional upon completion of the Retail Offer. Admission of the Retail Offer Shares is expected to take place at 8.00 a.m. on 10 November 2026.

The net proceeds of the Placing and Subscription and any proceeds of the Retail Offer will be used to support the Company's commercial development, complete the fit-out of Q-Arc, enhance R&D activities focused on reducing turnaround times and increasing yields, provide additional working capital and extend the Company's cash runway to H2 2028.

Expected Timetable in relation to the Retail Offer

Retail Offer opens	15 October 2026
Latest time and date for commitments under the Retail Offer	Noon on 21 October 2026
Results of the Retail Offer announced	As soon as reasonably practicable following the close of the Retail Offer on 21 October 2026
Admission and dealings in New Ordinary Shares issued pursuant to the Retail Offer commence	8.00 a.m. on 10 November 2026

Any changes to the expected timetable set out above will be notified by the Company through a Regulatory Information Service. References to times are to London times unless otherwise stated.

Dealing Codes

Ticker	4BB
ISIN for the Ordinary Shares	GB00BMCLYF79
SEDOL for the Ordinary Shares	BMCLYF7

Retail Offer

The Company values its retail shareholder base and believes that it is appropriate to provide its retail shareholders in the United Kingdom the opportunity to participate in the Retail Offer. The Company is therefore making the Retail Offer available in the United Kingdom through the financial intermediaries which will be listed, subject to certain access restrictions, on the following website: https://www.bookbuild.live/deals/G7VL2Q/authorised-intermediaries. Cavendish Capital Markets Limited will be acting as retail offer coordinator in relation to this Retail Offer (the "Retail Offer Coordinator").

Existing retail shareholders can contact their broker or wealth manager to participate in the Retail Offer. In order to participate in the Retail Offer, each intermediary must be on-boarded onto the BookBuild platform and agree to the final terms and the retail offer terms and conditions, which regulate, inter alia, the conduct of the Retail Offer on market standard terms and provide for the payment of commission to any intermediary that elects to receive a commission and/or fee (to the extent permitted by the FCA Handbook Rules) from the Retail Offer Coordinator (on behalf of the Company).

Any expenses incurred by any intermediary are for its own account. Investors should confirm separately with any intermediary whether there are any commissions, fees or expenses that will be applied by such intermediary in connection with any application made through that intermediary pursuant to the Retail Offer.

The Retail Offer will be open to eligible investors in the United Kingdom at 4.00 p.m. on 15 October 2026. The Retail Offer is expected to close at noon on 21 October 2026. Investors should note that financial intermediaries may have earlier closing times. The Retail Offer may close early if it is oversubscribed.

If any intermediary has any questions about how to participate in the Retail Offer on behalf of existing retail shareholders, please contact the Retail Offer Coordinator or BookBuild at [email protected].

The Retail Offer the subject of this announcement is and will, at all times, only be made to, directed at and may only be acted upon by those persons who are, shareholders in the Company. To be eligible to participate in the Retail Offer, applicants must meet the following criteria before they can submit an order for Retail Offer Shares: (i) be a customer of one of the participating intermediaries listed on the above website; (ii) be resident in the United Kingdom and (iii) be a shareholder in the Company (which may include individuals aged 18 years or over, companies and other bodies corporate, partnerships, trusts, associations and other unincorporated organisations and includes persons who hold their shares in the Company directly or indirectly through a participating intermediary). For the avoidance of doubt, persons who only hold CFDs, Spreadbets and/or similar derivative instruments in relation to shares in the Company are not eligible to participate in the Retail Offer.

The Company reserves the right to scale back any order at its discretion. The Company reserves the right to reject any application for subscription under the Retail Offer without giving any reason for such rejection.

It is vital to note that once an application for Retail Offer Shares has been made and accepted via an intermediary, it cannot be withdrawn.

The New Ordinary Shares will, when issued, be credited as fully paid and will rank pari passu in all respects with existing Ordinary Shares including the right to receive all dividends and other distributions declared, made or paid after their date of issue.

The Retail Offer is offered in the United Kingdom under an exemption from the prohibition of public offers specified in Part 1 of Schedule 1 of the Public Offers and Admissions to Trading Regulations 2024.

The Retail Offer is not being made into any jurisdiction other than the United Kingdom or to US Persons (as defined in Regulation S of the US Securities Act 1933, as amended).

No offering document, prospectus or admission document has been or will be prepared or submitted to be approved by the Financial Conduct Authority (or any other authority) in relation to the Retail Offer, and investors' commitments will be made solely on the basis of the information contained in this announcement and information that has been published by or on behalf of the Company prior to the date of this announcement by notification to a Regulatory Information Service in accordance with the Financial Conduct Authority's Disclosure Guidance and Transparency Rules and the Market Abuse Regulation (EU Regulation No. 596/2014) ("MAR") as it forms part of United Kingdom law by virtue of the European Union (Withdrawal) Act 2018 (as amended).

There is a minimum subscription of £100 per investor under the terms of the Retail Offer which is open to investors in the United Kingdom subscribing via the intermediaries which will be listed, subject to certain access restrictions, on the following website: https://www.bookbuild.live/deals/G7VL2Q/authorised-intermediaries. There is no maximum application amount to apply in the Retail Offer. The terms and conditions on which investors subscribe will be provided by the relevant financial intermediaries including relevant commission or fee charges.

Investors should make their own investigations into the merits of an investment in the Company. Nothing in this announcement amounts to a recommendation to invest in the Company or amounts to investment, taxation or legal advice.

It should be noted that a subscription for Retail Offer Shares and investment in the Company carries a number of risks. Investors should take independent advice from a person experienced in advising on investment in securities such as the Retail Offer Shares if they are in any doubt.

For further information, please contact:

4basebio PLC

+44 (0)12 2396 7943

Dr. Amy Walker - Chief Executive Officer

Richard Bungay - Chief Financial Officer

Cavendish Capital Markets Limited (Retail Offer Coordinator and Joint Corporate Broker)

T: +44 (0)20 7220 0500

Geoff Nash, Andrea Callaghan - Corporate Finance

Nigel Birks - Healthcare Specialist Sales

Cairn Financial Advisers LLP (Nominated Adviser)

T: +44 (0)20 7213 0880

Jo Turner, Sandy Jamieson, Ed Downes

Further information on the Company can be found on its website at: https://www.4basebio.com

The Company's LEI is 213800E2DX9EAIUNCB30.

This announcement should be read in its entirety. In particular, the information in the "Important Notices" section of the announcement should be read and understood.

Important Notices

The Retail Offer is only open to investors in the United Kingdom who fall within Article 43 of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (which includes an existing member of the Company).

This announcement and the information contained herein is not for release, publication or distribution, directly or indirectly, in whole or in part, in or into or from the United States (including its territories and possessions, any state of the United States and the District of Columbia (the "United States" or "US")), Australia, Canada, Japan, the Republic of South Africa, any member state of the EEA or any other jurisdiction where to do so might constitute a violation of the relevant laws or regulations of such jurisdiction.

The Retail Offer Shares have not been and will not be registered under the US Securities Act of 1933, as amended (the "US Securities Act") or under the applicable state securities laws of the United States and may not be offered or sold directly or indirectly in or into the United States or to or for the account or benefit of any US person (within the meaning of Regulation S under the US Securities Act) (a "US Person"). No public offering of the Retail Offer Shares is being made in the United States. The Retail Offer Shares are being offered and sold outside the United States in "offshore transactions", as defined in, and in compliance with, Regulation S under the US Securities Act. In addition, the Company has not been, and will not be, registered under the US Investment Company Act of 1940, as amended.

This announcement does not constitute an offer to sell or issue or a solicitation of an offer to buy or subscribe for Retail Offer Shares in the United States, Australia, Canada, New Zealand, Japan, the Republic of South Africa, any member state of the EEA or any other jurisdiction in which such offer or solicitation is or may be unlawful. No public offer of the securities referred to herein is being made in any such jurisdiction.

The distribution of this announcement may be restricted by law in certain jurisdictions and persons into whose possession any document or other information referred to herein comes should inform themselves about and observe any such restriction. Any failure to comply with these restrictions may constitute a violation of the securities laws of any such jurisdiction.

Cavendish Capital Markets Limited is authorised and regulated in the United Kingdom by the Financial Conduct Authority, is acting exclusively for the Company and for no-one else and will not regard any other person (whether or not a recipient of this announcement) as its client in relation to the Retail Offer and will not be responsible to anyone other than the Company for providing the protections afforded to its clients, nor for providing advice in connection with the Retail Offer, Admission and the other arrangements referred to in this announcement.

The value of Ordinary Shares and the income from them is not guaranteed and can fall as well as rise due to stock market and currency movements. When you sell your investment, you may get back less than you originally invested. Figures refer to past performance and past performance is not a reliable indicator of future results. Returns may increase or decrease as a result of currency fluctuations.

Certain statements in this announcement are forward-looking statements which are based on the Company's expectations, intentions and projections regarding its future performance, anticipated events or trends and other matters that are not historical facts. These forward-looking statements, which may use words such as "aim", "anticipate", "believe", "intend", "estimate", "expect" and words of similar meaning, include all matters that are not historical facts. These forward-looking statements involve risks, assumptions and uncertainties that could cause the actual results of operations, financial condition, liquidity and dividend policy and the development of the industries in which the Company's businesses operate to differ materially from the impression created by the forward-looking statements. These statements are not guarantees of future performance and are subject to known and unknown risks, uncertainties and other factors that could cause actual results to differ materially from those expressed or implied by such forward-looking statements. Given those risks and uncertainties, prospective investors are cautioned not to place undue reliance on forward-looking statements.

These forward-looking statements speak only as at the date of this announcement and cannot be relied upon as a guide to future performance. Each of the Company and Cavendish Capital Markets Limited expressly disclaims any obligation or undertaking to update or revise any forward-looking statements contained herein to reflect actual results or any change in the assumptions, conditions or circumstances on which any such statements are based unless required to do so by the Financial Conduct Authority, the London Stock Exchange or applicable law.

The information in this announcement is for background purposes only and does not purport to be full or complete. None of Cavendish Capital Markets Limited or any of its affiliates, accepts any responsibility or liability whatsoever for, or makes any representation or warranty, express or implied, as to this announcement, including the truth, accuracy or completeness of the information in this announcement (or whether any information has been omitted from the announcement) or any other information relating to the Company or associated companies, whether written, oral or in a visual or electronic form, and howsoever transmitted or made available or for any loss howsoever arising from any use of the announcement or its contents or otherwise arising in connection therewith. Each of Cavendish Capital Markets Limited and its affiliates, accordingly disclaims all and any liability whether arising in tort, contract or otherwise which it might otherwise be found to have in respect of this announcement or its contents or otherwise arising in connection therewith.

Any indication in this announcement of the price at which the Ordinary Shares have been bought or sold in the past cannot be relied upon as a guide to future performance. Persons needing advice should consult an independent financial adviser. No statement in this announcement is intended to be a profit forecast and no statement in this announcement should be interpreted to mean that earnings or target dividend per share of the Company for the current or future financial years would necessarily match or exceed the historical published earnings or dividends per share of the Company.

Neither the content of the Company's website (or any other website) nor the content of any website accessible from hyperlinks on the Company's website (or any other website) is incorporated into or forms part of this announcement. The Retail Offer Shares to be issued or sold pursuant to the Retail Offer will not be admitted to trading on any stock exchange other than the London Stock Exchange.

UK Product Governance Requirements

Solely for the purposes of the product governance requirements of Chapter 3 of the FCA Handbook Product Intervention and Product Governance Sourcebook (the "UK MiFIR Product Governance Requirements"), and disclaiming all and any liability, whether arising in tort, contract or otherwise, which any "manufacturer" (for the purposes of the UK MiFIR Product Governance Requirements) may otherwise have with respect thereto, the Retail Offer Shares have been subject to a product approval process, which has determined that the Retail Offer Shares are: (i) compatible with an end target market of retail investors and investors who meet the criteria of professional clients and eligible counterparties, each as defined in paragraphs 3.5 and 3.6 of COBS; and (ii) eligible for distribution through all permitted distribution channels (the "Target Market Assessment"). Notwithstanding the Target Market Assessment, distributors should note that: the price of the Retail Offer Shares may decline and investors could lose all or part of their investment; the Retail Offer Shares offer no guaranteed income and no capital protection; and an investment in the Retail Offer Shares is compatible only with investors who do not need a guaranteed income or capital protection, who (either alone or in conjunction with an appropriate financial or other adviser) are capable of evaluating the merits and risks of such an investment and who have sufficient resources to be able to bear any losses that may result therefrom. The Target Market Assessment is without prejudice to any contractual, legal or regulatory selling restrictions in relation to the Retail Offer.

For the avoidance of doubt, the Target Market Assessment does not constitute: (a) an assessment of suitability or appropriateness for the purposes of Chapters 9A or 10A respectively of COBS; or (b) a recommendation to any investor or group of investors to invest in, or purchase, or take any other action whatsoever with respect to the Retail Offer Shares. Each distributor is responsible for undertaking its own target market assessment in respect of the Retail Offer Shares and determining appropriate distribution channels.

EU Product Governance Requirements

Solely for the purposes of the product governance requirements contained within: (a) EU Directive 2014/65/EU on markets in financial instruments, as amended ("MiFID II"); (b) Articles 9 and 10 of Commission Delegated Directive (EU) 2017/593 supplementing MiFID II; and (c) local implementing measures (together, the "MiFID II Product Governance Requirements"), and disclaiming all and any liability, whether arising in tort, contract or otherwise, which any "manufacturer" (for the purposes of the MiFID II Product Governance Requirements) may otherwise have with respect thereto, the Retail Offer Shares have been subject to a product approval process, which has determined that the Retail Offer Shares are: (i) compatible with an end target market of retail investors and investors who meet the criteria of professional clients and eligible counterparties, each as defined in MiFID II; and (ii) eligible for distribution through all distribution channels as are permitted by MiFID II (the "EU Target Market Assessment"). Notwithstanding the EU Target Market Assessment, distributors should note that: the price of the Retail Offer Shares may decline and investors could lose all or part of their investment; the Retail Offer Shares offer no guaranteed income and no capital protection; and an investment in the Retail Offer Shares is compatible only with investors who do not need a guaranteed income or capital protection, who (either alone or in conjunction with an appropriate financial or other adviser) are capable of evaluating the merits and risks of such an investment and who have sufficient resources to be able to bear any losses that may result therefrom. The EU Target Market Assessment is without prejudice to the requirements of any contractual, legal or regulatory selling restrictions in relation to the Retail Offer.

For the avoidance of doubt, the EU Target Market Assessment does not constitute: (a) an assessment of suitability or appropriateness for the purposes of MiFID II; or (b) a recommendation to any investor or group of investors to invest in, or purchase or take any other action whatsoever with respect to the Retail Offer Shares. Each distributor is responsible for undertaking its own target market assessment in respect of the Retail Offer Shares and determining appropriate distribution channels.