Arqit Quantum (ARQQ) updates resale registration for 4.72M shares, warrants

Rhea-AI Filing Summary

Arqit Quantum Inc. files a prospectus supplement updating a resale registration covering 4,717,000 Ordinary Shares and 6,266,667 warrants, and noting 595,666 Ordinary Shares issuable upon exercise of registered warrants.

The supplement updates the selling securityholders table to reflect permitted sales and distributions and states the share counts reflect a 25-to-1 reverse share split effected on September 25, 2024. The table bases percentages on 24,090,585 ordinary shares outstanding as of May 19, 2026.

Insights

Securities Attorney

Supplement updates resale registrations and selling holder allocations.

The supplement modifies the selling securityholders table to reflect sales and distributions made under the prospectus Plan of Distribution. It confirms registered amounts of 4,717,000 Ordinary Shares, 6,266,667 warrants, and 595,666 shares issuable upon exercise.

Timing and cash‑flow treatment are governed by the existing prospectus terms; the supplement preserves prior qualifiers and the reverse split disclosure of September 25, 2024.

Capital Markets Analyst

Resale registration maintained; major holders and outstanding bases are clarified.

The table shows large holdings by Heritage Assets SCSP (shown as 9,251,492 shares, 38.4% of the stated base) and Ropemaker Nominees Limited (shown as 1,870,345 shares, 7.8%). Percentages use May 19, 2026 baselines.

Market impact depends on selling holders' activity under the permitted distribution methods; cash‑flow treatment for sales is not restated in this supplement.

Key Figures

Registered ordinary shares: 4,717,000 shares Registered warrants: 6,266,667 warrants Shares issuable upon exercise: 595,666 shares +3 more

6 metrics

Registered ordinary shares 4,717,000 shares resale registration stated in prospectus supplement

Registered warrants 6,266,667 warrants warrants to purchase Ordinary Shares registered for resale

Shares issuable upon exercise 595,666 shares Ordinary Shares issuable upon exercise of Public and Private Warrants

Shares outstanding basis 24,090,585 shares figure used to calculate percentages, as of <date>May 19, 2026</date>

Heritage Assets holding 9,251,492 shares Heritage Assets SCSP beneficial ownership, shown as <percent>38.4%</percent>

Ropemaker Nominees holding 1,870,345 shares Ropemaker Nominees Limited beneficial ownership, shown as <percent>7.8%</percent>

Key Terms

selling securityholders, Public Warrants, 25-to-1 reverse share split

3 terms

selling securityholders regulatory

"updates table of the Selling Securityholders to reflect certain sales and distributions"

Selling securityholders are existing owners of a company's stocks or other tradable claims who are offering some or all of their holdings for sale in a public offering or secondary transaction. Investors watch these sellers because large or insider sales can increase the number of shares available, put downward pressure on price, and signal insiders’ views about future prospects—much like many people selling tickets at once can change the market for an event.

Public Warrants financial

"shares issuable by us upon the exercise of the Public Warrants"

Public warrants are tradable securities that give the holder the right to buy a company’s stock at a fixed price before a set expiration date. Like a coupon that lets you purchase shares later at a preset price, they matter to investors because using them can bring new cash into the company but also increase the total number of shares outstanding, which can dilute existing ownership and influence the stock’s price and potential gains.

25-to-1 reverse share split market

"On September 25, 2024, Arqit effected a 25-to-1 reverse share split"

Offering Details

resale/secondary

Offering

Offering Type resale/secondary

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/21/2026 - 08:26 AM Learn about SEC filing dates

FAQ

What did the Arqit (ARQQ) prospectus supplement register?

It registers 4,717,000 Ordinary Shares, 6,266,667 warrants, and 595,666 shares issuable upon warrant exercise. The supplement updates the selling holders table and reflects a 25-to-1 reverse split.

Does the supplement change who can sell Arqit (ARQQ) shares?

No—this supplement updates the table of selling securityholders to reflect permitted sales and distributions. The sale rights remain governed by the Prospectus' Plan of Distribution.

How many Arqit (ARQQ) shares were used to calculate percentages?

Percentages are based on 24,090,585 ordinary shares outstanding, which includes shares outstanding and exercisable warrants as of May 19, 2026.

Who are the largest selling holders listed in the supplement?

The table shows Heritage Assets SCSP holding 9,251,492 shares (38.4%) and Ropemaker Nominees Limited holding 1,870,345 shares (7.8%) on the disclosed basis.

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-259982

PROSPECTUS SUPPLEMENT

(To Prospectus dated November 22, 2022)

Arqit Quantum Inc.

4,717,000 Ordinary Shares

6,266,667 Warrants to Purchase Ordinary Shares

595,666 Ordinary Shares Underlying Warrants

This prospectus supplement updates and amends certain information contained in the prospectus dated November 22, 2022 (the “Prospectus”) covering the offer and sale from time to time by the selling securityholders named in the Prospectus of up to 4,717,000 of our ordinary shares, par value $0.0025 per share (“Ordinary Shares”), and 6,266,667 warrants to purchase Ordinary Shares. The Prospectus also relates to the issuance by us of up to 595,666 Ordinary Shares, that are issuable by us upon the exercise of the Public Warrants (as defined in the Prospectus), which were previously registered, and the Private Warrants (as defined in the Prospectus). You should read this prospectus supplement in conjunction with the Prospectus. This prospectus supplement is not complete without, and may not be utilized except in connection with, the Prospectus, including any amendments or supplements thereto.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” beginning on page 9 of the Prospectus, and under similar headings in any amendment or supplements to the Prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Prospectus or this prospectus supplement. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is May 21, 2026

EXPLANATORY NOTE

This prospectus supplement updates and supplements the Prospectus to update table of the Selling Securityholders (as defined in the Prospectus) to reflect certain sales and distributions that have been made as permitted under the section entitled “Plan of Distribution” included in the Prospectus. On September 25, 2024, Arqit Quantum Inc. effected a 25-to-1 reverse share split, which is reflected in the numbers included in this prospectus supplement.

Updated Table of Selling Securityholders

Where the name and information of a Selling Securityholder identified in the table below also appears in the table and the related footnotes in the Prospectus on pages 29, 30 and 31, the information set forth in the table below and the related footnotes regarding that Selling Securityholder supersedes and replaces the information regarding such Selling Securityholder in the Prospectus. The percentages in the following table are based on 24,090,585 ordinary shares outstanding, including (i) 17,402,411 ordinary shares issued and outstanding as of May 19, 2026, (ii) 6,582,734 ordinary shares underlying our currently exercisable outstanding warrants, and (iii) 105,440 shares underlying outstanding equity incentives that are exercisable or that will become exercisable within 60 days following May 19, 2026.

		Ordinary Shares																				Warrants
		Beneficially								Number				Beneficially								Beneficially								Number				Beneficially
		Owned								Registered				Owned								Owned								Registered				Owned
		Prior to Offering								for Sale				After Offering								Prior to Offering								for Sale				After Offering
Name		Number				Percent				Hereby				Number				Percent				Number				Percent				Hereby				Number				Percent
Adam Hall(1)			1,000				*				1,000				—				—				—				—				—				—				—
Adam M. Aron(2)			800				*				800				—				—				—				—				—				—				—
Garth Ritchie(3)			105,049				*				5,925				—				—				—				—				—				—				—
Geoffrey Taylor(4)			16,227				*				16,227				—				—				—				—				—				—				—
Giulia Nobili(5)			6,000				*				6,000				—				—				—				—				—				—				—
Heritage Assets SCSP(6)			9,251,492				38.4	%			466,122				—				—				607,006				4.7	%			607,006				—				—
Nicholas Taylor(7)			886				*				658				—				—				—				—				—				—				—
Patricia Taylor(4)			800				*				800				—				—				—				—				—				—				—
Ropemaker Nominees Limited(8)			1,870,345				7.8	%			647,700				—				—				—				—				—				—				—
The Evolution Technology Fund II SCSp(9)			276,259				1.1	%			276,259				—				—				—				—				—				—				—
Trevor Barker(10)			151,612				*				151,612				—				—				—				—				—				—				—
UK FF Nominees Limited(11)			166,067				*				166,067				—				—				—				—				—				—				—

*	Less than 1.0%.
(1)	The business address of Adam Hall is 3 Orchard Place, London SW1H 0BF, United Kingdom. Mr. Hall is a former employee of the Company’s primary operating subsidiary, Arqit Limited.
(2)	The business address of Adam M. Aron is c/o AMC Entertainment, 11500 Ash Street, Leawood, KS 66211, USA.
(3)	The business address of Garth Ritchie is 3 Orchard Place, London SW1H 0BF, United Kingdom. Includes 73,562 shares underlying September 2024 Investor Warrants that are currently exercisable, and restricted stock units that will vest within 60 days following May 19, 2026.
(4)	The business address for each of Geoffrey Taylor and Patricia Taylor is 3 Orchard Place, London SW1H 0BF, United Kingdom.
(5)	The business address of Giulia Nobili is L’Estoril, 31 Avenue Princesse Grace, 98000, Monaco.
(6)	The business address for Heritage Assets SCSP is c/o Heritage Services SAM Attn: Cristina Levis, 7 Rue Du Gabian, 98000, Monaco. Includes 24,280.24 shares underlying Business Combination Warrants, 230,770 shares underlying September 2023 Investor Warrants and 4,600,000 shares underlying September 2024 Investor Warrants that are currently exercisable.

(7)	The business address of Nicholas Taylor is 5 Anley Street, St Helier, Jersey, Channel Islands, JE2 3QE.
(8)	The business address for Ropemaker Nominees Limited is 1st Floor, Royal Chambers, St Julian’s Avenue, St Peter Port, Guernsey GY1 3JX. Notion Capital Managers LLP has sole investment and voting power over Ropemaker Nominees Limited’s shares. The investment decisions of Notion Capital Managers LLP are made by the majority vote of an investment committee comprised of five members, including Stephen Chandler. Under the so-called “rule of three,” if voting and dispositive decisions regarding an entity’s securities are made by three or more individuals, and a voting or dispositive decision requires the approval of at least a majority of those individuals, then none of the individuals is deemed a beneficial owner of the entity’s securities. Based upon the foregoing analysis, no individual member of the investment committee of Notion Capital Managers LLP exercises voting or dispositive control over any of the securities over which it holds sole investment and voting power. Accordingly, Mr. Chandler is not deemed to have or share beneficial ownership of such shares. Includes 76,381 shared underlying September 2023 Investor Warrants and 600,000 shares underlying September 2024 Investor Warrants that are currently exercisable.
(9)	The business address of The Evolution Technology Fund II, SCSp is 15, Boulevard Friedrich Wilhelm Raiffeisen, L 2411. Luxembourg. Evolution Equity Partners II Sarl is the general partner of The Evolution Technology Fund II, SCSp. and has sole investment and voting power over the shares held by The Evolution Technology Fund II, SCSp.
(10)	The business address of Trevor Barker is 3 Orchard Place, London SW1H 0BF, United Kingdom.
(11)	The business address of UK FF Nominees Limited is 5 Churchill Place, 10th Floor, London, E14 5HU, United Kingdom. The Secretary of State for Business and Trade (formerly the Secretary of State for Business, Energy and Industrial Strategy) has sole investment and voting power over the shares held by UK FF Nominees Limited.