Allurion Technologies Inc. American stock prospectus (version dated 2025-05-20)

Up to 56,548,268 Shares of Common Stock This prospectus supplement no. 23 (this “Prospectus Supplement”) amends and supplements the prospectus dated December15, 2023 (as supplementedor amended from time to time, the “Prospectus”) which forms part of our Registration Statement on FormS-1/A(Registration StatementNo.333-274564).This Prospectus Supplement is being filed to update and supplement the information included or incorporated by reference in theProspectus with the information contained in our Quarterly Report on Form10-Q,filed with the Securities and Exchange Commission (the “SEC”) on This Prospectus Supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered orutilized except in combination with, the Prospectus, including any amendments or supplements thereto. This Prospectus Supplement should be read in Our common stock is listed on The New York Stock Exchange (“NYSE”) under the symbol “ALUR” and our public warrants are listed on the NYSEunder the symbol “ALUR.WS”. On May19, 2025, the last quoted sale price for shares of our common stock as reported on the NYSE was $3.06 per We are an “emerging growth company” under applicable federal securities laws and will be subject to reduced public company reportingrequirements. Investing in our securities involves a high degree of risk. Before buying any securities, you should carefully readthe discussion of the risks of investing in our securities in “Risk Factors” beginning on page 52 of the Prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to beissued under the Prospectus or determined if the Prospectus is truthful or complete. Any representation to the contrary is a criminal offense. Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule405 of RegulationS-T(§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with Indicate by check mark whether the registrant is a shell company (as defined in Rule12b-2of the Exchange Act).Yes☐No☒ As of May12, 2025, the registrant had 7,457,758 shares of common stock, $0.0001 par value per share, outstanding. Table of Contents PARTI.FINANCIAL INFORMATION Item 1.Financial Statements (Unaudited)Condensed Consolidated Balance Sheets Item 3.Quantitative and Qualitative Disclosures About Market RiskItem 4.Controls and ProceduresPARTII.OTHER INFORMATIONItem 1.Legal ProceedingsItem 1A.Risk FactorsItem 2.Unregistered Sales of Equity Securities and Use of ProceedsItem 3.Defaults Upon Senior SecuritiesItem 4.Mine Safety DisclosuresItem 5.Other InformationItem 6.Exhibits Signatures Table of Contents SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS This Quarterly Report on Form10-Qcontains forward-looking statements within the meaning of Section27A of the Securities Act of 1933, asamended, and Section21E of the Securities Exchange Act of 1934, as amended. These forward-looking statements, which are not purely historical,include, but are not limited to, statements regarding the plans, strategies and prospects, both business and financial, of Allurion Technologies, Inc.(“Allurion”, the “Company”, “we”, “our”, or “us”). Forward-looking statements involve known and unknown risks, uncertainties, assumptions and other Generally, statements that are not historical facts, including statements concerning possible or assumed future actions, business strategies, events,or results of operations, are forward-looking statements. These statements may be preceded by, followed by or include the words “believes”,“estimates”, “expects”, “projects”, “target”, “goal”, “forecasts”, “may”, “will”, “potential”, “should”, “would”, “could”, “future”, “seeks”, “plans”,“predicts”, “propose”, “scheduled”, “anticipates”, “intends”, or similar expressions. Such statements are based on the beliefs and assumptions of the Forward-looking statements in this Quarterly Report on Form10-Qinclude, but are not limited to, statements about the ability of Allurion to: •realize the benefits expected from the business combination between Allurion and Compute Health Acquisition Corp. pursuant to thatcertain Business Combination Agreement, dated as of February9, 2023, by and among Allurion, Allurion Technologies, LLC, which waspreviously known as Allurion Technologies Opco, Inc. (formerly Allurion Technologies, Inc.) prior to the consummation of the Business •successfully defend litigation that may be instituted against Allurion;•manage various conflicts of interest that could arise among us and our affiliates, investors, directors, and officers; •successfully deploy our cash and cash equivalents and procee