Supplemental Prospectus (Form 424B3)

Filed Pursuant to Rule 424(b)(3)
Registration No. 333-279902

Prospectus Supplement No. 22

(To Prospectus dated October 7, 2024)

ALLURION TECHNOLOGIES, INC.

Up to 65,211,325 Shares of Common Stock

This prospectus supplement no. 22 (this "Prospectus Supplement") amends and supplements the prospectus dated October 7, 2024 (as supplemented or amended from time to time, the "Prospectus") which forms part of our Registration Statement on Form S-1 (Registration Statement No. 333-279902). This Prospectus Supplement is being filed to update and supplement the information included or incorporated by reference in the Prospectus with the information contained in our Current Report on Form 8-K, filed with the Securities and Exchange Commission (the "SEC") on December 19, 2025 (the "8-K"). Accordingly, we have attached the 8-K to this Prospectus Supplement.

This Prospectus Supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This Prospectus Supplement should be read in conjunction with the Prospectus, and if there is any inconsistency between the information in the Prospectus and this Prospectus Supplement, you should rely on this Prospectus Supplement.

Our common stock is listed on The New York Stock Exchange ("NYSE") under the symbol "ALUR" and our public warrants are listed on the NYSE under the symbol "ALUR.WS". On December 19, 2025, the last quoted sale price for shares of our common stock as reported on the NYSE was $1.47 per share, and the last quoted sale price for our public warrants as reported on the NYSE was $0.02 per warrant.

We are an "emerging growth company" under applicable federal securities laws and will be subject to reduced public company reporting requirements.

Investing in our securities involves a high degree of risk. Before buying any securities, you should carefully read the discussion of the risks of investing in our securities in "Risk Factors" beginning on page 23 of the Prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under the Prospectus or determined if the Prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this Prospectus Supplement is December 22, 2025.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 18, 2025

Allurion Technologies, Inc.

(Exact name of Registrant as Specified in Its Charter)

Registrant's Telephone Number, Including Area Code: (508) 647-4000

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 5.07 Submission of Matters to a Vote of Security Holders.

On December 18, 2025, Allurion Technologies, Inc. (the "Company") held its 2025 Annual Meeting of Stockholders (the "Annual Meeting") to consider and vote on the seven proposals set forth below, each of which is described in detail in the Company's Definitive Proxy Statement on Schedule 14A filed with the Securities and Exchange Commission on November 24, 2025 (the "Proxy Statement").

The following actions were taken at such meeting:

The proposal to adjourn the Annual Meeting, if necessary, to permit further solicitation and vote of proxies in the event that there were insufficient votes in favor of Proposals 3, 4, 5, 6 and 7 was not voted upon at the Annual Meeting since there were sufficient votes to approve Proposals 3, 4, 5, 6 and 7.

No other matters were submitted to or voted on by the Company's stockholders at the Annual Meeting.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.