Alto Neuroscience Inc美股招股说明书(2026-07-14版)

We are offering 3,776,436 shares of our common stock, par value $0.0001 per share, or the commonstock. The offering price for each share of common stock is $26.48. Our common stock is listed on The New York Stock Exchange under the symbol “ANRO.” The lastreported sale price of our common stock on The New York Stock Exchange on July10, 2026 was $26.48 pershare. We are an “emerging growth company” and eligible to use the requirements of a “smaller reportingcompany,” each as defined under the U.S. federal securities laws, and, as such, have elected to comply withcertain reduced public company reporting requirements as applicable to such types of companies and mayelect to do so in future filings. See “Prospectus Supplement Summary — Implications of Being an EmergingGrowth Company and a Smaller Reporting Company.” Investing in our securities involves a high degree of risk. Before making an investment decision, you shouldreview carefully the risks and uncertainties described under the heading “Risk Factors” on pageS-11of thisprospectus, page8of the accompanying prospectus and under similar headings in the documents incorporatedby reference into this prospectus supplement and the accompanying prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved ordisapproved of these securities or determined if this prospectus supplement or the accompanying prospectus istruthful or complete. Any representation to the contrary is a criminal offense. (1)See “Underwriting” for a description of the compensation payable to the underwriters. The underwriters expect to deliver the shares against payment in New York, New York on July14,2026. Prospectus Supplement dated July13, 2026 TABLE OF CONTENTS PROSPECTUS SUPPLEMENT ABOUT THIS PROSPECTUS SUPPLEMENTS-1SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTSS-3PROSPECTUS SUPPLEMENT SUMMARYS-5THE OFFERINGS-9RISK FACTORSS-11USE OF PROCEEDSS-13DILUTIONS-14UNDERWRITINGS-16LEGAL MATTERSS-24EXPERTSS-24WHERE YOU CAN FIND MORE INFORMATIONS-25INCORPORATION OF CERTAIN INFORMATION BY REFERENCES-26PROSPECTUSABOUT THIS PROSPECTUS1PROSPECTUS SUMMARY3RISK FACTORS8SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS9USE OF PROCEEDS11DESCRIPTION OF CAPITAL STOCK12DESCRIPTION OF DEBT SECURITIES20DESCRIPTION OF WARRANTS27LEGAL OWNERSHIP OF SECURITIES29PLAN OF DISTRIBUTION32LEGAL MATTERS35EXPERTS35WHERE YOU CAN FIND ADDITIONAL INFORMATION35INCORPORATION OF CERTAIN INFORMATION BY REFERENCE36 ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement is part of a “shelf” registration statement onForm S-3 (File No. 333-284667) that we filed with the Securities and Exchange Commission, or the SEC, on February3, 2025, andwhich was declared effective by the SEC on February11, 2025. This document is in two parts. The first partis this prospectus supplement, which describes the specific terms of this offering of common stock and alsoadds to and updates information contained in the accompanying prospectus and the documents incorporatedby reference herein. The second part, the accompanying prospectus, provides more general information.Generally, when we refer to this prospectus, we are referring to both parts of this document combined. Theinformation included or incorporated by reference in this prospectus supplement also adds to, updates andchanges information contained or incorporated by reference in the accompanying prospectus. Before buying any of the shares of common stock offered hereby, we urge you to read carefully thisprospectus supplement and the accompanying prospectus, together with the information incorporated hereinby reference as described below under the heading “Incorporation of Certain Information by Reference.”These documents contain important information that you should consider when making your investmentdecision. To the extent there is a conflict between the information contained in this prospectus supplementand the information contained in the accompanying prospectus or any document incorporated by referencetherein filed prior to the date of this prospectus supplement, you should rely on the information in thisprospectus supplement; provided that if any statement in one of these documents is inconsistent with astatement in another document having a later date — for example, a document incorporated by reference inthe accompanying prospectus — the statement in the document having the later date modifies or supersedesthe earlier statement. If the description of the offering varies between any free writing prospectus we haveauthorized for use in connection with this offering and this prospectus supplement, you should rely on theinformation in such free writing prospectus. We further note that the representations, warranties and covenants made by us in any agreement that isfiled as an exhibit to any document that is incorporated by reference herein were made solely for the benefitof the parties to such agreement, including, in some cases,