Sera Prognostics Inc-A美股招股说明书(2026-03-18版)

Up to $40,000,000 ClassA Common Stock We have entered into an at-the-market sales agreement with William Blair& Company, L.L.C., or William Blair, as our sales agent, relating to the sharesof our ClassA common stock offered by this prospectus supplement. In accordance with the terms of the sales agreement, we may offer and sell sharesof our ClassA common stock having an aggregate offering price of up to $40,000,000 from time to time through William Blair, acting as sales agent. Thissales agreement utilizes the available capacity under our existing Form S-3 shelf registration statement filed in August2024. We are not obligated tomake any sales of Class A common stock, but pursuant to terms of the sales agreement and this prospectus supplement we now have the discretion todo so based on market conditions. No sales occurred under our prior ATM sales program. Our ClassA common stock is listed on The Nasdaq Global Market, under the symbol “SERA.” On March 17, 2026, the last reported sale price of ourClassA common stock was $2.01 per share. Sales of our ClassA common stock, if any, under this prospectus supplement will be made by any method permitted that is deemed to be an “at themarket offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act. William Blair is notrequired to sell any specific amount of securities, but will act as our sales agent using commercially reasonable efforts consistent with its normal tradingand sales practices, on mutually agreed terms between William Blair and us. There is no arrangement for funds to be received in any escrow, trust orsimilar arrangement. William Blair will be entitled to compensation at a commission of up to 3.0% of the aggregate gross sales price per share sold under the sales agreement.In connection with the sale of the ClassA common stock on our behalf, William Blair will be deemed to be an “underwriter” within the meaning of theSecurities Act, and the compensation of William Blair will be deemed to be underwriting commissions or discounts. We have also agreed to provideindemnification and contribution to William Blair with respect to certain liabilities, including liabilities under the Securities Act or the Securities ExchangeAct of 1934, as amended, or the Exchange Act. Our business and an investment in our ClassA common stock involve significant risks. These risks are described under thecaption “Risk Factors” beginning on page S-7 of this prospectus supplement and in the documents incorporated by referenceinto this prospectus supplement. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of thesesecurities or passed upon the accuracy or adequacy of this prospectus supplement. Any representation to the contrary is acriminal offense. William Blair The date of this prospectus supplement is March 18, 2026 Table of Contents TABLE OF CONTENTS PROSPECTUS SUPPLEMENT PAGEABOUT THIS PROSPECTUS SUPPLEMENTS-1PROSPECTUS SUPPLEMENT SUMMARYS-2THE OFFERINGS-6RISK FACTORSS-7CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTSS-9USE OF PROCEEDSS-11DILUTIONS-12DESCRIPTION OF CAPITAL STOCKS-14CERTAIN PROVISIONS OF DELAWARE LAW AND OF OUR AMENDED AND RESTATED CERTIFICATE OF INCORPORATION, ASAMENDED, AND RESTATED BYLAWSS-16PLAN OF DISTRIBUTIONS-20LEGAL MATTERSS-21EXPERTSS-21WHERE YOU CAN FIND MORE INFORMATIONS-22INCORPORATION OF INFORMATION BY REFERENCES-23 PROSPECTUS ABOUT THIS PROSPECTUSPROSPECTUS SUMMARYRISK FACTORSSPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTSUSE OF PROCEEDS PLAN OF DISTRIBUTION Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement is part of a shelf registration statement on Form S-3 that we filed with the Securities and Exchange Commission, orthe SEC, in August 2024 using a shelf registration process. Under the base prospectus included in the shelf registration statement, we may offersecurities having an aggregate offering price of up to $100,000,000. Under this prospectus supplement and the accompanying prospectus, wemay offer shares of our ClassA common stock having an aggregate offering price of up to $40,000,000 from time to time at prices and on termsto be determined by market conditions at the time of offering. The $40,000,000 of shares of our ClassA common stock that may be sold underthis prospectus supplement are included in the $100,000,000 of securities that may be sold under the registration statement. If the information contained in this prospectus supplement differs or varies from the information contained in any document incorporated byreference herein that was filed with the SEC before the date of this prospectus supplement, you should rely on the information set forth in thisprospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date (forexample, a subsequently filed document deemed incorporated by ref