ESS Tech Inc美股招股说明书(2026-01-30版)

We are offering 3,471,428 shares of our common stock, par value $0.0001 per share, and, in lieu of common stock, pre-fundedwarrants to purchase up to 5,100,000 shares of our common stock (the “Pre-Funded Warrants”) to certain purchasers pursuant to thisprospectus supplement and the accompanying prospectus. The purchase price of each share of common stock is $1.75. The purchaseprice of each Pre-Funded Warrant equals the price at which shares of our common stock are being sold in this registered direct offeringminus $0.00001, and the exercise price of each Pre-Funded Warrant equals $0.00001 per share. This prospectus supplement alsorelates to the offering of the shares of common stock issuable upon the exercise of the Pre-Funded Warrants. The securities are beingsold in this offering to certain purchasers under a securities purchase agreement dated January 29, 2026 (the “Purchase Agreement”)among us and the purchasers identified on the signature pages thereto. Our common stock is listed on the New York Stock Exchange (“NYSE”) under the symbol “GWH.” The last reported sales price ofour common stock on January 28, 2026 was $1.68 per share. We have retained Aegis Capital Corp. to act as our exclusive placement agent, or the placement agent, in connection with the securitiesoffered by this prospectus supplement. The placement agent is not purchasing or selling any of the securities we are offering, and theplacement agent is not required to arrange the purchase or sale of any specific number of securities or dollar amount. We have agreed to pay to the placement agent the placement agent fees set forth in the table below, which assumes that we sell all ofthe securities offered by this prospectus supplement. See “Plan of Distribution” on pageS-18of this prospectus supplement for moreinformation regarding these arrangements. Offering pricePlacement agent’s fees(1) Proceeds, before expenses, to us (1)Includes a cash fee, equal to 6.0% of the gross proceeds raised in this offering, to be paid to the placement agent, provided, however, that the placement agent shallnot receive any commission for any securities sold in this offering to any of our directors, officers or certain other identified purchasers. We have also agreed toreimburse the placement agent for reasonable and documented out-of-pocket legal fees and disbursements incurred by the placement agent not to exceed anaggregate amount of $80,000. See “Plan of Distribution” for a complete description of the compensation to which the placement agent is entitled. Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on pageS-8of this prospectussupplement and in the documents incorporated by reference in this prospectus supplement and the accompanying prospectus.None of the Securities and Exchange Commission or any state securities commission has approved or disapproved of thesecurities being offered by this prospectus supplement or accompanying prospectus or determined if this prospectussupplement or accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense. Delivery of the securities offered hereby is expected to be made on or about January30, 2026, subject to satisfaction of customaryclosing conditions. Aegis Capital Corp. January 29, 2026 TABLE OF CONTENTS Prospectus Supplement About This Prospectus SupplementCautionary Note Regarding Forward-looking StatementsProspectus Supplement SummaryRisk FactorsDilutionUse of ProceedsDescription of the Securities We are OfferingPlan of DistributionLegal MattersExpertsWhere You Can Find More InformationIncorporation of Certain Documents by Reference Prospectus About this ProspectusProspectus SummaryRisk FactorsForward-Looking StatementsUse of ProceedsDescription of Capital StockDescription of Debt SecuritiesDescription of Depositary SharesDescription of WarrantsDescription of Subscription RightsDescription of Purchase ContractsDescription of UnitsPlan of DistributionLegal MattersExpertsWhere You Can Find More InformationIncorporation by Reference ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the Securitiesand Exchange Commission (the “SEC”), utilizing a “shelf” registration process. The document is in two parts. The first part is theprospectus supplement, which describes the specific terms of this offering. The second part is the prospectus, which provides moregeneral information about securities we may offer from time to time, some of which may not apply to this offering. Generally, whenwe refer to this “prospectus,” we are referring to both parts of this document combined. We urge you to carefully read this prospectussupplement and the prospectus, and the documents incorporated by reference herein and therein, before buying any of the securitiesbeing offered under this prospectus supplement. This prospectus supplement may add