ESS Tech Inc美股招股说明书(2025-12-11版)

We have entered into a Sales Agreement, dated November13, 2025, (the “Sales Agreement”), with Yorkville Securities, LLC(“Yorkville Securities”), BMO Capital Markets Corp. (“BMO”), Canaccord Genuity LLC (“Canaccord”), Needham & Company, LLC(“Needham”) and Stifel, Nicolaus & Company, Incorporated (“Stifel”) (each of Yorkville Securities, BMO, Canaccord, Needham andStifel individually an “Agent” and collectively, the “Agents”) relating to shares of our common stock, $0.0001 par value per share,offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the Sales Agreement, wemay offer and sell shares of our common stock under this prospectus supplement having an aggregate gross sales price of up to Our common stock is listed on the New York Stock Exchange (the “NYSE”) under the symbol “GWH.” On December 10, 2025,the last quoted sale price for our common stock as reported on the NYSE was $2.31 per share. Sales of shares of our common stock under this prospectus supplement, if any, may be made by any method deemed to be an “atthe market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”).The Agents are not required to sell any specific number of shares of our common stock. The Agents have agreed to use theircommercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between the Agents The Agents will be entitled to compensation under the terms of the Sales Agreement at a commission rate equal to 3.0% of thegross proceeds of the sales price of common stock that they sell under the Sales Agreement. The net proceeds from any sales under thisprospectus supplement will be used as described under “Use of Proceeds.” The proceeds we receive from sales of our common stock, In connection with the sale of our shares of common stock on our behalf, the Agents will each be deemed to be an “underwriter”within the meaning of the Securities Act, and their compensation as Agents will be deemed to be underwriting commissions ordiscounts. We have also agreed to provide indemnification and contribution to the Agents with respect to certain liabilities, including Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on pageS-3of this prospectussupplement, as well as the documents incorporated by reference in this prospectus supplement, for a discussion of the factorsyou should carefully consider before deciding to purchase our securities. Neither the Securities and Exchange Commission Yorkville SecuritiesCanaccord GenuityNeedham & Company BMO Capital Markets The date of this prospectus supplement is December 11, 2025. Prospectus Supplement About This Prospectus SupplementProspectus Supplement SummaryRisk FactorsSpecial Note Regarding Forward-Looking Statements Prospectus About this ProspectusProspectus SummaryRisk FactorsForward-Looking StatementsUse of Proceeds ABOUT THIS PROSPECTUS SUPPLEMENT This document is in two parts. The first part is this prospectus supplement, including the documents incorporated by reference,which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documentsincorporated by reference, provides more general information. Before you invest in our securities, you should read both this prospectus Neither we nor any Agent has authorized anyone to provide you with information that is different from that contained, orincorporated by reference, in this prospectus supplement, the accompanying prospectus or in any related free writing prospectus.Neither we nor any Agent takes any responsibility for, and can provide no assurance as to the reliability of, any other information thatothers may give you. This prospectus supplement, the accompanying prospectus or any related free writing prospectus do notconstitute an offer to sell or the solicitation of an offer to buy any securities other than the securities described in this prospectussupplement or an offer to sell or the solicitation of an offer to buy such securities in any circumstances in which such offer or PROSPECTUS SUPPLEMENT SUMMARY This summary highlights selected information about us, this offering and information appearing elsewhere inthis prospectus supplement and in the documents we incorporate by reference. This summary is not complete anddoes not contain all the information you should consider before investing in our common stock pursuant to thisprospectus supplement and the accompanying prospectus. Before making an investment decision, to fully understandthis offering and its consequences to you, you should carefully read this entire prospectus supplement and theaccompanying prospectus, including “Risk Factors” beginning on pageS-3of this prospectus supplement and thefinancial statements and related notes and the other information that we incorporated by reference herein, including Compan