ESS Tech Inc美股招股说明书(2025-10-22版)

619,694 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated October 14, 2025, the prospectus supplement datedJuly 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we areoffering 619,694 shares of our common stock to YA II PN, Ltd., a Cayman Islands exempt limited partnership (“Yorkville”), at a priceof approximately $4.95 per share, pursuant to our previously announcedStandby Equity Purchase Agreement with Yorkville datedJuly 9, 2025 (the “SEPA”). These shares are being issued as part of the commitment by Yorkville to purchase from time to time sharesof our common stock pursuant to the SEPA. The total purchase price of the shares is approximately $3,053,016. We used 80% of theproceeds from the issuance of the shares in this offering to repay a portion of the principal amount owed to Yorkville pursuant to anoutstanding promissory note. We intend to use the additional net proceeds to continue normal business operations related to ourstrategic pivot focused on the Energy Base product and ongoing contracting activities. We issued the shares to Yorkville onOctober22, 2025. In addition to our issuance of our shares to Yorkville pursuant to the SEPA, this Prospectus also covers the resale of these sharesby Yorkville to the public. Though we have been advised by Yorkville, and Yorkville represents in the SEPA, that Yorkville ispurchasing the shares for its own account, for investment purposes in which it takes investment risk (including, without limitation, therisk of loss), and without any view or intention to distribute such shares in violation of the Securities Act of 1933, as amended (the“Securities Act”), or any other applicable securities laws, the Securities and Exchange Commission (the “SEC”) may take the positionthat Yorkville may be deemed an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act and any profits on thesales of shares of our common stock by Yorkville and any discounts, commissions or concessions received by Yorkville are deemed tobe underwriting discounts and commissions under the Securities Act. For additional information on the methods of sale that may beused by Yorkville, see the section entitled “Plan of Distribution” on page S-12 of the prospectus supplement dated July 11, 2025 andpage 33 of the base prospectus dated November 17, 2022. Our shares of common stock are listed on the NYSE under the symbol “GWH.” On October22, 2025, the closing sale price of ourcommon stock was $4.84 per share. We are an “emerging growth company” and a “smaller reporting company” under federalsecurities laws and, as such, are subject to reduced public company reporting requirements. Investing in our common stock involves risks. Please read “Risk Factors,” beginning on page S-6 of the prospectussupplement dated July 11, 2025. Neither the SEC nor any other regulatory body has approved or disapproved of these securities or passed upon theaccuracy or adequacy of the Prospectus. Any representation to the contrary is a criminal offense. The date of this prospectus supplement is October22, 2025. Neither we nor Yorkville have authorized anyone to provide you with any information other than the informationcontained in or incorporated by reference in this prospectus supplement or the Prospectus and in the documents incorporatedby reference herein and therein. We and Yorkville take no responsibility for, and can provide no assurance as to the reliabilityof, any other information that others may give you. We are not making an offer of these securities in any state or jurisdictionwhere the offer is not permitted. You should assume that the information contained in or incorporated by reference in thisprospectus supplement or the Prospectus is accurate only as of their respective dates. The Offering 619,694 shares of common stock of ESS Tech, Inc. Securities offeredCommon stockoutstanding after theofferingPurchaserPurchase priceProceedsUse of proceeds 19,617,070 YA II PN, Ltd. pursuant to the Standby Equity Purchase Agreement dated July 9, 2025 Approximately $4.95 per share Approximately $3,053,016 We used 80% of the proceeds from the issuance of the shares in this offering to repay a portion of theprincipal amount owed to Yorkville pursuant to an outstanding promissory note. We intend to use theadditional net proceeds to continue normal business operations related to our strategic pivot focused onthe Energy Base product and ongoing contracting activities. See “Use of Proceeds” on page S-11 in ourprospectus supplement dated July 11, 2025. Symbol for our commonstock “GWH” This prospectus supplement, the prospectus supplement dated October 14, 2025, the prospectussupplement dated July 11, 2025 and the base prospectus dated November 17, 2022 also cover the resaleof shares by YA II PN, Ltd. to the public. See “Plan of Distribution” on page S-12 in our prospectussupplement dated July