CFO — Kate Suhadolnik: The filing discloses the execution of new employment agreements for existing executives without any change in their roles, titles, or responsibilities.

Other Events. On August 20, 2026, the Company issued a press release announcing that it had priced the Offering and Concurrent Private Placement. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference. On August 21, 2026, the Company issued a press release announcing that it had closed the Offering and Concurrent Private Placement. A copy of this press release is attached hereto as Exhibit 99.2 and is incorporated herein by reference. Neither th…

Entry into a Material Definitive Agreement On August 20, 2026, ESS Tech, Inc. (the “ Company ”) entered into a securities purchase agreement (the “ Purchase Agreement ”) with certain institutional investors identified on the signature pages thereto (the “ Purchasers ”) pursuant to which the Company agreed to issue and sell in a registered direct offering registered under the Securities Act of 1933, as amended (the “ Securities Act ”), an aggregate of 6,400,000 shares (the “ Shares ”) of the C…

by reference, the Common Warrants and the Placement Agent Warrant (including the Common Stock issuable upon exercise of the Common Warrants and the Placement Agent Warrant) (collectively, the “ Private Securities ”) were issued in reliance upon the exemption from registration pursuant to Section 4(a)(2) under the Securities Act and Regulation D under the Securities Act, and corresponding provisions of state securities or “blue sky” laws. The sale of the Private Securities did not involve a pu…

shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. On July 16, 2026, ESS Tech, Inc. (the “Company”) entered into an amendment to its Sales Agreement (the “Amendment Agreement”) for its “at the market offering” program (the “ATM Program”) to sell $75 million shares of the Company’s common stock (the “Shares”) which was previously entered into with Yorkville Ives & Co., LLC (formerly Yorkville Securities, LLC) (“Yorkville Ives”), BMO Capital Markets Corp. (“BMO”), Canaccord Genuity LLC (“Canaccord”),…

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing. On June 30, 2026, the New York Stock Exchange (the “NYSE”) notified ESS Tech, Inc. (the “Company”), and, on July 1, 2026, the NYSE publicly announced that it has determined to (a) commence proceedings to delist the Company’s Public Warrants which were previously issued in connection with ACON S2 Acquisition Corp.’s initial public offering (the “Public Warrants”) (each fifteen Public Warrants i…

shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”), or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.

Director — Rich Hossfeld: Mr. Hossfeld resigned from the board of directors and Audit Committee.

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing. On June 9, 2026, ESS Tech, Inc. (the “Company”) received a written notice (the “Notice”) from the New York Stock Exchange (“NYSE”) indicating that the Company did not satisfy the continued listing standard set forth in Section 802.01C of the NYSE Listed Company Manual (“Section 802.01C”), as the average closing price of the Company’s common stock was less than $1.00 per share over a consecutiv…

and Exhibit 99.1 of this Current Report on Form 8-K shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Director — Michael Niggli: Mr. Niggli is resigning from the Board of Directors, effective as of the Company’s 2026 annual meeting.

and Exhibit 99.1 of this Current Report on Form 8-K shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement On January 29, 2026, ESS Tech, Inc. (the “Company”) signed a securities purchase agreement (the “Purchase Agreement”) with certain institutional investors identified on the signature pages thereto (the “Purchasers”) pursuant to which the Company agreed to issue and sell in a registered direct offering registered under the Securities Act of 1933, as amended (the “Securities Act”), an aggregate of 3,471,428 shares (the “Shares”) of the Company’s common…

Director (Class I member) — Drew Buckley: The CEO was elected to serve as a Class I member of the Board.

Results of Operations and Financial Condition. Preliminary Financial Results for the Year End Ended December 31, 2025 (unaudited) On January 29, 2026, ESS Tech, Inc. (the “Company”) announced that based upon preliminary estimates and information available to the Company as of the date of this Form 8-K, the Company is disclosing selected preliminary unaudited financial results for the year ended December 31, 2025: • Cash, cash equivalents and short-term investments as of December 31, 2025 are…

Chief Executive Officer — Drew Buckley: Drew Buckley, the Company’s current Head of Capital Markets Strategy, has been appointed as Chief Executive Officer.

Entry into a Material Definitive Agreement. On December 4, 2025, ESS Tech, Inc. (the “Company”) and YA II PN, LTD., an investment fund managed by Yorkville Advisors Global, L.P. (“Yorkville”), entered into Amendment No. 2 (the “Note Amendment”) to the promissory note, originally issued on October 14, 2025, and as amended on October 31, 2025 (the “First Note Amendment”), by and between the Company and Yorkville (the “Note”). Capitalized terms used but not otherwise defined herein shall have th…

Entry into a Material Definitive Agreement. On November 13, 2025, in connection with the launch of an “at the market offering” program, ESS Tech, Inc. (the “Company”) entered into a Sales Agreement (the “Sales Agreement”) with Yorkville Securities, LLC (“Yorkville”), BMO Capital Markets Corp., Canaccord Genuity LLC, Needham & Company, LLC and Stifel, Nicolaus & Company, Incorporated (the “Agents”) pursuant to which the Company may sell, from time to time, shares of the Company’s common stock,…

and Exhibit 99.1 of this Current Report on Form 8-K shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth in

Unregistered Sales of Equity Securities. The information set forth in

Entry into a Material Definitive Agreement. On October 14, 2025, ESS Tech, Inc. (the “Company”) entered into an unsecured promissory note with YA II PN, LTD., an investment fund managed by Yorkville Advisors Global, L.P. (“Yorkville”) in the aggregate principal amount of up to $40 million (the “Promissory Note”), in two tranches consisting of a first tranche of $30 million and a second tranche of $10 million, in each case less an original issue discount of 8% and certain fees and expenses. Ea…

Chief Operating Officer — Jigish Trivedi: The company appointed a new Chief Operating Officer from an external candidate.

and Exhibit 99.1 of this Current Report on Form 8-K shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.