ESS Tech, Inc.

Securities Trading Plans of Directors and Executive Officers

During the three months ended September 30, 2025, no director or officer, as defined in Rule 16a-1(f) under the Exchange Act, adopted orterminated a “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement,” each as defined in Regulation S-K Item 408.

Termination of Baird ATM Sales Agreement

As previously disclosed, on March 31, 2025, we entered into an at-the-market sales agreement with Baird, pursuant to which we sold 616,264 shares for total proceeds, net of commission fees, of $0.7 million. On July 11, 2025, we terminated our continuous offering under the prospectus supplement dated March 31, 2025 related to the at-the-market offering and on November 10, 2025, we delivered written notice to Baird that we were terminating the at-the-market sales agreement effective immediately. There were no termination penalties incurred by us in connection with the termination of the agreement.

Amendment of Yorkville Promissory Note

As previously disclosed, on October 14, 2025, the Company entered into an unsecured promissory note with the Investor 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. On November 12, 2025, the Company and the Investor entered into an amendment to the Promissory Note, amending the repayment schedule of the Promissory Note such that monthly payments will now begin on December 15, 2025. The Promissory Note accrues interest at a rate of 3% per annum, amortizes through maturity and matures on October 14, 2026.