Business Description

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND CONSOLIDATION, AND RISKS AND UNCERTAINTIES Description of Business —ESS Tech, Inc. (“ESS” or the “Company”) is a long-duration energy storage company specializing in iron flow battery technology. ESS develops long-duration iron flow batteries for commercial and utility-scale energy storage applications requiring up to twelve hours of flexible energy capacity predominantly using earth-abundant materials. The Company was founded in 2011 (“Legacy ESS”) and became a publicly traded company through a business combination with a special purpose acquisition company named ACON S2 Acquisition Corp. (“STWO”) which changed its name to ESS Tech, Inc. upon closing (the “Business Combination”). As a result of the Business Combination, Legacy ESS survived and became a wholly owned subsidiary of ESS Tech, Inc. On March 31, 2024, Legacy ESS merged with ESS Tech, Inc. leaving ESS Tech, Inc. as the sole remaining legal entity. Basis of Presentation —The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Basis and Principles of Consolidation —The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Project New Horizon, LLC, which was formed in October of 2025 and is wholly owned and controlled by the Company. The subsidiary and its activity is immaterial to the results and financial position of the Company as of December 31, 2025. All intercompany accounts and transactions have been eliminated upon consolidation. Risks and Uncertainties —The Company is subject to a number of risks associated with companies of similar size in its industry, including, but not limited to, the need for successful development of products, the need for additional capital and financing to fund…