ESS Tech, Inc.

Unless the context otherwise requires, all references in this Annual Report on Form 10-K to ESS, we, us, our, or the Company refer to ESS Tech, Inc. Business Combination ESS Tech, Inc. ( Legacy ESS ) was founded in 2011 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 successor legal entity. Business Overview ESS is a long-duration energy storage company specializing in iron flow battery technology. We design and produce long-duration batteries predominantly using earth-abundant materials that we believe can be cycled over 20,000 times without capacity fade based on lab-scale results. Because our batteries are designed to operate using an electrolyte of primarily salt, iron and water, our products are environmentally sustainable and substantially recyclable or reusable. Our batteries provide flexibility to grid operators and energy assurance for commercial and industrial customers. Our technology addresses energy delivery, duration and cycle-life in a single battery platform that compares favorably to lithium-ion batteries, the most widely deployed alternative technology.