Project to Deploy up to 27 MWh American-Made Large Capacity Energy Storage (LCES) System at U.S. Clear Space Force Station in Alaska

ESS Tech, Inc. ("ESS," "ESS, Inc." or the "Company") (NYSE:GWH), a leading manufacturer of long-duration energy storage systems (LDES) for commercial and utility-scale applications, today announced the execution of a $9.9 million contract with Concurrent Technologies Corporation ("CTC") and the United States Air Force Research Laboratory ("AFRL") for a large capacity energy storage (LCES) system at the U.S. Clear Space Force Station in Alaska.

The Air Force Research Laboratory is the primary scientific research and development center for the Department of the Air Force. AFRL plays an integral role in leading the discovery, development, and integration of affordable warfighting technologies for its air, space, and cyberspace force. The prime contractor, Concurrent Technologies Corporation, is an independent, nonprofit, applied scientific research and development professional services organization, and provides comprehensive energy and sustainability solutions for military installations.

Under the contract, ESS will deploy up to 27 MWh of its American-made iron flow battery (IFB) systems to support operations at Clear Space Force Station in Alaska. The project is part of an AFRL initiative to demonstrate new and emerging advanced energy storage and energy efficiency technologies capable of meeting demanding military requirements in some of the harshest environments on earth, including temperatures below -40°C. ESS's iron flow battery technology will integrate with microgrids, advanced controls and complementary systems to optimize energy use and provide continuous, reliable power for mission critical operations at the station.

"This project is a significant validation of ESS battery technology and its ability to provide reliable energy every day and support grid resiliency when it matters most," said Drew Buckley, Chief Executive Officer of ESS. "Building on our recent 50 MWh project for Salt River Project in Arizona, our technology is being chosen for essential grid resilience capabilities and optimized energy consumption at mission-critical infrastructure including defense installations and data centers.

"The Department of Defense is actively seeking long duration resilient microgrids to improve readiness, with a keen interest in ‘Made in USA' software and systems to reduce risk of foreign cyber security vulnerabilities. We believe this award will further unlock long duration storage opportunities with the DoD and the growing microgrid market," concluded Buckley.

Kevin Merichko, Director, Infrastructure at CTC added, "By enabling localized power (islanding), rapid recovery and a stable electricity supply during grid instability or disruptions, resilient grids help avert severe safety, operational and financial consequences while assuring critical missions continue without interruption. We look forward to working with ESS, AFRL and the U.S. Space Force, to further improve Clear Space Force Station resilience."

About ESS, Inc.

ESS (NYSE:GWH) is the leading manufacturer of long-duration iron flow energy storage solutions. ESS was established in 2011 with a mission to accelerate decarbonization safely and sustainably through longer lasting energy storage. Using easy-to-source iron, salt, and water, ESS iron flow technology enables energy security, reliability and resilience. We build flexible storage solutions that allow our customers to meet increasing energy demand without power disruptions and maximize the value potential of excess energy. For more information visit www.essinc.com.

Forward-Looking Statements

This communication contains certain forward-looking statements, including statements regarding ESS and its management team's expectations, hopes, beliefs, intentions or strategies regarding the future. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intends," "may," "might," "plan," "possible," "potential," "predict," "project," "should," "will," "would" and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Examples of forward-looking statements include, among others, statements regarding the Company's productization and manufacturing plans, the timing of delivery and commercialization of the Company's Energy Base projects, the ability of the Company to scale, grow, strengthen partnerships and provide long-term value, the status of customer projects and contracts, and statements by the Company's Chief Executive Officer. These forward-looking statements are based on ESS' current expectations and beliefs concerning future developments and their potential effects on ESS. Many factors could cause actual future events to differ materially from the forward-looking statements in this communication. There can be no assurance that the future developments affecting ESS will be those that we have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond ESS control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements, which include, but are not limited to, delays, disruptions, or quality control problems in the Company's manufacturing operations; issues related to the development and launch of the Energy Base product; failure to successfully bid on projects and acquire customers; issues related to the Company's partnerships with third parties; risk of loss of government funding for customer projects; failure to raise additional capital, on acceptable terms or at all; and other risks and uncertainties described more fully in the section titled "Risk Factors" in the Company's Quarterly Report on Form 10-Q filed on November 13, 2025, and the Company's other filings with the U.S. Securities and Exchange Commission. Except as required by law, ESS is not undertaking any obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise.

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ESS Tech Awarded $9.9 Million Contract from Concurrent Technologies Corporation and U.S. Air Force Research Laboratory