American-Made, Long-Duration Iron Flow Technology Poised to Capitalize on Surging AI Data Center Power Demand and Renewable Baseload Reliability

Commercial Momentum Backed by U.S. Air Force Award, Salt River Project and Google’s Project New Horizon, VoltStorage IP Acquisition, Strengthened Capital Position, and Manufacturing Readiness

Recognized by TIME as One of America’s Top GreenTech Companies in 2025 and 2026

ESS Tech, Inc. (NYSE: GWH) ("ESS" or the "Company"), a leading manufacturer of long-duration iron flow energy storage systems (“LDES”) for commercial and utility-scale applications, has engaged international investor relations specialists MZ Group (“MZ”) to lead a comprehensive strategic investor relations and financial communications program across all key markets.

MZ will work closely with ESS management to develop and implement a comprehensive capital markets strategy designed to increase the Company's visibility throughout the investment community. The campaign will highlight ESS's differentiated position in long-duration energy storage through its American-made iron flow technology, which utilizes earth-abundant iron, salt, and water rather than lithium and other critical minerals. ESS’s solutions are designed to deliver safe, scalable, and sustainable long-duration energy storage for customers seeking greater reliability, domestic supply chain advantages, and lower total cost of ownership over a 25-year design life. As electricity demand accelerates, particularly from AI data centers, and as utilities seek long-duration storage to support baseload reliability when solar and wind are not producing, ESS believes its gigawatt-scale flagship platform Energy Base™ is well positioned to address a growing market need.

Recent milestones include a $9.9 million contract award from Concurrent Technologies Corporation and the U.S. Air Force Research Laboratory for up to 27 MWh of domestically manufactured LDES, a 50 MWh Energy Base pilot collaboration with Salt River Project (SRP) and Google under Project New Horizon at SRP's Copper Crossing facility in Florence, Arizona, and the acquisition of VoltStorage GmbH's intellectual property and assets to advance flexible long-duration storage capabilities. ESS also strengthened its capital position through a $40 million financing transaction completed in October 2025, approximately $8.6 million raised under its at-the-market equity program through March 2026, and a $15 million registered direct offering announced in January 2026 that was priced at a premium to the market. The Company’s U.S. based Wilsonville, Oregon facility has the capacity to manufacture approximately 560 MWh of batteries annually to support its Tier 1 pipeline of flagship projects, including SRP, Google, and Air Force/CTC, over the next 24 months. ESS was also recently recognized by TIME as one of America’s Top GreenTech Companies in March of 2026 and named one of Fortune's Most Innovative Companies in America 2025.

MZ has developed a distinguished reputation as a premier resource for institutional investors, brokers, analysts, and private investors and maintains offices worldwide. Chris Tyson, Executive Vice President & Partner at MZ North America, along with Director Larry Holub and Senior Associate Jack Greenberg, will advise ESS’s investor relations team in all facets of investor relations, including, but not limited to, the coordination of roadshows and investment conferences across key cities and building brand awareness with financial and social media outlets.

Chris Tyson commented, "The global energy transition is accelerating demand for long-duration energy storage, and ESS is positioned at the intersection of several of the most compelling themes in energy infrastructure today: renewable baseload power, grid reliability, domestic supply chain security, and rapidly rising electricity demand driven by AI and data centers. The Company's iron flow platform stands apart through its American-made, non-lithium chemistry, long-duration capabilities, and 25-year design life, all of which support a compelling long-term value proposition for utilities, commercial customers, and other large energy users. With recent commercial wins, an expanding pipeline, and a strengthened capital base, we believe ESS is entering an important new phase of execution and visibility. We look forward to introducing the ESS story to our network of institutional investors, family offices, and retail investors."

Drew Buckley, Chief Executive Officer of ESS Tech, commented, "We believe ESS is entering a critical execution phase as we move from technology validation toward larger-scale commercial deployment. The Energy Base platform is built for where the market is heading; long-duration, American-made energy storage designed to support renewable baseload power, improve grid resilience, and help meet the growing power needs of AI and data center infrastructure. Over the next 18 months, investors should watch several important de-risking milestones across our roadmap, including new commercial wins, pilot systems that generate data on performance and commercial viability at scale, progress on our 200 kWh and 800 kWh development path, and continued execution toward the SRP project targeted for 2027. As those milestones are achieved, we believe there may also be an opportunity to host an analyst day alongside a future pilot data release to provide the investment community with a deeper look at our technology, roadmap, and long-term market data. With a strengthened balance sheet, a refreshed leadership team, and 560 MWh of scaled manufacturing capacity in place to support recent commercial wins, we are focused on executing and converting our pipeline into revenue. We look forward to working with Chris and the entire team at MZ to share our milestones with shareholders and the broader investment community in the weeks and months ahead."

For more information on ESS, please visit www.essinc.com. To schedule a call with management, please email your request to GWH@mzgroup.us or call Chris Tyson at 949-491-8235.

About MZ

MZ North America is the US division of MZ Group, a global leader in investor relations with over 250 employees and 800 clients across 12 different exchanges. For over 25 years, MZ has implemented award-winning programs and developed a reputation for delivering tangible results for public and private companies via strategic communications, industry-leading investor outreach, public relations, a market intelligence desk, and a suite of technology solutions, spanning websites, conference call/webcasting, video production and XBRL/Edgar filing services. MZ maintains a global footprint with professionals located throughout every time zone in North America, as well as Taipei and São Paulo. For more information, please visit www.mzgroup.us.

About ESS Tech, 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.

Cautionary Language on Forward-Looking Statements

This communication contains forward-looking statements (including within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended, and Section 27A of the Securities Act of 1933, as amended) concerning the Company and other matters that involve substantial risks and uncertainties. These statements may discuss the management team’s goals, beliefs, hopes, intentions and expectations as to future plans, trends, events, results of operations and financial condition, or otherwise, based on current beliefs of the management of the Company, as well as assumptions made by, and information currently available to, the Company’s management. These forward-looking statements can be identified by the use of forward-looking terminology, including the words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intends,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “will,” “would,” or, in each case, their negative or other variations or comparable terminology may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These forward-looking statements, which are subject to risks, uncertainties and assumptions about us, may include projections of our future financial performance, our anticipated growth strategies and anticipated trends in our business. Examples of forward-looking statements include, among others, statements pertaining to statements made by the Company’s Chief Executive Officer and Chief Financial Officer, statements pertaining to the Company’s 2026 outlook and beyond, cash position, the timing of the Company’s ability to create value in the long-term, market opportunities for ESS’ products, increased pace of commercial activity, the timing for manufacturing and delivery for Project New Horizon, the timing of delivery commencing for the Company’s projects, as well as statements regarding the Company’s employees, commercial expectations regarding sales order and pipeline, the expected integration of the VoltStorage intellectual property and technology, ESS product development and manufacturing, and relationships with customers. 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, barriers we face in our attempts to produce our energy storage products; our products being in the early stage of commercialization and aspects of our technology not having been fully field tested; our inability to develop our business and effectively commercialize our energy storage products; our dependence on third-party suppliers; delays in our manufacturing operations, our ability to control our costs and achieve our cost reduction strategy; our dependence on complex machinery; our ability to increase our production capacity; required maintenance being performed incorrectly or maintenance requirements exceeding our current expectations; our history of losses; failure to deliver the benefits offered by our technology; inability to achieve market acceptance of our products; our warranty obligations; our relationships with related parties; regulatory challenges; our ability to protect our intellectual property; and our ability to raise capital in the near future; general economic and market conditions as well as geopolitical developments and other risks and uncertainties described more fully in the section titled “Risk Factors” in the Company’s Quarterly Report on Form 10-K filed on March 5, 2026, 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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