ESS Tech, Inc. Issues Shareholder Letter and Provides Corporate Update

Recently Appointed CEO Drew Buckley Highlights Recent Commercial Progress, Balance Sheet Actions, and Corporate Governance Updates

ESS Tech, Inc. (NYSE:GWH) (the "Company"), a leading manufacturer of long-duration energy storage systems (LDES) for commercial and utility-scale applications, today issued a letter to shareholders from Drew Buckley, Chief Executive Officer.

Dear Shareholders,

Since assuming the role of Chief Executive Officer at the beginning of 2026, my focus has been on resetting ESS Tech's leadership structure, strengthening the balance sheet, and sharpening execution as we enter the Company's next phase.

Over the past several months, we have taken deliberate steps to position the business for discipline, accountability, and long-term value creation. I want to highlight several recent developments that I believe are important as we move toward our upcoming financial reporting and investor engagements.

Leadership and Organizational Reset

Earlier this year, ESS Tech completed a comprehensive leadership transition designed to strengthen governance, execution, and financial discipline. Alongside my appointment as Chief Executive Officer, the Board appointed Kelly Goodman as Chief Strategy Officer and General Counsel and confirmed Kate Suhadolnik as Chief Financial Officer following her tenure as the Company's interim CFO.

This leadership structure reflects a renewed emphasis on execution, capital allocation, and accountability. I was also elected to the Board of Directors as a Class I director, further aligning management and Board oversight as we execute against our strategic priorities.

Recent Commercial Progress

In January, we were awarded a $9.9 million contract from Concurrent Technologies Corporation and the U.S. Air Force Research Laboratory to support the deployment of up to 27 MWh of American-made, long-duration energy storage at U.S. military installations, including the U.S. Clear Space Force Station in Alaska.

This award validates our battery technology and its ability to deliver reliable daily energy while strengthening grid resilience when it matters most. It also builds on our recent 50 MWh project with Salt River Project in Arizona and reinforces the momentum we are seeing: our technology is increasingly being selected for mission-critical infrastructure where resilience, safety, and predictable performance are required, including defense installations and data centers.

This project is expected to deploy a large-capacity iron flow energy storage system in a demanding, cold-weather environment, demonstrating durability and reliability in real-world conditions. We believe this deployment aligns with growing Department of Defense priorities around resilient, long duration microgrids that improve readiness. We are also seeing increased emphasis on "Made in USA" systems and software to reduce supply chain and cybersecurity risks. I believe that this contract can help expand our opportunity set within defense-related applications and the broader microgrid market.

We also continue to advance our Energy Base strategy, which is focused on aligning resources around scalable opportunities while completing the wind-down of legacy activities that are no longer core to our long-term objectives.

Balance Sheet Actions and Liquidity

Strengthening the balance sheet has been a key priority. In October, we closed a $40 million financing transaction that enhanced liquidity and provided additional flexibility to support operations and strategic initiatives. In November, we launched an at-the-market ("ATM") equity offering program and raised approximately $8.6 million in gross proceeds. Given our current liquidity position, sales under the program have been paused. We will continue to evaluate capital decisions with a focus on maintaining flexibility while being mindful of dilution.

Based on preliminary unaudited estimates disclosed in our recent Form 8-K, cash, cash equivalents and short-term investments as of December 31, 2025, are expected to be approximately $22 million, which does not include the $15 million registered direct offering completed after year-end. During the period, we repaid approximately $24.4 million, or 81 percent, of the $30 million under the promissory note with YA II PN, leaving approximately $5.6 million outstanding.

More recently, we completed a $15 million registered direct offering priced at $1.75, a premium to the prevailing market price. This financing strengthens our liquidity and reflects continued investor support for our strategic direction and leadership transition. On a pro forma basis, our liquidity position is meaningfully higher than the December 31 balance.

Looking Ahead

ESS enters 2026 with a reset leadership team, a strengthened balance sheet, increasing validation across commercial and defense markets, and a clearer operating focus. I believe the foundation built in 2025 across technology, manufacturing readiness, and customer engagement positions us for stronger execution and continued commercial progress.

My focus is on execution: aligning strategy, capital allocation, manufacturing scale-up, and organizational design to deliver sustainable growth and long-term shareholder value. We plan to provide an updated business outlook in the coming months, as well as deeper technology insight with an investor/analyst day at the Company headquarters in Wilsonville, Oregon in 2026.

In addition, ESS plans to participate in the upcoming ROTH Conference, taking place March 22 to 24, and look forward to engaging with investors during the event.

We appreciate the continued interest and engagement from our shareholders as we continue to move forward with a strengthened management team, improved financial position, and a clear directive. I look forward to sharing more on financial results and upcoming milestones during our fourth quarter and full year 2025 conference call, expected to be held in March.

Sincerely,

Drew Buckley

Chief Executive Officer

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.

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 expected use of the net proceeds. 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, 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-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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