Hyliion Holdings Corp. (NYSE:HYLN) ("Hyliion"), a developer of modular power plant technology, today announced that the U.S. Navy's Office of Naval Research (ONR), in partnership with the Defense Advanced Research Projects Agency (DARPA), has selected the USX-1 Defiant as a candidate test vessel for Hyliion's KARNO technology. Initial sea trials are funded under a development program from the Office of Naval Research (ONR) to advance the use of KARNO Cores for onboard power generation in U.S. Navy vessels.

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For the USX-1 Defiant sea trials, Hyliion will deliver a drop-in 800 KW power system consisting of four 200 KW KARNO Cores in a keel cooled configuration. The modular architecture is designed to demonstrate reliable, low-maintenance power generation for an unmanned vessel, where onboard servicing is not available. Trials are aimed at highlighting KARNO technology's inherent scalability and redundancy, with power units that can be distributed across the ship to support mission reliability.

The USX-1 Defiant was developed under DARPA's No Manning Required Ship (NOMARS) program, which challenged the traditional naval architecture model by designing a seaframe (the ship without mission systems) from the ground up with no provision, allowance, or expectation for humans on board. The program is part of a broader effort to modernize the U.S. Navy and optimize surface platforms for autonomous operation, enabling simpler hull designs, improved reliability and survivability, and increased flexibility in payload and power system integration. Measuring about 180 feet in length with a displacement of about 240 metric tons, USX-1 Defiant is designed for long duration autonomous operation in the open ocean, independently, or alongside other naval assets. The vessel is designed and developed by Serco-North America as a full-scale technology demonstrator and is currently undergoing sea trials.

"USX-1 Defiant represents a fundamental shift in how naval platforms are designed, powered, and operated," said Thomas Healy, Founder and Chief Executive Officer of Hyliion. "As the Navy moves toward unmanned surface vessels, power systems must be efficient, resilient, and capable of operating without human intervention. Our KARNO technology excels in these parameters, and we view USX-1 Defiant as the first of hopefully many naval platforms to be powered by this technology."

Hyliion's KARNO Core is a heat powered linear generator designed for high modularity, efficiency, and low maintenance operation, making it well suited for unmanned maritime platforms. For the U.S. Navy deployment, the KARNO Cores will operate on F-76 marine diesel and to demonstrate its ability to supply onboard power for extended durations with a low thermal and acoustic footprint. The KARNO Core generates direct current (DC) power output at 800Vdc enabling direct integration into modern ship electrical architectures. The KARNO technology is currently undergoing land-based testing and development using simulated U.S. Navy load profiles.

The views expressed are those of the author and do not reflect the official policy or position of the Department of War or the U.S. Government.

About Hyliion

Hyliion is committed to creating innovative solutions that enable clean, flexible and affordable electricity production. The Company's primary focus is to provide modular power plant technology that can operate on various fuel sources to future-proof against an ever-changing energy economy. Headquartered in Austin, Texas, and with research and development in Cincinnati, Ohio, Hyliion is initially targeting the commercial and waste management industries with a locally deployable KARNO Power Module that can offer prime power as well as energy arbitrage opportunities. Beyond stationary power, Hyliion will address mobile applications such as vehicles and marine vessels. The Company aims to offer innovative, yet practical solutions that contribute positively to the environment in the energy economy. For further information, please visit www.hyliion.com.

Forward-Looking Statements

The information in this press release includes "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of present or historical fact included in this press release, regarding Hyliion and its future financial and operational performance, as well as its strategy, future operations, estimated financial position, estimated revenues, and losses, projected costs, prospects, plans and objectives of management are forward-looking statements. When used in this press release, including any oral statements made in connection therewith, the words "could," "should," "will," "may," "believe," "anticipate," "intend," "estimate," "expect," "project," the negative of such terms and other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain such identifying words. These forward-looking statements are based on management's current expectations and assumptions about future events and are based on currently available information as to the outcome and timing of future events. Except as otherwise required by applicable law, Hyliion expressly disclaims any duty to update any forward-looking statements, all of which are expressly qualified by the statements herein, to reflect events or circumstances after the date of this press release. Hyliion cautions you that these forward-looking statements are subject to numerous risks and uncertainties, most of which are difficult to predict and many of which are beyond the control of Hyliion. These risks include, but are not limited to, our status as an early stage Company with a history of losses; our expectation of incurring significant expenses and continuing losses for the foreseeable future; our ability to develop key commercial relationships with suppliers and customers; our ability to retain the services of Thomas Healy, our Chief Executive Officer; the expected performance of the KARNO generator and system; the execution of the strategic shift from our powertrain business to our KARNO business, and the other risks and uncertainties described under the heading "Risk Factors" in our SEC filings including in our Annual Report (See item 1A. Risk Factors) on Form 10-K filed with the Securities and Exchange Commission (the "SEC") on February 25, 2026 for the year ended December 31, 2025. Given these risks and uncertainties, readers are cautioned not to place undue reliance on such forward-looking statements. Should one or more of the risks or uncertainties described in this press release occur, or should underlying assumptions prove incorrect, actual results and plans could differ materially from those expressed in any forward-looking statements. Additional information concerning these and other factors that may impact Hyliion's operations and projections can be found in its filings with the SEC. Hyliion's SEC Filings are available publicly on the SEC's website at www.sec.gov, and readers are urged to carefully review and consider the various disclosures made in such filings.

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Hyliion Holdings Corp.

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Hyliion Announces USX-1 Defiant USV as the Launch Platform for KARNO™ Core Sea Trials