Great British Energy – Nuclear (GBE-N) has awarded a $406 million (£300 million) contract to a joint venture between Amentum (NYSE:AMTM) and Cavendish Nuclear to serve as the owner's engineer for the UK's groundbreaking small modular reactor (SMR) program.

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Contract signing - left to right: Mick Gornall, Managing Director, Cavendish Nuclear; Loren Jones, Senior Vice President, Amentum; Simon Roddy, Chief Executive Officer, Great British Energy-Nuclear; Kenny Douglas, DevCo Director, Great British Energy-Nuclear

This long-term agreement, with a maximum duration of 14 years, will support the deployment of Rolls-Royce SMR's innovative reactor technology at the Wylfa site in North Wales. The contract represents a significant milestone in advancing the UK's clean energy ambitions and the rollout of its first SMRs.

The Amentum-led joint venture, known as Litmus Nuclear, will play a pivotal role in the SMR program by delivering independent assurance and expert technical guidance across critical areas, including design, safety, engineering, construction, and commissioning. This support is designed to help GBE-N achieve its goal of securing a final investment decision for the deployment of SMRs at the Wylfa site.

"This award recognizes Amentum's expertise to accelerate the global expansion and revitalization of nuclear energy. It also underscores our central role in advancing the UK's nuclear ambitions, complementing our ongoing work at Hinkley Point C and Sizewell C," said Loren Jones, senior vice president and head of Amentum's Energy & Environment-International business. "Amentum will draw upon our expertise in nuclear science and engineering to provide independent technical and delivery assurance, helping GBE-N advance the SMR program and bolster the UK's energy security and industrial base."

The joint venture will also ensure the SMR program meets regulatory requirements and is poised to deliver reliable, low-carbon power for decades to come.

In November 2025, the UK's Department for Energy Security and Net Zero announced Wylfa, on the island of Anglesey/Ynys Môn, as the site for the country's first SMR's. These 470MWe reactors are smaller and designed to be built more quickly than some traditional nuclear power stations.

About Amentum

Amentum is a global leader in advanced engineering and innovative technology solutions, trusted by the United States and its allies to address their most significant and complex challenges in science, security and sustainability.

About Amentum in the United Kingdom

With more than 6,000 people in the UK, Amentum is the delivery partner for project and construction management services at Hinkley Point C; sole program and project management delivery partner at Sizewell C; and also supports the UK's existing nuclear power stations under a Lifetime Enterprise Agreement with EDF. It is a major supplier of engineering design, safety case and project management at Sellafield and other UK nuclear decommissioning sites and operates the country's largest private sector complex of nuclear laboratories and engineering test facilities in Warrington.

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Forward-Looking Statements

This press release contains or incorporates by reference statements by Amentum Holdings, Inc. (the "Company") that relate to future events and expectations and, as such, constitute "forward-looking statements" as that term is defined in the Private Securities Litigation Reform Act of 1995 and other federal securities laws. These forward-looking statements may be characterized by terminology such as "believe," "project," "expect," "anticipate," "estimate," "forecast," "outlook," "target," "endeavor," "seek," "predict," "intend," "strategy," "plan," "may," "could," "should," "will," "would," "will be," "will continue," "will likely result," or the negative thereof or variations thereon or similar terminology generally intended to identify forward-looking statements. All statements, other than historical facts, including, but not limited to, statements regarding the anticipated work and revenue under the awarded contract, and the Company's objectives, expectations and intentions, applicable legal, economic and regulatory conditions, and any assumptions underlying any of the foregoing, are forward-looking statements.

A number of important factors could cause actual results to differ materially from those contained in or implied by these forward-looking statements, including those factors discussed in our filings with the Securities and Exchange Commission (SEC), including, among others: the occurrence of an accident or safety incident; the ability of the Company to control costs, meet performance requirements or contractual schedules; and other factors set forth under Item 1A, Risk Factors in our Annual Report on Form 10-K for the fiscal year ended September 27, 2024, which can be found at the SEC's website at www.sec.gov or the Investor Relations portion of our website at www.amentum.com. Any forward-looking statement speaks only as of the date on which it is made, and the Company assumes no obligation to update or revise such statement, whether as a result of new information, future events or otherwise, except as required by applicable law.

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Media Contact:

Stephen Brauner

+44.7875.877120

stephen.brauner@global.amentum.com

Investor Contact:

Nathan Rutledge

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Amentum-Led Joint Venture Secures $406 Million Contract as Owner's Engineer for UK's First Small Modular Reactors