Amentum Holdings, Inc.

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PROXY STATEMENT SUMMARY

This summary highlights certain information contained elsewhere in this proxy statement. The summary does not contain all of the information that you should consider, and you should review our Annual Report on Form 10-K for the fiscal year ended October 3, 2025 (the “Annual Report”) and the entire proxy statement carefully before voting.

Unless the context otherwise indicates or requires, as used in this proxy statement, references to: (i) “Amentum,” the “Company,” “we,” “us,” “our,” or our “company” refer to Amentum Holdings, Inc., its consolidated subsidiaries and predecessors; (ii) “our Board” or “the Board” means the Board of Directors of the Company; (iii) “stockholder” means holders of our common stock; (iv) “fiscal,” refers to our fiscal years ended the closest Friday to September 30; and (v) “you,” “your,” “yours,” or other words of similar import in this proxy statement refers to stockholders entitled to vote on the matters to be presented at the 2026 Annual Meeting of Stockholders (the “Annual Meeting”).

2026 Annual Meeting of Stockholders

Voting Matters and Board Recommendations

Stockholders are being asked to vote on the following matters at the 2026 Annual Meeting of Stockholders:

How to Vote

Stockholders as of the record date may vote electronically at the virtual meeting or vote in advance by submitting a proxy by Internet, telephone, or mail as follows:

Background on the Transaction that Created Amentum

On September 27, 2024, Amentum became a public company through the consummation of the spin-off of Jacobs Solutions Inc.’s (“Jacobs”) Critical Missions Solutions business and portions of Jacobs’ Divergent Solutions business (together, the “CMS Business”) and merger with Amentum Parent Holdings LLC (including its affiliates and subsidiaries, “Legacy Amentum”) in a tax-efficient Reverse Morris Trust transaction (collectively, the “Transaction”). Prior to the spin-off, the CMS Business reorganized under a newly formed company named Amazon Holdco Inc. (“CMS”) and distributed a $911 million cash dividend payment to Jacobs, who then distributed prior to the merger approximately 80.95% of the outstanding shares of CMS common stock on a pro rata basis to Jacobs’ shareholders. In connection with the completion of the merger, CMS was renamed Amentum Holdings, Inc. On September 30, 2024, Amentum began trading on the New York Stock Exchange under the ticker symbol “AMTM”.

Amentum’s governance is subject to the provisions of our amended and restated certificate of incorporation, our amended and restated bylaws, and a stockholders agreement that Amentum entered into with Amentum Joint Venture L.P. (the former owner of Amentum Parent Holdings LLC; hereinafter “Amentum Equityholder” and including, where relevant, Sponsor Stockholder as defined below) in connection with the Transaction (the “Stockholders Agreement”). The key provisions in these documents relating to the governance of Amentum are summarized in the information statement filed as Exhibit 99.1 to the Current Report on Form 8-K of Amazon Holdco Inc. (now known as Amentum Holdings, Inc.), filed with the Securities and Exchange Commission (the “SEC”) on September 18, 2024 (the “Information Statement”).

Company Performance and Highlights

Performance highlights from Amentum’s fiscal year 2025 include:1

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Annual Revenues of $14.4 billion, 4% growth on a pro forma basis

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Annual Net Income of $66 million; Annual Adjusted EBITDA of $1,104 million

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Annual Diluted Earnings Per Share of $0.27; Annual Adjusted Diluted Earnings Per Share of $2.22

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Annual Operating Cash Flow of $543 million; Annual Free Cash Flow of $516 million

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Backlog of $47 billion; Book-to-Bill — 1.6x Fourth Quarter, 1.2x Full Year

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Reduced Net Debt to $3.6 billion and Net Leverage to 3.2x

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Successful first year as a newly merged public company; exceeded mid-point of financial guidance and achieved key integration milestones

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The proxy statement includes the presentation and discussion of Adjusted EBITDA and Adjusted EBITDA Margin, which are not measures of financial performance under Generally Accepted Accounting Principles in the United States (“GAAP”). Non-GAAP financial measures should be considered in addition to, but not as a substitute for, the information provided in accordance with GAAP. Management believes that these non-GAAP measures provide another measure of Amentum’s results of operations and financial condition, including its ability to comply with financial covenants. See Unaudited Non-GAAP Financial Measures in Appendix A for more information and a reconciliation of our selected reported results to these non-GAAP measures.

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Our Board of Directors

Each of our directors is elected by our stockholders on an annual basis to serve until the next annual meeting and until their respective successors are elected and qualified, or until such director’s earlier death, resignation or removal. Each of our current directors has been nominated for election to the Board, and you can find additional information regarding our Board nominees under “Proposal 1: Election of Directors” beginning on page 6.

Our board of directors consists of 13 members and reflects a range of ages, with three directors between ages 35 and 55, six directors between ages 56 and 67, and four directors between ages 68 and 78. Three of the directors identify themselves as women and one as African American.

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Executive Chair

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Chief Executive Officer

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Lead Independent Director

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Corporate Governance Highlights

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Eleven of our thirteen directors are independent.

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The Audit, Compensation, and Nominating and Governance Committees are composed entirely of independent directors.

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Our directors serve one-year terms and stand for election annually.

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We provide for a majority voting standard in our bylaws for the election of directors in uncontested elections and a plurality voting standard for the election of directors in contested elections.

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We do not have a “poison pill” in effect.

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The Board of Directors holds regular executive sessions of independent directors.

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We conduct annual Board and committee evaluations and self-assessments.

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Our policy on public company board service helps to ensure a director’s ability to devote necessary time to Board duties.

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Our Board of Directors and senior leadership exercise oversight in respect of corporate-wide matters, including enterprise risk management and sustainability.

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The Board of Directors conducts an annual discussion on management succession planning, with support provided by the Nominating and Governance Committee.

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We adhere to robust executive officer and director stock ownership guidelines.

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Our policies prohibit short sales, frequent trading, and derivative transactions in our equity, as well as hedging, pledging and the use of margin accounts.

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Our policies include a provision for the recoupment from executives of equity-based compensation in the event of misconduct leading to a financial restatement.

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Our Investor Relations team and management regularly engage with current and potential stockholders.

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Executive Compensation Highlights

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We foster alignment between pay and performance (both company success and shareholder value).

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We emphasize variable pay (short- and long-term incentives) over fixed pay (salary).

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We emphasize long-term versus short-term pay.

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We require our executives and directors to satisfy meaningful stock ownership requirements.

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We ensure an appropriate peer group to benchmark executive compensation.

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We review on a regular basis our executive talent, performance, deployments, and succession.

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We evaluate policies and programs on a regular basis to ensure competitiveness and alignment to organizational goals.

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We limit excessive compensation for executives by setting compensation caps and restricting excessive perks and non-monetary benefits.

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Additional details about our executive compensation philosophy and structure can be found in the Compensation Discussion and Analysis (“CD&A”), starting on page 42.

Sustainability Discussion and Highlights

Our approach to sustainability takes the core elements of our corporate values and instills them into our business strategy with the purpose of challenging convention and driving progress to bring solutions to the most significant challenges in science, security and sustainability. Doing so provides an advantage that benefits our shareholders, employees, customers, and the communities where we live and serve.

To advance our initiatives around sustainability, we have devised a plan of governance through the Nominating and Governance Committee of our Board having oversight of the Company’s sustainability strategy. To facilitate the strategy, Amentum established a Sustainability Lead to delineate clear pathways around the Company’s related efforts. With support and backing from cross-functional leaders around the enterprise, each holding operational or policy-level responsibility for an area of performance that relates to our sustainability priorities, the Sustainability Lead serves as an advisory body to our Executive Leadership Team on sustainability matters.

We released our 2024 Impact Report in July 2025. The 2024 Impact report reflected pre-Transaction actions and included information from both the Legacy Amentum and CMS businesses. Our next step will be to issue our Impact Report in 2026 to reflect post-closing operations as a public company, adhering to regulations and following guidelines and reporting frameworks applicable to our Company and industry.

Human Capital Management

Our team of experienced senior executives leads Amentum with a history of developing, engineering and delivering complex technical and management solutions to a broad base of U.S. and allied government agencies, and customers in international and commercial markets. With significant experience in relevant industries or roles, this team is respected by customers, business partners and employees for their technical expertise across the defense, security, intelligence, energy and environmental markets. Recognized for their ethical behavior, focus on employee safety, commitment to collaboration, and personal embrace of Amentum’s core values, they lead by example in support of their leadership brand.

Our team is focused on delivering purpose-driven solutions. We hold ourselves accountable to our team, customers, company, and communities and innovate as a team passionate about making a difference in an ever-changing world. Our culture and values embrace collaboration, which serve as a beacon for sharing our continued success and experience with all our customers’ missions.

We have created a values-driven culture by fostering a sense of belonging, welcoming all perspectives and contributions, and providing equal access to opportunities and resources for everyone. Our high-performing culture supports a best-in-class employee experience. In combination, our ethics and compliance program, high-performing culture, and core values provide our workforce with clarity on what is expected to be successful as an Amentum employee.

Amentum has approximately 50,000 employees, which excludes employees of our joint ventures. These personnel are assigned across all 50 states and in over 70 countries.

A significant portion of Amentum’s workforce is made up of veterans who served in our nation’s armed forces. Our employees, both domestic and international, are deeply embedded in our customer missions in positions of trust, as more than 50% of our employees hold either a special access or security clearance.