ATI INC

This summary highlights information that is contained elsewhere in this Proxy Statement. You should carefully read this Proxy Statement in its entirety before voting, as this summary does not contain all of the information that you should consider. For more complete information regarding our business and its recent financial performance, you should review our Annual Report on Form 10-K for the fiscal year ended December 28, 2025, including the sections titled “Forward Looking Statements” and “Risk Factors”, which describe the risks and uncertainties related to any forward-looking statements included in this Proxy Statement.

ANNUAL MEETING OF STOCKHOLDERS

MEETING AGENDA

ABOUT ATI

ATI is a global producer of high-performance materials and solutions for the global aerospace and defense markets, with emerging opportunities for specialty energy. We’re solving the world’s most difficult challenges through materials science. We partner with our customers to deliver extraordinary materials that enable their greatest achievements: their products fly higher and faster, burn hotter, dive deeper, stand stronger and last longer. Our proprietary process technologies, unique customer partnerships, and commitment to innovation deliver materials and solutions for today and the evermore challenging environments of tomorrow.

2025 PERFORMANCE

We believe that the strategic and operational milestones we have achieved in recent years, and the targets we continue to pursue, are driving shareholder value creation and positioning our business for success in 2026 and beyond. The following charts illustrate ATI’s relative total shareholder return (“TSR”) compared to the S&P 500 in 2025 and since the beginning of 2023:

WHAT’S NEW

During 2025: ◆ Kimberly A. Fields, ATI’s President and Chief Executive Officer, was appointed to succeed Robert S. Wetherbee as Board Chair ◆ Two new independent directors with deep aerospace experience, Elizabeth H. Lund and Jean Lydon-Rodgers, joined our Board ◆ Leroy M. Ball was appointed to succeed J. Brett Harvey as Lead Independent Director ◆ James Robert Foster was appointed to succeed Donald P. Newman as Chief Financial Officer, effective January 1, 2026 ◆ Aerospace and defense accounted for 68% of full-year sales ◆ We returned $470 million to stockholders through our share repurchase program and saw our stock price more than double

PROPOSAL 1: ELECTION OF OUR DIRECTOR NOMINEES

At the Annual Meeting, Class III directors Kimberly A. Fields, Elizabeth H. Lund and David J. Morehouse each will stand forre-election to a three-year term. J. Brett Harvey and Robert S. Wetherbee will retire from our Board effective at the conclusion of the Annual Meeting.

ATI has a diverse, highly credentialed and highly experienced Board. Our directors, with their variety of tenure, qualifications, backgrounds, skills and experience contribute to a Board that is well-rounded and well-positioned to effectively oversee our business and promote the interests of our stakeholders.

Highly Engaged Board Oversees Risk and Guides the Strategic Direction of Our Company

The ATI Board:

*Excludes Brett Harvey and Robert Wetherbee, both of whom will retire from the Board at the conclusion of the Annual Meeting.

Continuing Director Skills and Experience Matrix

PROPOSAL 2: APPROVAL OF OUR EXECUTIVE OFFICER COMPENSATION

At the Annual Meeting, our stockholders will be asked to approve the compensation of our named executive officers (our “NEOs”) on anon-binding advisory basis. ATI’s executive compensation program is designed to support our long-term strategic vision and to align with ourpay-for-performance philosophy. Our Compensation and Leadership Development Committee believes our executive compensation program should:

We believe that our compensation program is easy to understand, performance-driven and appropriately aligned with stockholders’ interests. Our program:

As the following charts illustrate, significant portion of the target compensation of our CEO and each of our other NEOs is subject to the achievement of rigorous performance goals and is therefore “at risk.”

2025 Target Pay Mix

Reflecting this clear commitment to paying for performance, our executive compensation programs garner strong stockholder support. Our Say on Pay proposals were overwhelmingly approved by more than 98% of the shares voted at our 2023, 2024 and 2025 Annual Meetings.

PROPOSAL 3: AUDITOR RATIFICATION

At the Annual Meeting, our stockholders will be asked to ratify the appointment of Ernst & Young LLP as our independent auditor for 2026. Our Audit and Risk Committee actively monitors our independent audit firm’s work and relationships to confirm their ongoing independence and to limit their services to audit and audit-related matters.