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 29, 2024, including the sections titled “Forward Looking Statements” and “Risk Factors” for a description of 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 and critical applications in electronics, medical and 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.

2024 PERFORMANCE

We believe that the strategic and operational changes we have achieved in recent years and continue to pursue are positioning our business for success in 2025 and beyond, and critically, are driving our ability create shareholder value. The following charts illustrate ATI’s relative total shareholder return (“TSR”) compared to the S&P 500 in 2024 and since the beginning of 2022:

WHAT’S NEW

Among many recent achievements and changes driving further growth, value creation and shareholder return, during 2024: ◆ Kimberly A. Fields became President and CEO in July, and Robert S. Wetherbee became Executive Chairman ◆ Ms. Fields was appointed to our Board, with women now comprising 40% of our Board ◆ Vaishali S. Bhatia joined our executive leadership as Senior Vice President, General Counsel and Chief Compliance Officer ◆ Aerospace and defense accounted for 65% of sales by the fourth quarter ◆ We returned $260 million to stockholders through our share repurchase program, ending the year with an additional $590 million inremaining repurchase authority

PROPOSAL 1: ELECTION OF OUR DIRECTOR NOMINEES

At the Annual Meeting, Class II directors Leroy M. Ball, Carolyn Corvi and Robert S. Wetherbee will stand for re-election to a three-year term.

ATI has a diverse, highly credentialed and highly experienced Board. Our directors, with their variety of tenure, qualifications, backgrounds, skills and experiences contributing 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

Our commitment to strong corporate governance is further illustrated by the following practices:

PROPOSAL 2: 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. The goals of our program are to compensate executive management based on performance, create long-term stockholder value and attract and retain key employees. A significant portion of the target compensation of our CEO, our Executive Chairman (former CEO) and each of our other NEOs is subject to the achievement of rigorous performance goals and, as the following charts illustrate, is therefore “at risk.” 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 both our 2023 and 2024 Annual Meetings.

2024 Target Pay Mix

When making determinations and awards under our incentive plans, the Compensation and Leadership Development Committee considers both target compensation and the actual dollar value of awards to be delivered to the NEOs in any given year, as illustrated by the Total Realized Compensation figures below. The compensation our named executive officers earned in 2024, when our business achieved significant milestones, is directly linked to the value delivered by the ongoing success of our long-term strategies.

2024 Target Annual Compensation Comparison to Total Realized Compensation

• Elliot S. Davis, who also qualified as a NEO for 2024, retired in October 2024. His 2024 target compensation was $1,905,500. For more information about Mr. Davis’s compensation, see our discussion of Executive Compensation beginning on page 40. For additional discussion regarding year-over-year trends in total realized compensation and an explanation of how total realized compensation is calculated, see page 56.

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 2025. Our Audit and Risk Committee actively monitors our independent auditor firm’s work and relationships to confirm their ongoing independence and limit their services to audit and audit-related matters.