ATI INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule

14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant To Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant ☒ Filed by a Party other than the Registrant ☐

Check the appropriate box:

ATI Inc. 2021 McKinney Avenue Dallas, TX 75201

Dear Stockholders

I am pleased to invite you to ATI’s 2025 Annual Meeting of Stockholders, my first as Chief Executive Officer and as a member of ATI’s Board of Directors.

I began my tenure as President and CEO inmid-2024, ATI’s third consecutive year of outstanding growth and market performance. We achieved important milestones during the year, delivering nearly $4.4 billion in revenue, our highest in more than a decade. We grew margins and solidified our leadership position in our core aerospace and defense markets. These high-value markets accounted for 62% of our full-year 2024 sales and reached 65% of sales for the first time in the fourth quarter of 2024, meeting our previously articulated goal and tangibly demonstrating the growing success of our strategies.

Mid-year, we announced $4 billion in new commercial aerospace sales commitments through 2040, primarily for nickel alloy products. This achievement reflects deliberate efforts to diversify our commercial aerospace portfolio; today, we are participating in every airframe and engine program across the industry. We continue to expand our presence in the defense industry, where demand for our products grows across multiple platforms, from aircraft components, to ground vehicle titanium plate, to opportunities in naval nuclear propulsion and hypersonics. We see similar demand trajectories in other keyend-markets, including electronics and specialty energy.

Simply, our customers see the benefit of our leading materials science capabilities and advanced process technologies, coupled with our demonstrated commitment to execution and operational excellence. They count on us to deliver the mission-critical materials and components they need. We are honored to be rewarded with more of their business.

We’ve also achieved significant milestones on the capital investments made to capture the growing customer demand. Titanium supply continues to be a critical issue across the aerospace and defense supply chain. We responded to our customers’ call, taking a measured, targeted approach to expanding production capacity. We brought additional melt and related capacity online during 2024 and invested in further expansion targeted for completion in 2025. At full production, this expanded capacity is expected to exceed 2022 capacity by 80%.

Complementing these efforts, in 2024 we took steps to strategically consolidate our advanced material finishing operations, creating a more competitive flow path focused on increasing production of high-value, differentiated materials. We also drove development of our new Additive Manufacturing

Products facility, which, with its commissioning early this year, bringson-line the largest format, most advanced metal additive manufacturing capabilities in the industry.

While continuing to invest for growth, we also are committed to returning capital to our shareholders. To that end, we repurchased $260 million of our outstanding stock during 2024, with $590 million remaining in our current repurchase authorization as ofyear-end.

Bottom line, our unwavering commitment to focused execution of our strategic priorities continues to drive results for our shareholders. As illustrated in this Proxy Statement, we are outpacing markets and peers in delivering stand-out returns over time. A $100 investment in ATI at the outset of 2022 is worth over $300 as of the record date for the Annual Meeting.

It is gratifying to see our team’s hard work and transformational strategies deliver meaningful shareholder value. But we’re not stopping here. There is always more to achieve. We are continuing to execute our strategies with discipline, divesting noncore assets and taking proactive steps to further improve operational efficiency and cost competitiveness.

We also fully recognize the importance of remaining nimble in the face of continuously evolving markets and prevailing geopolitical climate. I firmly believe our team is up to the challenge, remaining intently focused on our strategies and rooted in our core values. With each goal met, they strive to set the bar higher. We do what we say we’re going to do, when we say we’re going to do it, and we do it the right way. These values drive shareholder value creation and permeate our corporate governance, our approach to talent and culture, and our investor outreach.

It has been my great privilege to take the ATI helm from Bob Wetherbee, and I thank him for leading ATI’s transformation and helping create the opportunities we see on the horizon. Thank you for your support of ATI.

Notice of Annual Meeting

of Stockholders

Annual Meeting Information

DATE & TIME: Friday, May 16, 2025 11:30 a.m. Central Time

VIRTUAL MEETING SITE: www.meetnow.global/M5F5CWL

Agenda

Your vote is important Please vote as soon as possible. You can help us reduce expenses by voting your shares by telephone or Internet. How to vote

Via the internet Visit thewebsite listed on ourproxy card

By mail Sign, date and returnyour proxy card in theenclosed envelope

By telephone Call thetelephone number on yourproxy card

During the Virtual Meeting Attend the Annual Meetingwhich is being presentedvirtually via webcast and voteonline during the meeting

Admission to the Meeting

You are entitled to participate, vote and submit questions at ATI Inc.’s virtual 2025 Annual Meeting if you were a stockholder of record as of the close of business on March 17, 2025 or you hold a legal proxy for the meeting provided by your bank, broker or nominee.

Stockholders of Record. You will be able to participate in the 2025 Annual Meeting, vote electronically and submit questions during the live webcast of the meeting, without advance registration. To access the live webcast of the meeting you will need the 15-digit control number on the proxy card or the “Notice Regarding the Availability of Proxy Materials” (the “Notice”) you previously received.

Beneficial Owners. If you are a beneficial owner and hold your shares through an intermediary, such as a bank, broker, or nominee, you must register in advance to participate in the 2025 Annual Meeting, vote electronically or submit questions during the live webcast of the meeting. To register in advance, you must obtain a legal proxy from the bank, broker or other nominee that holds your shares giving you the right to vote the shares. You must forward a copy of the legal proxy, along with your email address, to Computershare Trust Company, N.A. (“Computershare”) by email atlegalproxy@computershare.com no later than 4:00 p.m. Central Time, on Tuesday, May 13, 2025. You will receive a confirmation of your registration and instructions on how to attend the meeting by email after Computershare receives your registration materials.

Beneficial owners that are unable to register in advance may still attend the 2025 Annual Meeting by visitingwww.meetnow.global/M5F5CWLas a “guest” but will not have the option to vote shares electronically or submit questions during the live webcast of the meeting. However, you may submit questions in advance of the meeting by emailing your question, along with proof of ownership, to investors@ATlmaterials.com.

Our Proxy Statement and 2024 Annual Report are available for review by stockholders of record atenvisionreports.com/ATI and by beneficial owners atedocumentreview.com/ATI. For further information about ATI, please visit our website atatimaterials.com. This Proxy Statement is first being provided to our stockholders on or about March 27, 2025.

On behalf of the Board of Directors:

March 27, 2025

Important notice regarding the availability of proxy materials for the ATI Annual Meeting of Stockholders to be held on Friday, May 16, 2025.

As permitted under applicable Securities and Exchange Commission (“SEC”) rules, we are mailing our stockholders a Notice of Internet Availability of Proxy Materials containing instructions on how to access our proxy materials and submit proxy votes online. Our Proxy Statement, proxy card and 2024 Annual Report are available for review at: envisionreports.com/ATI.