Free Writing Prospectus (Form FWP)

Filed Pursuant to Rule 433

Registration Statement No. 333-277308

June 3, 2026

Pricing Term Sheet

ATI Inc.

$450,000,000 5.875% Senior Notes due 2033

This term sheet to the preliminary prospectus supplement dated June 3, 2026 should be read together with the preliminary prospectus supplement before making a decision in connection with an investment in the securities. The information in this term sheet supersedes the information contained in the preliminary prospectus supplement to the extent that it is inconsistent therewith. Terms used but not defined herein have the meaning ascribed to them in the preliminary prospectus supplement.

We expect that delivery of the Notes will be made to investors on or about June 8, 2026, which will be the third business day following the date of the final prospectus supplement (such settlement being referred to as "T+3"). Under Rule 15c6-1 under the Securities Exchange Act of 1934, as amended, trades in the secondary market are required to settle in one business day, unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the Notes prior to one business day before delivery will be required, by virtue of the fact that the notes initially settle in T+3, to specify an alternate settlement arrangement at the time of any such trade to prevent a failed settlement. Purchasers of the Notes who wish to trade the Notes prior to their date of delivery hereunder should consult their advisors.

The Issuer has filed a registration statement (including a preliminary prospectus supplement) with the SEC for the offering to which this communication relates. Before you invest, you should read the preliminary prospectus supplement included in that registration statement and other documents we have filed with the SEC for more complete information about us and this offering. You may get these documents for free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, we or the underwriters will arrange to send you the prospectus if you request it by calling Goldman Sachs & Co. LLC toll-free at (866) 471-2526.

Any legends, disclaimers or other notices that may appear below are not applicable to this communication and should be disregarded. Such legends, disclaimers or other notices have been automatically generated as a result of this communication having been sent via Bloomberg or another email system.