ATI / ATI Inc. - Pengajuan SECLaporan Tahunan, Pernyataan Proksi

Second Amended and Restated Revolving Credit, Term Loan, Delayed Draw Term Loan and Security Agreement, dated as of June 13, 2025, by and among the Borrowers party thereto, the Company and other Guarantors party thereto, the Lenders party thereto and PNC Bank, National Association, as Lender and Agent (filed herewith).*

Exhibit 10.1 SECOND AMENDED AND RESTATED REVOLVING CREDIT, TERM LOAN, DELAYED DRAW TERM LOAN AND SECURITY AGREEMENT by and among OREGON METALLURGICAL, LLC, ALLEGHENY LUDLUM, LLC, TDY INDUSTRIES, LLC, INTERNATIONAL HEARTH MELTING, LLC, ATI PRECISION FINISHING, LLC, TITANIUM WIRE CORPORATION, ENVIRONMENTAL, INC., ATI TITANIUM LLC, ATI LADISH LLC, ATI LADISH MACHINING, INC., CHEN-TECH INDUSTRIES, INC

ATI Announces Second Quarter 2025 Results Continued year-over-year sales growth driven by aerospace & defense Aerospace and defense sales of $762 million, representing 67% of Q2 2025 sales Strong demand for commercial jet engines - YoY sales growth o

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Second Quarter 2025 Results Continued year-over-year sales growth driven by aerospace & defense Aerospace and defense sa

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 29, 2025 ☐ TRANSITION REPORT PURSUANT TO S

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 29, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): July 31, 2025 ATI Inc. (Exact name

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): July 31, 2025 ATI Inc.

ATI Inc.

CORRESP ATI Inc. 2021 McKinney Avenue Suite 1100 Dallas, TX 75201 www.ATImaterials.com June 20, 2025 United States Securities and Exchange Commission Division of Corporation Finance Office of Manufacturing 100 F Street, N.E. Washington, D.C. 20549 Attention: Claire Erlanger Re: ATI Inc. Form 10-K for the Fiscal Year Ended December 29, 2024 Form 8-K furnished February 4, 2025 File No. 001-12001 Lad

Entry into a Material Definitive Agreement, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 20, 2025 (June 13, 2025) ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2024 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2024 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc. (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commis

SD UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc.

Current Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 21, 2025 (May 15, 2025) ATI Inc.

Fifth Amended and Restated Bylaws

Exhibit 3.1 ATI INC. FIFTH AMENDED AND RESTATED BYLAWS Dated as of May 16, 2025 TABLE OF CONTENTS Page ARTICLE I OFFICES 1 Section 1. Registered Office 1 Section 2. Offices 1 ARTICLE II MEETINGS OF STOCKHOLDERS 1 Section 1. Place of Meetings 1 Section 2. Annual Meeting 1 Section 3. Special Meetings 4 Section 4. Notice of Meetings; Waiver 4 Section 5. Quorum; Adjournment 5 Section 6. Proxies and Vo

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 1, 2025 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 30, 2025 ☐ TRANSITION REPORT PURSUANT TO

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 30, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

ATI Announces First Quarter 2025 Results Strong year-over-year sales growth driven by aerospace & defense Aerospace and defense sales of $754 million, representing 66% of Q1 2025 sales Agreement with USW for Specialty Rolled Products employees ratifi

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces First Quarter 2025 Results Strong year-over-year sales growth driven by aerospace & defense Aerospace and defense sales

ATI Inc.

CORRESP ATI Inc. 2021 McKinney Avenue Suite 1100 Dallas, TX 75201 www.ATImaterials.com April 22, 2025 United States Securities and Exchange Commission Division of Corporation Finance Office of Manufacturing 100 F Street, N.E. Washington, D.C. 20549 Attention: Claire Erlanger Re: ATI Inc. Form 10-K for the Fiscal Year Ended December 29, 2024 Form 8-K furnished February 4, 2025 File No. 001-12001 La

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

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: ☐ Preliminary Proxy Statement ☐ Confidential, for

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

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: ☐ Preliminary Proxy Statement ☐ Confidential, for

Form of 2025 Time-Vested Restricted Stock Unit Agreement (filed herewith)*

Exhibit 10.17 Form of 2025 Time-Vested Restricted Stock Unit Agreement This Time-Vested Restricted Stock Unit Agreement (“Agreement”) is made as of the 3rd day of January, 2025 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated 2022 Incentive Plan (the “Incentiv

Insider Trading Policy (filed herewith).

Exhibit 19.1 ATI Inc. Insider Trading Policies and Procedures (as of February 2025) These Insider Trading Policies and Procedures outline the standards of ATI Inc. (“ATI” or the “Company”) on trading and causing the trading of the Company’s securities or securities of other publicly-traded companies while in possession of confidential information. This policy is divided into two parts. The first p

Form of 2025 Performance-Vested Restricted Stock Unit Agreement (filed herewith)*

Exhibit 10.18 Form of 2025 Performance-Vested Restricted Stock Unit Agreement This Performance-Vested Restricted Stock Unit Agreement (this “Agreement”) is made as of the 3rd day of January, 2025 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated 2022 Incentive

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 29, 2024 OR ☐ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission file number 1-12001 ATI Inc. (Exact n

Subsidiaries of the Registrant (filed herewith).

Exhibit 21.1 SUBSIDIARIES OF THE REGISTRANT The following lists the subsidiaries of ATI Inc., excluding those subsidiaries which, considered in the aggregate as a single subsidiary, do not constitute a significant subsidiary. Name of Subsidiary State or Country of Incorporation Allegheny Ludlum, LLC Pennsylvania ATI Specialty Rolled Products Holdings LLC Pennsylvania ATI Ladish LLC Wisconsin ATI O

ATI Announces Fourth Quarter 2024 Results Full year 2024 sales of $4.4 billion represents ATI's highest total since 2012

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Fourth Quarter 2024 Results Full year 2024 sales of $4.4 billion represents ATI's highest total since 2012 ◦Q4 2024 sale

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 4, 2025 ATI Inc. (Exact na

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 4, 2025 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 29, 2024 ☐ TRANSITION REPORT PURSUANT

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 29, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact nam

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 29, 2024 ATI Inc.

Amended Executive Severance Plan (filed herewith)*

Exhibit 10.1 ATI INC. AMENDED EXECUTIVE SEVERANCE BENEFIT PLAN Adopted September 19, 2024 ARTICLE I NAME, PURPOSE AND EFFECTIVE DATE OF PLAN 1.1 Name of the Plan. ATI Inc. (together with its Subsidiaries, as defined in this Plan, the “Company”) hereby establishes a severance benefit plan for Eligible Employees (as defined in this Plan), to be known as the ATI Inc. Executive Severance Benefit Plan

ATI Announces Third Quarter 2024 Results Ninth consecutive quarter with sales in excess of $1 billion

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Third Quarter 2024 Results Ninth consecutive quarter with sales in excess of $1 billion ◦Q3 2024 sales of $1.05 billion

ATI / ATI Inc. / STATE STREET CORP Passive Investment

SC 13G/A 1 ATIInc.htm SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* ATI INC (Name of Issuer) COMMON STOCK (Title of Class of Securities) 01741R102 (CUSIP Number) September 30, 2024 (Date of Event Which Requires Filing of This Statement) Check the appropriate box to designate the rule pursuant to which this Schedul

ATI Announces Second Quarter 2024 Results Strong performance in Aerospace & Defense propels sequential growth

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Second Quarter 2024 Results Strong performance in Aerospace & Defense propels sequential growth ◦Q2 2024 sales of $1.1 b

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2024 ☐ TRANSITION REPORT PURSUANT TO S

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 6, 2024 ATI Inc. (Exact name

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 6, 2024 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2023 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2023 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc. (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commis

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 20, 2024 (May 16, 2024) ATI Inc

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 20, 2024 (May 16, 2024) ATI Inc.

ATI Announces First Quarter 2024 Results Continued strong year-over-year revenue growth in aerospace and defense

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces First Quarter 2024 Results Continued strong year-over-year revenue growth in aerospace and defense ◦Q1 2024 sales of $1.

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April 30, 2024 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2024 ☐ TRANSITION REPORT PURSUANT TO

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

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

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: ☐ Preliminary Proxy Statement ☐ Confidential, for

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

Table of Contents 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: ☐ Preliminary Proxy Statement ☐

ATI names Vaishali Bhatia General Counsel and Chief Compliance Officer

EX-99.1 Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI names Vaishali Bhatia General Counsel and Chief Compliance Officer DALLAS, TX—March 14, 2024—ATI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 14, 2024 ATI Inc. (Exact name

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 14, 2024 ATI Inc.

Current Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 7, 2024 ATI Inc.

Form of 2024 Time-Vested Restricted Stock Unit Agreement (filed herewith)*

Exhibit 10.14 Form of 2024 Time-Vested Restricted Stock Unit Agreement This Time-Vested Restricted Stock Unit Agreement (“Agreement”) is made as of the day of January, 2024 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and #ParticipantName+C# (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated 2022 Incentive Pla

Subsidiaries of the Registrant (filed herewith).

Exhibit 21.1 SUBSIDIARIES OF THE REGISTRANT The following lists the subsidiaries of ATI Inc., excluding those subsidiaries which, considered in the aggregate as a single subsidiary, do not constitute a significant subsidiary. Name of Subsidiary State or Country of Incorporation ALC Funding Corporation Delaware Allegheny Ludlum, LLC Pennsylvania ATI Specialty Rolled Products Holdings LLC Pennsylvan

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables Form S-3 (Form Type) ATI Inc. (Exact Name of Registrant as Specified in its Charter) Table 1: Newly Registered and Carry Forward Securities Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered(1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forwa

Form of 2024 Performance-Vested Restricted Stock Unit Agreement (filed herewith)*

Exhibit 10.15 Form of 2024 Performance-Vested Restricted Stock Unit Agreement This Performance-Vested Restricted Stock Unit Agreement (this “Agreement”) is made as of the day of January, 2024 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and #ParticipantName+C# (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated

As filed with the Securities and Exchange Commission on February 23, 2024

Table of Contents As filed with the Securities and Exchange Commission on February 23, 2024 Registration No.

Current Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 23, 2024 ATI Inc.

ATI Elects Kimberly A. Fields as President and CEO Robert S. Wetherbee to become Executive Chairman

Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Elects Kimberly A. Fields as President and CEO Robert S. Wetherbee to become Executive Chairman DALLAS, T

Form of Subordinated Debt Security (included in Exhibit 4.8).

Exhibit 4.8 ATI INC. and COMPUTERSHARE TRUST COMPANY, N.A., Trustee INDENTURE Dated as of [    ] [ ], 20[ ] SUBORDINATED DEBT SECURITIES ATI INC. Certain Sections of this Indenture relating to Sections 310 through 318, inclusive, of the Trust Indenture Act of 1939, as amended Trust Indenture Act Section Indenture Section Section 310(a)(1) 609 (a)(2) 609 (a)(3) Not Applicable (a)(4) Not Applicable

Form T-1 Statement of Eligibility of Computershare Trust Company, N.A., as successor to Wells Fargo Bank, National Association, as Trustee, with respect to the Indenture dated as of September 14, 2021.

Exhibit 25.1 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM T-1 STATEMENT OF ELIGIBILITY UNDER THE TRUST INDENTURE ACT OF 1939 OF A CORPORATION DESIGNATED TO ACT AS TRUSTEE ☐ CHECK IF AN APPLICATION TO DETERMINE ELIGIBILITY OF A TRUSTEE PURSUANT TO SECTION 305(b)(2) [  ] COMPUTERSHARE TRUST COMPANY, NATIONAL ASSOCIATION (Exact name of trustee as specified in its chart

Form T-1 Statement of Eligibility of Computershare Trust Company, N.A., as Trustee, with respect to the form of subordinated debt indenture.

Exhibit 25.2 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM T-1 STATEMENT OF ELIGIBILITY UNDER THE TRUST INDENTURE ACT OF 1939 OF A CORPORATION DESIGNATED TO ACT AS TRUSTEE ☐ CHECK IF AN APPLICATION TO DETERMINE ELIGIBILITY OF A TRUSTEE PURSUANT TO SECTION 305(b)(2) [  ] COMPUTERSHARE TRUST COMPANY, NATIONAL ASSOCIATION (Exact name of trustee as specified in its chart

Preferability Letter (filed herewith).

Exhibit 18.1 February 23, 2024 Board of Directors ATI Inc. 2021 McKinney Avenue Dallas, Texas Ladies and Gentlemen: Note 1 of the Notes to the Consolidated Financial Statements of ATI Inc. and subsidiaries (the Company) included in its Annual Report on Form 10-K for the year ended December 31, 2023 describes a change in the method of accounting for recognizing actuarial gains and losses for its de

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 31, 2023 OR ☐ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission file number 1-12001 ATI Inc. (Exact n

Executive Severance Benefit Plan (filed herewith)*

Exhibit 10.16 ATI INC. EXECUTIVE SEVERANCE BENEFIT PLAN Adopted February 21, 2024 ARTICLE I NAME, PURPOSE AND EFFECTIVE DATE OF PLAN 1.1 Name of the Plan. ATI Inc. (together with its Subsidiaries, as defined in this Plan, the “Company”) hereby establishes a severance benefit plan for Eligible Employees (as defined in this Plan), to be known as the ATI Inc. Executive Severance Benefit Plan (the “Pl

ATI Inc. Executive Compensation Recovery Policy (filed herewith)

Exhibit 97.1 ATI INC. EXECUTIVE COMPENSATION RECOVERY POLICY Purpose ATI Inc. (“Company”) is establishing this Executive Compensation Recover Policy (“Policy”) to comply with Section 10D of the Securities Exchange Act of 1934 (the “Exchange Act”), Rule 10D-1 promulgated under the Exchange Act (“Rule 10D-1”), and Section 303A.14 of the New York Stock Exchange (“NYSE”) Listed Company Manual (the “Li

ATI / ATI Inc. / ALLIANCEBERNSTEIN L.P. - SEC SCHEDULE 13G Passive Investment

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1 )* ATI Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate t

ATI / ATI Inc. / ALLIANCEBERNSTEIN L.P. - SEC SCHEDULE 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1 )* ATI Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is fi

ATI / ATI Inc. / VANGUARD GROUP INC - SCHEDULE 13G/A Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G Under the Securities Exchange Act of 1934 (Amendment No.: 14)* Name of issuer: ATI Inc Title of Class of Securities: Common Stock CUSIP Number: 01741R102 Date of Event Which Requires Filing of this Statement: December 29, 2023 Check the appropriate box to designate the rule pursuant to which this Schedule is filed: ☒ Rule 13d-1

ATI / ATI Inc. / Capital International Investors - SEC SCHEDULE 13G Passive Investment

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 4 )* ATI Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 29, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 1, 2024 ATI Inc.

ATI Announces Fourth Quarter and Full Year 2023 Results Continued strong performance and year-over-year revenue growth in aerospace and defense

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Fourth Quarter and Full Year 2023 Results Continued strong performance and year-over-year revenue growth in aerospace an

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 19, 2024 ATI Inc. (Exact na

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 19, 2024 ATI Inc.

December 31 December 31 March 31 June 30 September 30 2021 2022 2023 2023 2023 ASSETS Current Assets: Cash and cash equivalents $ 687.7 $ 584.0 $ 196.2 $ 267.1 $ 432.9 Accounts receivable, net of allowances for doubtful accounts 470.0 579.2 725.6 710

ATI Inc. and Subsidiaries Consolidated Balance Sheets (unaudited) (Dollars in millions) December 31 December 31 March 31 June 30 September 30 2021 2022 2023 2023 2023 ASSETS Current Assets: Cash and cash equivalents $ 687.7 $ 584.0 $ 196.2 $ 267.1 $ 432.9 Accounts receivable, net of allowances for doubtful accounts 470.0 579.2 725.6 710.1 683.0 Short-term contract assets 53.9 64.1 52.7 51.8 56.6 I

Retirement, Transition and Release Agreement, dated as of January 8, 2024, by and between the Company and Elliot S. Davis (incorporated by reference to Exhibit 10.1 to the Registrant’s Current Report on Form 8-K dated January 10, 2024 (File No. 1-12002))*

Exhibit 10.1 RETIREMENT, TRANSITION AND RELEASE AGREEMENT This Retirement, Transition and Release Agreement (as it subsequently may be amended from time to time, this “Agreement”) is entered into as of the execution of both parties as of January 8, 2024 (“Effective Date”) by and among Elliot S. Davis (“Executive”) and ATI Inc. (together with its affiliates, the “Company”). RECITALS WHEREAS, Execut

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 10, 2024 (January 4, 2024) ATI Inc.

Regulation FD Disclosure, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 29, 2023 ATI Inc.

ATI targets 2027 revenue exceeding $5 billion on platform of organic growth Company leaders to share insights into expanding A&D business, affirm long-term strategy

Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI targets 2027 revenue exceeding $5 billion on platform of organic growth Company leaders to share insights

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 2, 2023 ATI Inc.

ATI Announces Third Quarter 2023 Results Increasing Aerospace & Defense content drives year-over-year earnings growth

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Third Quarter 2023 Results Increasing Aerospace & Defense content drives year-over-year earnings growth ◦Q3 2023 sales o

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2023 ☐ TRANSITION REPORT PURSUANT

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact nam

Current Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 18, 2023 ATI Inc.

ATI reduces U.S. defined benefit pension obligation by approximately 85% through annuitization

Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI reduces U.S. defined benefit pension obligation by approximately 85% through annuitization DALLAS, TX—Oct

Entry into a Material Definitive Agreement, Financial Statements and Exhibits, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) August 7, 2023 ATI Inc.

Underwriting Agreement, dated as of August 7, 2023, by and between ATI Inc. and Citigroup Global Markets Inc., as representative of the underwriters named therein.

Exhibit 1.1 Execution Version ATI INC. 7.250% Senior Notes due 2030 Underwriting Agreement August 7, 2023 CITIGROUP GLOBAL MARKETS INC. As Representative of the several Underwriters listed in Schedule I hereto c/o Citigroup Global Markets Inc. 388 Greenwich Street New York, NY 10013 Ladies and Gentlemen: ATI Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the several Un

Second Supplemental Indenture, dated August 11, 2023, between ATI Inc. and Computershare Trust Company, as Trustee (incorporated by reference to Exhibit 4.2 to the Registrant’s Current Report on Form 8-K dated August 11, 2023) (File No. 1-12001))

EX-4.2 Exhibit 4.2 Execution Version ATI INC. and COMPUTERSHARE TRUST COMPANY, N.A., as successor to Wells Fargo Bank, National Association, as Trustee SECOND SUPPLEMENTAL INDENTURE DATED AS OF AUGUST 11, 2023 TO THE INDENTURE DATED AS OF SEPTEMBER 14, 2021 $425,000,000 principal amount of 7.250% Senior Notes due 2030 Table of Contents Page ARTICLE I DEFINITIONS 2 SECTION 1.01. Capitalized Terms 2

ATI Inc. 7.250% Senior Notes due 2030

Table of Contents Filed Pursuant to Rule 424(b)(5) Registration No. 333-254906 P R O S P E C T U S S U P P L E M E N T (To Prospectus Dated March 31, 2021) ATI Inc. $425,000,000 7.250% Senior Notes due 2030 We are offering $425,000,000 aggregate principal amount of our 7.250% Senior Notes due 2030 (the “notes”). The notes will mature on August 15, 2030. Interest will accrue from August 11, 2023, a

Calculation of Filing Fee Tables (Form Type) ATI Inc. (Exact Name of Registrant as Specified in its Charter) Table 1: Newly Registered and Carry Forward Securities Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Regist

Exhibit 107 Calculation of Filing Fee Tables 424B5 (Form Type) ATI Inc. (Exact Name of Registrant as Specified in its Charter) Table 1: Newly Registered and Carry Forward Securities Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forward For

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) August 7, 2023 ATI Inc.

Pricing Term Sheet ATI Inc. $425,000,000 7.250% Senior Notes due 2030

Filed Pursuant to Rule 433 Registration Statement No. 333-254906 August 7, 2023 Pricing Term Sheet ATI Inc. $425,000,000 7.250% Senior Notes due 2030 This term sheet to the preliminary prospectus supplement dated August 7, 2023 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

ATI Announces Pricing of Senior Notes Offering

EX-99.1 Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] ATI Announces Pricing of Senior Notes Offering DALLAS, TX — August 7, 2023 — ATI Inc. (NYSE: ATI) announced today that it

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) August 7, 2023 ATI Inc.

SUBJECT TO COMPLETION, DATED AUGUST 7, 2023

Table of Contents Filed Pursuant to Rule 424(b)(3) Registration No. 333-254906 The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and we are not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permit

ATI Announces Proposed Senior Notes Offering

EX-99.1 Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.394.2908 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] ATI Announces Proposed Senior Notes Offering DALLAS, TX — August 7, 2023 — ATI Inc. (NYSE: ATI) announced today its intent

ATI Announces Second Quarter 2023 Results Strong performance in Aerospace & Defense propels sequential and year over year growth

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters David Weston Natalie Gillespie 2021 McKinney Avenue 412-394-2908 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Second Quarter 2023 Results Strong performance in Aerospace & Defense propels sequential and year over year growth ◦Q2 2

Amendment No. 2, dated as of September 9, 2022, to First Amended and Restated Revolving Credit, Term Loan, Delayed Draw Term Loan and Security Agreement, dated as of September 30, 2019, by and among the borrowers party thereto, the Company and other guarantors party thereto, the lenders party thereto, and PNC Bank, National Association, as Lender and Agent (filed herewith).

Exhibit 10.1 AMENDMENT NO. 2 TO FIRST AMENDED AND RESTATED REVOLVING CREDIT, TERM LOAN AND SECURITY AGREEMENT THIS AMENDMENT NO. 2 TO FIRST AMENDED AND RESTATED REVOLVING CREDIT, TERM LOAN AND SECURITY AGREEMENT (this "Amendment") is dated as of September 9, 2022 (the "Effective Date") (subject to Paragraph 5 below) and is made by and among OREGON METALLURGICAL, LLC, an Oregon limited liability co

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2023 ☐ TRANSITION REPORT PURSUANT TO S

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 2, 2023 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2022 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2022 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 6, 2023 ATI Inc. (Exact name o

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 6, 2023 ATI Inc.

Kimberly Fields Named President and Chief Operating Officer Driving strategic growth through tightly aligned operations and disciplined execution

EX-99.1 Exhibit 99.1 NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Tom Wright Natalie Gillespie 2021 McKinney Avenue, Suite 1100 412.258.4781 412.389.3124 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com Kimberly Fields Named President and Chief Operating Officer Driving strategic growth through tightly alig

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc. (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commis

Form SD UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report ATI Inc.

Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 15, 2023 (May 11, 2023) ATI Inc.

ATI Announces First Quarter 2023 Results Aerospace and Defense sales propel strong year over year growth

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Tom Wright Natalie Gillespie 2021 McKinney Avenue 412-258-4781 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces First Quarter 2023 Results Aerospace and Defense sales propel strong year over year growth ◦Q1 2023 sales of $1.04 billion u

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 4, 2023 (April 28, 2023) ATI In

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 4, 2023 (April 28, 2023) ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2023 ☐ TRANSITION REPORT PURSUANT TO

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

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

DEFA14A 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: ☐ Preliminary Proxy Statement ☐ Confidential, fo

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

Table of Contents 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: ☐ Preliminary Proxy Statement ☐ Confid

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

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: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 1, 2023 ATI Inc.

Global Financial Expert Ruby Sharma Joins ATI Board

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Tom Wright Natalie Gillespie 2021 McKinney Avenue 412-258-4781 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com Global Financial Expert Ruby Sharma Joins ATI Board DALLAS, TX—March 2, 2023—ATI Inc. (NYSE: ATI) today announced that Ruby Sharma has bee

Subsidiaries of the Registrant (filed herewith).

Exhibit 21.1 SUBSIDIARIES OF THE REGISTRANT The following lists the subsidiaries of ATI Inc., excluding those subsidiaries which, considered in the aggregate as a single subsidiary, do not constitute a significant subsidiary. Name of Subsidiary State or Country of Incorporation ALC Funding Corporation Delaware Allegheny Ludlum, LLC Pennsylvania ATI Flat Rolled Products Holdings LLC Pennsylvania AT

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 31, 2022 OR ☐ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission file number 1-12001 ATI Inc. (Exact n

Form of 2023 Time-Vested Restricted Stock Unit Agreement (incorporated by reference to Exhibit 10,12 to the Registrant’s Annual Report on Form 10-K for the year ended December 31, 2022 (File No. 1-12001))*

Exhibit 10.12 Form of 2023 Time-Vested Restricted Stock Unit Agreement This Time-Vested Restricted Stock Unit Agreement (“Agreement”) is made as of the day of January, 2023 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and #ParticipantName+C# (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated 2022 Incentive Pla

Form of 2023 Performance-Vested Restricted Stock Unit Agreement (incorporated by reference to Exhibit 10,13 to the Registrant’s Annual Report on Form 10-K for the year ended December 31, 2022 (File No. 1-12001))*

Exhibit 10.13 Form of 2023 Performance-Vested Restricted Stock Unit Agreement This Performance-Vested Restricted Stock Unit Agreement (this “Agreement”) is made as of the day of January, 2023 (the “Grant Date”) by and between ATI Inc., a Delaware company (the “Company”), and #ParticipantName+C# (the “Participant”). WHEREAS, the Company sponsors and maintains the Allegheny Technologies Incorporated

ATI / Allegheny Technologies Incorporated / ALLIANCEBERNSTEIN L.P. - SEC SCHEDULE 13G Passive Investment

SC 13G 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* ATI Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2022 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the r

ATI / Allegheny Technologies Incorporated / Capital International Investors - SEC SCHEDULE 13G Passive Investment

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 3 )* ATI Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 30, 2022 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate

ATI / Allegheny Technologies Incorporated / ALLIANCEBERNSTEIN L.P. - SEC SCHEDULE 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* ATI Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2022 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is file

ATI / Allegheny Technologies Incorporated / VANGUARD GROUP INC - SCHEDULE 13G/A Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G Under the Securities Exchange Act of 1934 (Amendment No.: 13)* Name of issuer: ATI Inc. Title of Class of Securities: Common Stock CUSIP Number: 01741R102 Date of Event Which Requires Filing of this Statement: December 30, 2022 Check the appropriate box to designate the rule pursuant to which this Schedule is filed: ☒ Rule 13d-

ATI Announces Fourth Quarter 2022 Results Continued strong performance and year-over-year revenue growth in aerospace and defense

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Tom Wright Natalie Gillespie 2021 McKinney Avenue 412-258-4781 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Fourth Quarter 2022 Results Continued strong performance and year-over-year revenue growth in aerospace and defense ◦Q4 2022

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 2, 2023 ATI Inc. (Exact na

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 2, 2023 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2022 ☐ TRANSITION REPORT PURSUANT

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact nam

Amendment No. 2, dated as of September 9, 2022, to First Amended and Restated Revolving Credit, Term Loan, Delayed Draw Term Loan and Security Agreement, dated as of September 30, 2019, by and among the borrowers party thereto, the Company and other guarantors party thereto, the lenders party thereto, and PNC Bank, National Association, as Lender and Agent (filed herewith).

Exhibit 10.1 AMENDMENT NO. 2 TO First AMENDED AND RESTATED revolving credit, term loan and security agreement THIS AMENDMENT NO. 2 to FIRST AMENDED AND RESTATED revolving credit, term loan and security agreement (this "Amendment") is dated as of September 9, 2022 (the "Effective Date") (subject to Paragraph 5 below) and is made by and among Oregon Metallurgical, LLC, an Oregon limited liability co

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 2, 2022 ATI INC.

ATI Announces Third Quarter 2022 Results Continued strong sequential and year-over-year revenue growth in aerospace and defense markets

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Tom Wright Natalie Gillespie 2021 McKinney Avenue 412-258-4781 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Third Quarter 2022 Results Continued strong sequential and year-over-year revenue growth in aerospace and defense markets ?S

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K/A (Amendment No.

Retirement, Transition and Release Agreement, dated as of October 12, 2022, by and between the Company and Kevin B. Kramer (incorporated by reference to Exhibit 10.1 to the Registrant’s Current Report on Form 8-K dated October 14, 2022 (File No. 1-12002)).

Exhibit 10.1 RETIREMENT, TRANSITION AND RELEASE AGREEMENT This Retirement, Transition and Release Agreement (as it subsequently may be amended from time to time, this ?Agreement?) is entered into as of October 12, 2022 (?Effective Date?) by and among Kevin B. Kramer (?Executive?) and ATI Inc. (together with its affiliates, the ?Company?). RECITALS WHEREAS, Executive and the Company have agreed tha

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): September 22, 2022 ATI Inc.

Entry into a Material Definitive Agreement, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): September 9, 2022 ATI Inc.

ATI Announces Second Quarter 2022 Results Strong jet engine sales growth and operating discipline drive improved financial performance

NEWS RELEASE ATI Inc. Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 2021 McKinney Avenue 412-395-2720 412-394-2850 Dallas, TX 75201 U.S.A. [email protected] [email protected] www.ATImaterials.com ATI Announces Second Quarter 2022 Results Strong jet engine sales growth and operating discipline drive improved financial performa

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2022 ☐ TRANSITION REPORT PURSUANT TO S

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ATI Inc. (Exact name of

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 4, 2022 ATI INC.

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): July 8, 2022 ATI Inc.

Certificate of Amendment of Certificate of Incorporation (incorporated by reference to Exhibit 3.1 to the Registrant’s Current Report on Form 8-K dated June 22, 2022 (File No. 1-12001).

Exhibit 3.1 STATE OF DELAWARE CERTIFICATE OF AMENDMENT OF CERTIFICATE OF INCORPORATION Pursuant to Section 242 of the General Corporation Law of the State of Delaware, Allegheny Technologies Incorporated, a corporation duly organized and existing under the General Corporation Law of the State of Delaware (the ?Corporation?) does hereby certify: FIRST: Article ONE of the Restated Certificate of Inc

Fourth Amended and Restated Bylaws

EX-3.2 3 d314796dex32.htm EX-3.2 Exhibit 3.2 ATI INC. FOURTH AMENDED AND RESTATED BYLAWS Dated as of June 22, 2022 TABLE OF CONTENTS Page ARTICLE I OFFICES 1 Section 1. Registered Office 1 Section 2. Offices 1 ARTICLE II MEETINGS OF STOCKHOLDERS 1 Section 1. Place of Meetings 1 Section 2. Annual Meeting 1 Section 3. Special Meetings 4 Section 4. Notice of Meetings; Waiver 4 Section 5. Quorum; Adjo

Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 22, 2022 ATI Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ? ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2021 ? TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ? ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2021 ? TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQ

Filing Fee Table.

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in its Charter) Table 1: Newly Registered and Carry Forward Securities Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered(1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forward Form Type Carry Forward File Number Carry Forward Initial effective date Filing Fee Previously Paid In Connection with Unsold Securities to be Carried Forward Newly Registered Securities Fees to Be Paid Equity Common Stock, par value $0.

SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 POST-EFFECTIVE AMENDMENT NO. 1 FORM S-8 REGISTRATION STATEMENT THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25

Registration No. 333-238169 SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 POST-EFFECTIVE AMENDMENT NO. 1 to FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25-1792394 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 1000

SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-8 REGISTRATION STATEMENT THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25-1792394 (State or other jurisd

Registration No. 333- SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25-1792394 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 1000 Six PPG Place Pittsburgh, Pennsylvania

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdictio

SD 1 d312845dsd.htm FORM SD UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commission File Number) (IRS Employer Identification Number) 1000 Six PPG Place, Pittsburgh, Pennsylv

Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 13, 2022 (May 12, 2022) Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Announces First Quarter 2022 Results Aerospace-driven growth continues, with ongoing focus on ramp readiness to support customers

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 4, 2022 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2022 ☐ TRANSITION REPORT PURSUANT TO

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOGIES

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

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: ? Preliminary Proxy Statement ? Confidential, for Use of

March 30, 2022

CORRESP 1 filename1.htm 1000 Six PPG Place Pittsburgh, PA 15222-5479 WWW.ATIMETALS.COM March 30, 2022 United States Securities and Exchange Commission Division of Corporation Finance 100 F. Street N.E. Washington, D.C. 20549-7010 Attn: Claire Erlanger RE: Allegheny Technologies Incorporated File No. 1-12001 Dear Ms. Erlanger: This letter sets forth our response to the letter (the “Comment Letter”)

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

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: ? Preliminary Proxy Statement ? Confidential, for Use of

Allegheny Technologies Incorporated 2022 Incentive Plan (incorporated by reference to Appendix A to the Registrant’s Definitive Proxy Statement filed on March 25, 2022 (File No 1-12001)).

DEF 14A 1 d448952ddef14a.htm DEF 14A Table of Contents 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: ☐

Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] natalie.gillespie@a

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 9, 2022 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Regulation FD Disclosure, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 3, 2022 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Form of Performance-Vested Restricted Stock Unit Agreement (incorporated by reference to Exhibit 10-15 to the Registrant’s Annual Report on Form 10-K for the year ended December 31, 2021 (File No. 1-12001)*

Exhibit 10.15 FORM OF BREAKOUT PERFORMANCE AWARD AGREEMENT PURSUANT TO THE ALLEGHENY TECHNOLOGIES INCORPORATED 2020 INCENTIVE PLAN This Breakout Performance Award Agreement (this ?Agreement?) is made as of the 4th day of January, 2022 (the ?Grant Date?) by and between ALLEGHENY TECHNOLOGIES INCORPORATED, a Delaware company (the ?Company?), and [Participant Name] (the ?Participant?). WHEREAS, the C

LIFO Preferability Lette

Exhibit 18.1 February 25, 2022 Board of Directors Allegheny Technologies Incorporated 1000 Six PPG Place Pittsburgh, PA 15222 Ladies and Gentlemen: Note 1 of the Notes to the consolidated financial statements of Allegheny Technologies Incorporated included in its Annual Report on Form 10-K for the year ended December 31, 2021 describes a change in the method of accounting for valuing inventories t

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ? Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 31, 2021 OR ? Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission file number 1-12001 ALLEGHENY TECHNOL

Subsidiaries of the Registrant (filed herewith).

Exhibit 21.1 SUBSIDIARIES OF THE REGISTRANT The following lists the subsidiaries of Allegheny Technologies Incorporated, excluding those subsidiaries which, considered in the aggregate as a single subsidiary, do not constitute a significant subsidiary. Name of Subsidiary State or Country of Incorporation ALC Funding Corporation Delaware Allegheny Ludlum, LLC Pennsylvania ATI Flat Rolled Products H

ATI / Allegheny Technologies Incorporated / Capital International Investors - SEC SCHEDULE 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2 )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2021 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which

ATI / Allegheny Technologies Incorporated / VANGUARD GROUP INC - SCHEDULE 13G/A Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G Under the Securities Exchange Act of 1934 (Amendment No.: 12)* Name of issuer: Allegheny Technologies Inc. Title of Class of Securities: Common Stock CUSIP Number: 01741R102 Date of Event Which Requires Filing of this Statement: December 31, 2021 Check the appropriate box to designate the rule pursuant to which this Schedule is

ATI / Allegheny Technologies Incorporated / DIMENSIONAL FUND ADVISORS LP - SEC SCHEDULE 13G Passive Investment

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2 )* Allegheny Technologies Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2021 (Date of Event Which Requires Filing of this Statement) Check the appropriate

ATI Announces Fourth Quarter 2021 Results Strong growth and profit margin expansion as aerospace recovery accelerates

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

ATI Board of Directors Authorizes $150 Million Share Repurchase

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Regulation FD Disclosure, Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 2, 2022 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2021 ☐ TRANSITION REPORT PURSUANT

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2021 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOG

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 28, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Announces Third Quarter 2021 Results Return to profitability fueled by aerospace market recovery and business transformation

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 21, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Kimberly Fields Named Chief Operating Officer, Don Newman EVP Driving revenue growth through tightly aligned operations and financial discipline

Exhibit 99.1 NEWS RELEASE Allegheny Technologies Incorporated Corporate Headquarters 1000 Six PPG Place Pittsburgh, PA 15222-5479 U.S.A. www.ATImetals.com Investor Contact: Scott A. Minder 412-395-2720 [email protected] Media Contact: Natalie Gillespie 412-394-2850 [email protected] Kimberly Fields Named Chief Operating Officer, Don Newman EVP Driving revenue growth through

(incorporated by reference to Exhibit 4.1 to the Registrant’s Current Report on Form 8-K filed on September 14, 2021 (File No. 1-12001)).

Exhibit 4.1 ALLEGHENY TECHNOLOGIES INCORPORATED and WELLS FARGO BANK, NATIONAL ASSOCIATION, Trustee INDENTURE Dated as of September 14, 2021 SENIOR DEBT SECURITIES ALLEGHENY TECHNOLOGIES INCORPORATED Certain Sections of this Indenture relating to Sections 310 through 318, inclusive, of the Trust Indenture Act of 1939, as amended Trust Indenture Act Section Indenture Section Section 310(a)(1) 609 (

Entry into a Material Definitive Agreement, Financial Statements and Exhibits, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) September 9, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Underwriting Agreement, dated as of September 9, 2021, by and between Allegheny Technologies Incorporated and BofA Securities, Inc., as representative of the underwriters named therein.

Exhibit 1.1 EXECUTION VERSION BOFA SECURITIES, INC. ALLEGHENY TECHNOLOGIES INCORPORATED 4.875% Senior Notes due 2029 5.125% Senior Notes due 2031 Underwriting Agreement September 9, 2021 BOFA SECURITIES, INC. As Representative of the several Underwriters listed in Schedule I hereto c/o BofA Securities, Inc. One Bryant Park New York, New York 10036 Ladies and Gentlemen: Allegheny Technologies Incor

Form of 5.125% Senior Note due 2031 (incorporated by reference to Exhibit 4.2 to the Registrant’s Current Report on Form 8-K dated September 14, 2021 (File No. 1-12001))

Exhibit 4.2 EXECUTION COPY ALLEGHENY TECHNOLOGIES INCORPORATED and WELLS FARGO BANK, NATIONAL ASSOCIATION, as Trustee FIRST SUPPLEMENTAL INDENTURE DATED AS OF SEPTEMBER 14, 2021 TO THE INDENTURE DATED AS OF SEPTEMBER 14, 2021 $325,000,000 principal amount of 4.875% Senior Notes due 2029 $350,000,000 principal amount of 5.125% Senior Notes due 2031 Table of Contents Page ARTICLE I DEFINITIONS 2 SEC

Allegheny Technologies Announces Pricing of Senior Notes Offering

Exhibit 99.1 NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] [email protected] www.ATImetals.com Allegheny Technologies Announces Pricing of Senior Notes Offering PITTSBURGH, Pennsylvania ?

CALCULATION OF REGISTRATION FEE Title of each class of securities offered Amount to be registered Maximum offering price per unit Maximum aggregate offering price Amount of registration fee(1) 4.875% Notes due 2029 $325,000,000 100% $325,000,000 $35,

424B5 1 d196748d424b5.htm 424B5 Table of Contents CALCULATION OF REGISTRATION FEE Title of each class of securities offered Amount to be registered Maximum offering price per unit Maximum aggregate offering price Amount of registration fee(1) 4.875% Notes due 2029 $325,000,000 100% $325,000,000 $35,457.50 5.125% Notes due 2031 $350,000,000 100% $350,000,000 $38,185.00 Total $675,000,000 $675,000,0

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) September 9, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Pricing Term Sheet Allegheny Technologies Incorporated $325,000,000 4.875% Senior Notes due 2029 $350,000,000 5.125 % Senior Notes due 2031

Filed Pursuant to Rule 433 Registration Statement No. 333-254906 September 9, 2021 Pricing Term Sheet Allegheny Technologies Incorporated $325,000,000 4.875% Senior Notes due 2029 $350,000,000 5.125 % Senior Notes due 2031 This term sheet to the preliminary prospectus supplement dated September 8, 2021 should be read together with the preliminary prospectus supplement before making a decision in c

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) September 8, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

SUBJECT TO COMPLETION, DATED SEPTEMBER 8, 2021

Table of Contents Filed Pursuant to Rule 424(b)(3) Registration No. 333-254906 The information in this preliminary prospectus supplement and the accompanying prospectus is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and they are not soliciting an offer to buy these securities in any state where th

Allegheny Technologies Announces Proposed Senior Notes Offering

Exhibit 99.1 Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] [email protected] www.ATImetals.com Allegheny Technologies Announces Proposed Senior Notes Offering PITTSBURGH, Pennsylvania ? September 8, 20

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 16, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Completes Sale of Flowform Products to Consolidated Boring, Inc.

Exhibit 99.1 NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] [email protected] www.ATImetals.com ATI Completes Sale of Flowform Products to Consolidated Boring, Inc. PITTSBURGH, PA?August 16

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2021 ☐ TRANSITION REPORT PURSUANT TO S

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2021 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOGIES I

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 3, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Addendum to Performance-Vested Restricted Stock Unit Agreement (filed herewith).

Exhibit 10.1 ADDENDUM TO PERFORMANCE-VESTED RESTRICTED STOCK UNIT AGREEMENT PURSUANT TO THE ALLEGHENY TECHNOLOGIES INCORPORATED 2020 INCENTIVE PLAN This Addendum (this ?Addendum?) to that certain Performance-Vested Restricted Stock Unit Agreement (the ?Agreement?) dated as of the 4th day of January, 2021 (the ?Grant Date?) by and between ALLEGHENY TECHNOLOGIES INCORPORATED, a Delaware company (the

ATI Announces Second Quarter 2021 Results Aerospace recovery continues to gain momentum Labor strike resolved, business transformation on track

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

ATI and United Steelworkers Reach Tentative Agreement

Exhibit 99.1 NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] [email protected] www.ATImetals.com ATI and United Steelworkers Reach Tentative Agreement PITTSBURGH, PA?July 6, 2021?Allegheny T

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): July 6, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

11-K 1 fy202011-kati401ksavingspl.htm 11-K UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2020 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

11-K 1 fy202011katiretirementplan.htm 11-K UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2020 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdictio

SD 1 d175553dsd.htm SD UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commission File Number) (IRS Employer Identification Number) 1000 Six PPG Place, Pittsburgh, Pennsylvania

Regulation FD Disclosure, Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits, Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 21, 2021 (May 20, 2021) Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

CEO Robert S. Wetherbee Becomes ATI Board Chair J. Brett Harvey named Lead Independent Director

Exhibit 99.1 Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A. Minder Natalie Gillespie 1000 Six PPG Place 412-395-2720 412-394-2850 Pittsburgh, PA 15222-5479 U.S.A. [email protected] [email protected] www.ATImetals.com CEO Robert S. Wetherbee Becomes ATI Board Chair J. Brett Harvey named Lead Independent Director PITTSBURGH

SCHEDULE 13G

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1 )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) April 30, 2021 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which th

Quarterly Report - 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended March 31, 2021 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOGIES

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April 29, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Announces First Quarter 2021 Results Exceeds expectations with benefit from strong raw material price tailwinds Ongoing modest recovery in jet engine production

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

- DEF 14A

DEF 14A 1 d12507ddef14a.htm DEF 14A Table of Contents 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: ☐

- DEFA14A

DEFA14A 1 d12507ddefa14a.htm DEFA14A 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: ☐ Preliminary Proxy

As filed with the Securities and Exchange Commission on March 31, 2021

Table of Contents As filed with the Securities and Exchange Commission on March 31, 2021 Registration No.

Form of Subordinated Debt Security (included in Exhibit 4.12).

Exhibit 4.12 ALLEGHENY TECHNOLOGIES INCORPORATED and [ ], Trustee INDENTURE Dated as of [ ] [ ], 20[ ] SUBORDINATED DEBT SECURITIES ALLEGHENY TECHNOLOGIES INCORPORATED Certain Sections of this Indenture relating to Sections 310 through 318, inclusive, of the Trust Indenture Act of 1939, as amended Trust Indenture Act Section Indenture Section Section 310(a)(1) 609 (a)(2) 609 (a)(3) Not Applicable

Form of Senior Debt Security (included in Exhibit 4.10).

Exhibit 4.10 ALLEGHENY TECHNOLOGIES INCORPORATED and [ ], Trustee INDENTURE Dated as of [ ] [ ], 20[ ] SENIOR DEBT SECURITIES ALLEGHENY TECHNOLOGIES INCORPORATED Certain Sections of this Indenture relating to Sections 310 through 318, inclusive, of the Trust Indenture Act of 1939, as amended Trust Indenture Act Section Indenture Section Section 310(a)(1) 609 (a)(2) 609 (a)(3) Not Applicable (a)(4)

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 2, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Consulting Agreement dated February 28, 2021

Exhibit 10.1 CONSULTING AGREEMENT This Consulting Agreement (as it subsequently may be amended from time to time, this ?Agreement?) is entered into as of February 28, 2021 (?Effective Date?) by and among John D. Sims (?Consultant?) and Allegheny Technologies Incorporated (together with its affiliates, the ?Company?). RECITALS WHEREAS, Consultant has retired from his position with the Company as Se

Form of Performance-Vested Restricted Stock Unit Agreement (Filed herewith).*

Exhibit 10.17 PERFORMANCE-VESTED RESTRICTED STOCK UNIT AGREEMENT PURSUANT TO THE ALLEGHENY TECHNOLOGIES INCORPORATED 2020 INCENTIVE PLAN This Performance-Vested Restricted Stock Unit Agreement (this ?Agreement?) is made as of the 4th day of January, 2021 (the ?Grant Date?) by and between ALLEGHENY TECHNOLOGIES INCORPORATED, a Delaware company (the ?Company?), and #ParticipantName# (the ?Participan

Form of Time-Vested Restricted Stock Unit Agreement (Filed herewith).*

Exhibit 10.16 TIME-VESTED RESTRICTED STOCK UNIT AGREEMENT PURSUANT TO THE ALLEGHENY TECHNOLOGIES INCORPORATED 2020 INCENTIVE PLAN This Time-Vested Restricted Stock Unit Agreement (?Agreement?) is made as of the 4th day of January, 2021 (the ?Grant Date?) by and between ALLEGHENY TECHNOLOGIES INCORPORATED, a Delaware company (the ?Company?), and #ParticipantName# (the ?Participant?). WHEREAS, the C

Annual Report - 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ? Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 31, 2020 OR ? Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission file number 1-12001 ALLEGHENY TECHNOL

Subsidiaries of the Registrant (filed herewith).

Exhibit 21.1 SUBSIDIARIES OF THE REGISTRANT The following lists the subsidiaries of Allegheny Technologies Incorporated, excluding those subsidiaries which, considered in the aggregate as a single subsidiary, do not constitute a significant subsidiary. Name of Subsidiary State or Country of Incorporation ALC Funding Corporation Delaware Allegheny Ludlum, LLC Pennsylvania ATI Flat Rolled Products H

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G (Amendment No. 1) Under the Securities Exchange Act of 1934 Allegheny Technologies Incorporated (Name of Issuer) Common Stock, $0.10 par value (Title of Class of Securities) (CUSI

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G (Amendment No. 1) Under the Securities Exchange Act of 1934 Allegheny Technologies Incorporated (Name of Issuer) Common Stock, $0.10 par value (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the following box to designate the rule pursuant t

JOINT FILING AGREEMENT

Exhibit 2 JOINT FILING AGREEMENT In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, each of the undersigned Reporting Persons hereby agrees to the joint filing, along with all other such Reporting Persons, on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock, $0.

SCHEDULE 13G

SC 13G 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriate bo

SCHEDULE 13G

SC 13G 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriate bo

SCHEDULE 13G

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1 )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriat

POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940

Exhibit 1 POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940 I, David E.

SCHEDULE 13G

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2 )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriat

SCHEDULE 13G

SC 13G/A 1 SEC13GFiling.htm SEC SCHEDULE 13G UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1 )* Allegheny Technologies Inc (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) December 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriate

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G Under the Securities Exchange Act of 1934 (Amendment No.: 11)*

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G Under the Securities Exchange Act of 1934 (Amendment No.: 11)* Name of issuer: Allegheny Technologies Inc. Title of Class of Securities: Common Stock CUSIP Number: 01741R102 Date of Event Which Requires Filing of this Statement: December 31, 2020 Check the appropriate box to designate the rule pursuant to which this Schedule is

ATI Announces Fourth Quarter 2020 Results Exceeds expectations through strong cost control; Signs of commercial aero stabilization Actions to exit standard stainless sheet products and enhance high-return capabilities on-track

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 28, 2021 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Exits Standard Stainless Sheet Products, Redeploys Capital to High-Return Opportunities

Exhibit 99.1 ATI Exits Standard Stainless Sheet Products, Redeploys Capital to High-Return Opportunities Actions increase aerospace and defense focus and improve profitability Exiting $445 million of very low-margin products; ceasing production at five facilities and consolidating finishing operations Streamlined footprint and investment to enhance capabilities expected to deliver returns of ~3x c

Regulation FD Disclosure, Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits, Material Impairments, Costs Associated with Exit or Disposal Activities

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): December 4, 2020 (December 2, 2020) Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 001-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 24, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Quarterly Report - 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended September 30, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOG

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 29, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI Announces Third Quarter 2020 Results Delivering cost savings ahead of schedule

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

- SD

SD 1 d19545dsd.htm SD UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM SD Specialized Disclosure Report Allegheny Technologies Incorporated (Exact Name of Registrant as Specified in Charter) Delaware 1-12001 25-1792394 (State or Other Jurisdiction of Incorporation) (Commission File Number) (IRS Employer Identification Number) 1000 Six PPG Place, Pittsburgh, Pennsylvania 1

POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940

Exhibit 1 POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940 I, David E.

JOINT FILING AGREEMENT

Exhibit 2 JOINT FILING AGREEMENT In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, each of the undersigned Reporting Persons hereby agrees to the joint filing, along with all other such Reporting Persons, on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock, $0.

ATI / Allegheny Technologies, Inc. / D. E. SHAW & CO, L.P. - SC 13G Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 Allegheny Technologies Incorporated (Name of Issuer) Common Stock, $0.10 par value (Title of Class of Securities) 01741R102 (CUSIP Number) September 8, 2020 (Date of Event Which Requires Filing of this Statement) Check the following box to designate the rule pursuant to which the Schedu

ATI / Allegheny Technologies, Inc. / Capital International Investors - SEC SCHEDULE 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2 )* Allegheny Technologies Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 01741R102 (CUSIP Number) August 31, 2020 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which t

ATI Announces Second Quarter 2020 Results

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Quarterly Report - 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Quarterly Period Ended June 30, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOGIES I

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 4, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Indenture, dated June 22, 2020, by and between the Company The Bank of New York Mellon, as trustee (incorporated by reference to Exhibit 4.1 to the Registrant’s Current Report on Form 8-K dated June 22, 2020 (File No. 1-12001))

EX-4.1 Exhibit 4.1 EXECUTION VERSION ALLEGHENY TECHNOLOGIES INCORPORATED AND THE BANK OF NEW YORK MELLON, as Trustee INDENTURE Dated as of June 22, 2020 3.50% Convertible Senior Notes due 2025 TABLE OF CONTENTS Page ARTICLE 1 Definitions Section 1.01. Definitions 1 Section 1.02. References to Interest 12 ARTICLE 2 Issue, Description, Execution, Registration and Exchange of Notes Section 2.01. Desi

Entry into a Material Definitive Agreement, Unregistered Sales of Equity Securities, Financial Statements and Exhibits, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) June 22, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Form of Capped Call Confirmation (incorporated by reference to Exhibit 10.1 to the Registrant’s Current Report on Form 8-K dated June 22, 2020 (File No. 1-12001))

EX-10.1 Exhibit 10.1 [Dealer] [Address] [ ], 2020 To: Allegheny Technologies Incorporated 1000 Six PPG Place Pittsburgh, PA 15222-5479 Attention: Telephone No.: Facsimile No.: [Title of contact] [ ] [ ] Re: [Base][Additional] Call Option Transaction The purpose of this letter agreement (this “Confirmation”) is to confirm the terms and conditions of the call option transaction entered into between

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) June 17, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Allegheny Technologies Announces Pricing of $285.0 Million Convertible Notes Offering

EX-99.1 Exhibit 99.1 Allegheny Technologies Announces Pricing of $285.0 Million Convertible Notes Offering PITTSBURGH, Pennsylvania – June 17, 2020 — Allegheny Technologies Incorporated (NYSE: ATI) announced today the pricing of $285.0 million aggregate principal amount of 3.5% Convertible Senior Notes due 2025 (the “Notes”) in a private placement to qualified institutional buyers pursuant to Rule

Allegheny Technologies Announces Proposed Convertible Notes Offering Intends to Repurchase a Portion of its 2022 Notes

EX-99.1 Exhibit 99.1 Allegheny Technologies Announces Proposed Convertible Notes Offering Intends to Repurchase a Portion of its 2022 Notes PITTSBURGH-(BUSINESS WIRE)-Allegheny Technologies Incorporated (NYSE: ATI) announced today its intention to offer, subject to market and other conditions, a series of convertible senior notes (the “Notes”) in a private placement to qualified institutional buye

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported) June 17, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Regulation FD Disclosure

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): June 16, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI / Allegheny Technologies, Inc. / D. E. SHAW & CO, L.P. - SC 13G Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 Allegheny Technologies Incorporated (Name of Issuer) Common Stock, $0.10 par value (Title of Class of Securities) 01741R102 (CUSIP Number) June 5, 2020 (Date of Event Which Requires Filing of this Statement) Check the following box to designate the rule pursuant to which the Schedule is

POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940

Exhibit 1 POWER OF ATTORNEY FOR CERTAIN REGULATORY FILINGS INCLUDING CERTAIN FILINGS UNDER THE SECURITIES EXCHANGE ACT OF 1934 AND THE INVESTMENT ADVISERS ACT OF 1940 I, David E.

JOINT FILING AGREEMENT

Exhibit 2 JOINT FILING AGREEMENT In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, each of the undersigned Reporting Persons hereby agrees to the joint filing, along with all other such Reporting Persons, on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock, $0.

- 11-K

11-K 1 fy201911-kati401ksavingsplan.htm 11-K UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2019 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF TH

- 11-K

11-K 1 fy201911katiretirementplan.htm 11-K UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 ý ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED] FOR THE FISCAL YEAR ENDED DECEMBER 31, 2019 ¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE

Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 22, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Dec 2014

PART I Item 1. Business The Company Allegheny Technologies Incorporated is a Delaware corporation with its principal executive offices located at 1000 Six PPG Place, Pittsburgh, Pennsylvania 15222-5479, telephone number (412) 394-2800, Internet website address www.atimetals.com. Our Internet website and the content contained therein or connected thereto are not intended to be incorporated into thi

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 12, 2020 (May 8, 2020) Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

- S-8 POS

S-8 POS Registration No. 333-217942 SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 POST-EFFECTIVE AMENDMENT NO. 1 to FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25-1792394 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification N

- FORM S-8

Form S-8 Registration No. 333- SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 ALLEGHENY TECHNOLOGIES INCORPORATED (Exact name of registrant as specified in its charter) Delaware 25-1792394 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 1000 Six PPG Place Pittsburgh, Penn

Quarterly Report - 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934For the Quarterly Period Ended March 31, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period From to Commission File Number 1-12001 ALLEGHENY TECHNOLOGIES I

ATI Announces First Quarter 2020 Results

NEWS RELEASE Allegheny Technologies Incorporated Investor Contact: Media Contact: Corporate Headquarters Scott A.

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 5, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April 21, 2020 Allegheny Technologies Incorporated (Exact name of registrant as specified in its charter) Delaware 1-12001 25-1792394 (State or other jurisdiction of incorporation) (Commission File Number) (IRS Employer Identification No.

ATI / Allegheny Technologies, Inc. DEFA14A - - DEFA14A

DEFA14A 1 d915764ddefa14a.htm DEFA14A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as

ATI / Allegheny Technologies, Inc. DEFA14A - - DEFA14A

DEFA14A 1 d915764ddefa14a.htm DEFA14A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as

ATI / Allegheny Technologies, Inc. DEFA14A - - DEFA14A

DEFA14A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))