| As Of | Filing | | Doc. | | Page | | Title | Docs. |
|---|
| | |  |
| 2/23/24 | | S-3ASR | | | | 1 | | About This Prospectus | 3 |
| 8/8/23 | | 424B5 | | | | 1 | | About This Prospectus Supplement | 2 |
| 3/28/24 | | DEF 14A | | | | 1 | | Advisory Vote to Approve the Compensation of the Company's Named Executive Officers | 1 |
| 2/23/24 | | 10-K | | | | 1 | | And | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Annual Meeting Information | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Ars Ended December 31, 202 | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | ATI Corporate Governance at a Glance | 1 |
| | | | | | 1 | | ATI's Executive Management | 1 |
| | | | | | 1 | | Audit and Risk Committee Report | 1 |
| | | | | | 1 | | Base Salary | 1 |
| | | | | | 1 | | Benchmarking Peer Group | 1 |
| | | | | | 1 | | Board Committees | 1 |
| | | | | | 1 | | Board Independence | 1 |
| | | | | | 1 | | Board Self-Assessment | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Business | 1 |
| | | | | | 1 | | Cal | 1 |
| 8/8/23 | | 424B5 | | | | 1 | | Capitalization | 2 |
| 3/28/24 | | DEF 14A | | | | 1 | | CEO Pay Ratio | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Certain Relationships and Related Transactions, and Director Independence | 1 |
| | | | | | 1 | | Changes in and Disagreements with Accountants on Accounting and Financial Disclosure | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Compensation Committee Interlocks and Insider Participation | 1 |
| | | | | | 1 | | Compensation Committee Report | 1 |
| | | | | | 1 | | Compensation Discussion and Analysis (See separate Table of Contents) | 1 |
| | | | | | 1 | | Compensation Setting Process | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Consolidated Balance Sheets at December 31, 202 | 1 |
| | | | | | 1 | | Consolidated Statements of Cash Flows | 1 |
| | | | | | 1 | | Consolidated Statements of Comprehensive Income (Loss) | 1 |
| | | | | | 1 | | Consolidated Statements of Operations | 1 |
| | | | | | 1 | | Controls and Procedures | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Corporate Governance Guidelines | 1 |
| | | | | | 1 | | Corporate Guidelines for Business Conduct and Ethics | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Cybersecurity | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Description of Capital Stock | 3 |
| | | | | | 1 | | Description of Debt Securities | 3 |
| 8/8/23 | | 424B5 | | | | 1 | | Description of Notes | 2 |
| 2/23/24 | | S-3ASR | | | | 1 | | Description of Other Securities | 3 |
| 3/28/24 | | DEF 14A | | | | 1 | | Director Attendance at Meetings | 1 |
| | | | | | 1 | | Director Compensation | 1 |
| | | | | | 1 | | Director Terms | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Directors and Executive Officers of the Registrant | 1 |
| | | | | | 1 | | Disclosure Regarding Foreign Jurisdictions that Prevent Inspections | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Diversity and Inclusion | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Ears Ended December 31, 202 | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Election of Directors | 1 |
| | | | | | 1 | | Employment and Change in Control Agreements | 1 |
| | | | | | 1 | | Environmental Stewardship | 1 |
| | | | | | 1 | | Executive Compensation | 2 |
| 2/23/24 | | 10-K | | | | 1 | | Exhibits, Financial Statements and Financial Statement Schedules | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Experts | 3 |
| 2/23/24 | | 10-K | | | | 1 | | Financial Statements and Supplementary Data | 1 |
| | | | | | 1 | | Fis | 1 |
| | | | | | 1 | | Fiscal | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Five Percent Owners of Common Stock | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Form 10-K Summary | 1 |
| 8/8/23 | | 424B5 | | | | 1 | | Forward Looking Statements | 2 |
| 2/23/24 | | S-3ASR | | | | 1 | | Forward-Looking Statements | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Governance Policies and Practices | 1 |
| | | | | | 1 | | Grants of Plan-Based Awards for 2023 | 1 |
| | | | | | 1 | | Human Capital and Culture | 1 |
| | | | | | 1 | | Investor Outreach and Stockholder Engagement | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Item 6 | 1 |
| | | | | | 1 | | January 1 | 1 |
| | | | | | 1 | | January 2 | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Legal Matters | 3 |
| 2/23/24 | | 10-K | | | | 1 | | Legal Proceedings | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Long-Term Incentive Plan | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Management's Discussion and Analysis of Financial Condition and Results of Operations | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Mandatory Employee Training Self-Assessment | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Market for the Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities | 1 |
| 8/8/23 | | 424B5 | | | | 1 | | Material U.S. Federal Income Tax Considerations | 2 |
| 2/23/24 | | 10-K | | | | 1 | | Mine Safety Disclosures | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Monitoring Performance and Progress | 1 |
| | | | | | 1 | | Non-Qualified Deferred Compensation for 2023 | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Notes to Consolidated Financial Statements | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Option Exercises and Stock Vested for 2023 | 1 |
| | | | | | 1 | | Other Business and Information | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Other Information | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Our 2024 Director Nominees and Continuing Directors | 1 |
| | | | | | 1 | | Our Approach to Corporate Responsibility | 1 |
| | | | | | 1 | | Our Board and Its Role | 1 |
| | | | | | 1 | | Our Board Leadership Structure | 1 |
| | | | | | 1 | | Our Commitment to Integrity, Corporate Governance and Sustainability | 1 |
| | | | | | 1 | | Our Corporate Governance | 1 |
| | | | | | 1 | | Our Director Nomination Process | 1 |
| | | | | | 1 | | Outstanding Equity Awards at Fiscal Year-End | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Part I | 1 |
| | | | | | 1 | | Part Ii | 1 |
| | | | | | 1 | | Part Iii | 1 |
| | | | | | 1 | | Part Iv | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Pay Versus Performance | 1 |
| | | | | | 1 | | Pension Benefits for 2023 | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Plan of Distribution | 3 |
| 3/28/24 | | DEF 14A | | | | 1 | | Potential Payments Upon Termination | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Powers of Attorney (included on signature page) | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Principal Accountant Fees and Services | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Process for Communicating with Directors | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Properties | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Proxy Statement Summary | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Quantitative and Qualitative Disclosures About Market Risk | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Ratification of the Selection of Independent Auditors | 1 |
| | | | | | 1 | | Related Party Transactions | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Report of Ernst & Young LLP, Independent Registered Public Accounting Firm | 1 |
| | | | | | 1 | | Reserved | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Risk Factors | 4 |
| 3/28/24 | | DEF 14A | | | | 1 | | Role of Our Board, The | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Scal | 1 |
| | | | | | 1 | | Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Short-Term Incentive Program | 1 |
| 2/23/24 | | 10-K | | | | 1 | | Signatures | 1 |
| | | | | | 1 | | Statements of Changes in Consolidated Equity | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | Stock Ownership Information | 1 |
| | | | | | 1 | | Stock Ownership of Directors, Board Nominees and Executive Management | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Summary | 3 |
| 3/28/24 | | DEF 14A | | | | 1 | | Summary Compensation Table for 2023 | 1 |
| | | | | | 1 | | Table of Contents | 4 |
| | | | | | 1 | | The Role of Our Board | 1 |
| 8/8/23 | | 424B5 | | | | 1 | | Underwriting | 2 |
| 2/23/24 | | 10-K | | | | 1 | | Unresolved Staff Comments | 1 |
| 2/23/24 | | S-3ASR | | | | 1 | | Use of Proceeds | 3 |
| | | | | | 1 | | Where You Can Find More Information | 3 |
| 2/23/24 | | 10-K | | | | 1 | | Years Ended December 31, 202 | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | 1. Our Compensation Framework and Philosophy | 1 |
| 2/23/24 | | 10-K | | | | 1 | | 101 | 1 |
| | | | | | 1 | | 104 | 1 |
| | | | | | 1 | | 105 | 1 |
| | | | | | 1 | | 108 | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | 2. How We Determine Executive Compensation | 1 |
| 2/23/24 | | 10-K | | | | 1 | | 202 | 1 |
| 3/28/24 | | DEF 14A | | | | 1 | | 2024 Annual Meeting of Stockholders-Questions & Answers | 1 |
| | | | | | 1 | | 2025 Annual Meeting and Stockholder Proposals | 1 |
| | | | | | 1 | | 3. 2023 Executive Compensation Program Overview | 1 |
| | | | | | 1 | | 4. Elements of 2023 Executive Compensation Program | 1 |
| | | | | | 1 | | 5. 2023 Business and Incentive Compensation Results | 1 |
| | | | | | 1 | | 6. Total Realized Compensation | 1 |
| | | | | | 1 | | 7. Other Compensation Practices and Policies | 1 |
