CENTURY ALUMINUM CO

Evaluation of Disclosure Controls and Procedures

As of December 31, 2025, we carried out an evaluation, under the supervision and with the participation of our management, including our Chief Executive Officer and Chief Financial Officer, of the effectiveness of our disclosure controls and procedures. Based upon that evaluation, our management, including the Chief Executive Officer and Chief Financial Officer, concluded that our disclosure controls and procedures were ineffective as of December 31, 2025, because of a material weakness in internal controls over financial reporting described in Management’s Report on Internal Control Over Financial Reporting below.

Management's Report on Internal Control over Financial Reporting

Management is responsible for establishing and maintaining an adequate system of internal control over financial reporting for the Company. This system is designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. Because of its inherent limitations, a system of internal control over financial reporting can provide only reasonable assurance and may not prevent or detect misstatements. Further, because of changes in conditions, effectiveness of internal control over financial reporting may vary over time. Our system of internal control contains self-monitoring mechanisms, and actions are taken to correct deficiencies as they are identified.

As required by Section 404 of the Sarbanes-Oxley Act, management conducted an evaluation of the effectiveness of the system of internal control over financial reporting for the year ended December 31, 2025. Management’s evaluation was based on the framework in Internal Control - Integrated Framework (2013) issued by the Committee of Sponsoring Organizations (COSO) of the Treadway Commission. Based on this evaluation, management concluded that our system of internal control over financial reporting was not effective as of December 31, 2025.

A material weakness is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that there is a reasonable possibility that a material misstatement of the company’s annual or interim financial statements will not be prevented or detected on a timely basis.

We identified deficiencies in the design and operating effectiveness of (1) business process level controls at our Jamalco joint venture, including reconciliation controls and insufficient review controls related to inventories, accounts payable, accrued expenses, cost of goods sold and property, plant, and equipment, and (2) financial reporting controls over the consolidation of the Jamalco joint venture. These deficiencies constitute a material weakness in internal control over financial reporting which remains unremediated at December 31, 2025.

Notwithstanding the material weakness, management believes the consolidated financial statements included in this Annual Report on Form 10-K present fairly, in all material respects, the Company’s financial condition, results of operations and cash flows as of and for the periods presented in accordance with U.S. GAAP.

The effectiveness of our internal control over financial reporting has been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report which appears in Part II, Item 8 of this Annual Report on Form 10-K.

Remediation Plan for Material Weakness

Management, with the oversight of the Audit Committee of our Board, has dedicated resources and efforts to improve our internal controls over financial reporting and has taken the following actions towards remediating the material weakness:

•Designed and implemented controls over information technology general controls to enhance the reliability of information derived from information systems at Jamalco.

•Designed new and enhanced existing account reconciliation controls including controls to reconcile source data across accounts and additional review procedures within account reconciliations.

•The Company appointed new individuals in key roles including accounting and IT department heads.

•Enhanced training was provided to individuals responsible for account reconciliations and their review and those responsible for the consolidation of the Jamalco joint venture.

Management has implemented the remediation steps outlined above; however, management is unable to conclude the controls designed and implemented to address the material weakness are operating effectively until the applicable controls operate for a sufficient period of time. Management anticipates that remediation activities will be completed during fiscal year 2026.

Previously Reported Material Weakness

As of December 31, 2024, our management had identified a deficiency in the design of internal control over financial reporting related to information technology general controls in the areas of logical access controls including provisioning, deprovisioning, privileged access, user access review, application changes and monitoring related to Jamalco. In response to the identified material weakness, during the year ended December 31, 2025, management, with the oversight of the Audit Committee of the Board of Directors, took actions to remediate this material weakness in internal control over financial reporting.

Changes in Internal Control over Financial Reporting

Except for the remediation efforts related to the previous material weaknesses referred to above, during the three months ended December 31, 2025, there were no changes in our internal control over financial reporting that materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.