CENTURY ALUMINUM CO 10-Q

Item 4. Controls and Procedures Evaluation of Disclosure Controls and Procedures As of June 30, 2026, we carried out an evaluation, under the supervision and with the participation of our management, including our Chief Executive Officer and Principal Financial Officer, of the effectiveness of our disclosure controls and procedures. Based upon that evaluation, our management, including the Chief Executive Officer and Principal Financial Officer, concluded that our disclosure controls and procedures were not effective as of June 30, 2026. Previously Reported Material Weakness in Internal Control over Financial Reporting Management is responsible for establishing and maintaining adequate internal control over financial reporting as defined in Exchange Act Rule 13a-15(f) and 15d-15(f) based on the criteria established in Internal Control-Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission ("the COSO Framework"). As reported in our Form 10-K for the fiscal year ended December 31, 2025, we did not maintain effective internal control over financial reporting as of December 31, 2025 as a result of a material weakness related to deficiencies identified in business process level controls at our Jamalco joint venture and financial reporting controls over the consolidation of the Jamalco joint venture. A material weakness (as defined in Rule 12b-2 under the Exchange Act) is a deficiency, or combination of deficiencies, in internal control over financial reporting such that there is a reasonable possibility that a material misstatement of our annual or interim financial statements will not be prevented or detected on a timely basis. Refer to our 2025 Form 10-K for a description of our material weakness. Ongoing Remediation Efforts to Address Material Weakness Our material weakness was not remediated as of June 30, 2026. Management is committed to maintaining a strong internal control environment. Management has implemented measures designed to ensure that previously identified control deficiencies contributing to the material weakness are remediated, such that these controls are designed, implemented, and operating effectively. The remediation actions include: (i) designed and implemented controls over information technology general controls to enhance the reliability of information derived from information systems at Jamalco, (ii) designed new and enhanced existing account reconciliation controls including controls to reconcile source data across accounts and additional review procedures within account reconciliations, (iii) appointed new individuals in key roles including accounting and IT department heads, and (iv) enhanced training provided to individuals responsible for account reconciliations and their review and those responsible for the consolidation of the Jamalco joint venture. 38 Table of Contents We intend to remediate the material weakness as soon as possible; however, the material weakness will not be considered remediated until the applicable controls operate for a sufficient period of time and management has concluded, through testing, that the appropriate controls are operating effectively. Changes in Internal Control over Financial Reporting Other than the changes associated with the material weakness and remediation actions noted above, there have been no changes in our internal control over financial reporting during the three months ended June 30, 2026 that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting. 39 Table of Contents PART II – OTHER INFORMATION