Company: CENX
Filing Date: 2025-11-21
Form Type: 8-K/A
Source: 0001628280-25-053603
Chunk: 0

Company: CENTURY ALUMINUM CO
Filing Date: 2025-11-21
Form: 8-K/A
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### WASHINGTON, D.C. 20549

#### FORM 8-K/A
<div align='center'>(Amendment No. 1)</div>

### CURRENT REPORT
<div align='center'>Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of report (Date of earliest event reported): November 6, 2025</div>

#### Century Aluminum Company
<div align='center'>(Exact Name of Registrant as Specified in Charter)</div>

| Delaware                                       |     | 001-34474               |     | 13-3070826                       |
| (State or Other Jurisdiction of Incorporation) |     | -Commission File Number |     | -IRS Employer Identification No. |

| One South Wacker Drive                                        |     |      |     60606 |
| Suite 1000                                                    |     |      | -Zip Code |
| Chicago,Illinois                                              |     |      |           |
| (Address of Principal Executive Offices)                      |     |      |           |
|                                                               |     | -312 |  696-3101 |
| (Registrant's telephone number, including area code)          |     |      |           |
| N/A                                                           |     |      |           |
| (Former Name or Former Address, if Changed Since Last Report) |     |      |           |

| Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: |     |                                                                                                          |
| ☐                                                                                                                                                                           |     | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)                    |
| ☐                                                                                                                                                                           |     | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)                   |
| ☐                                                                                                                                                                           |     | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))   |
| ☐                                                                                                                                                                           |     | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR   240.13e-4(c)) |

Securities registered pursuant to Section 12(b) of the Act:

| Title of each class:                    |     | Trading Symbol