Company: COST
Filing Date: 2025-12-04
Form Type: DEFA14A
Source: 0000909832-25-000160
Chunk: 0

Company: COSTCO WHOLESALE CORP /NEW
Filing Date: 2025-12-04
Form: DEFA14A
Chunk 0
---
### 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
<div align='center'>(Amendment No. )</div>

#### _____________________________

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)) |

| ☐ |     | Definitive Proxy Statement |

| ☒ |     | Definitive Additional Materials |

| ☐ |     | Soliciting Material under §240.14a-12 |

#### Costco Wholesale Corporation
<div align='center'>(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</div>

Payment of Filing Fee (Check the appropriate box):

| ☒ |     | No fee required |

| ☐ |     | Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11 |

| ☐ |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |