COST: Leadership change · Other company developments

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On November 7, 2026, Helena B. Foulkes notified the Board of Directors (the “Board”) of Costco Wholesale Corporation (the “Company”) of her decision to resign from the Board and all committees of the Board of which she is a member, effective November 7, 2026. She served on the Board since August 16, 2023 and was a member of the Audit Committee and the Nominating and Governance Committee. Ms. Foulkes’ resignation was not due to any disagreement with the Company on any matter relating to the Company’s operations, policies, or practices. She was recently elected governor of the State of Rhode Island. The Company and the Board express their deepest gratitude to Ms. Foulkes for her service on the Board. Item 8.01. Other Events. On November 10, 2026, the Board of Directors declared a special cash dividend on the Company's common stock of $30 per share, payable December 4, 2026, to shareholders of record at the close of business on November 24, 2026. A copy of the press release is attached as Exhibit 99.1. Item 9.01. Financial Statements and Exhibits (d) Exhibits. 99.1. Press release dated November 10, 2026. 104 Cover Page Interactive Data File (embedded within the Inline XBRL document). SIGNATURE Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized. COSTCO WHOLESALE CORPORATION Dated: November 10, 2026 By: /s/ John Sullivan John Sullivan Executive Vice President, General Counsel and Secretary