Material Event (Form 8-K)

Item 8.01 Other Events.

On August 21, 2026, Cabot Corporation ("Cabot") completed the issuance and sale of $350 million aggregate principal amount of 4.950% senior notes due 2029 (the "Notes").

The offering of the Notes was registered pursuant to an automatically effective shelf registration statement on Form S-3ASR under the Securities Act of 1933, as amended (Registration Statement No. 333-276078) (the "Registration Statement"), that was filed with the Securities and Exchange Commission on December 15, 2023.

The Notes were issued pursuant to an indenture (the "Base Indenture"), between Cabot and U.S. Bank Trust Company, National Association, as trustee (the "Trustee") dated as of June 22, 2022, as supplemented by the Second Supplemental Indenture (the "Second Supplemental Indenture"), dated as of August 21, 2026, between Cabot and the Trustee. Cabot is filing the Second Supplemental Indenture as Exhibit 4.2, to this Current Report on Form 8-K. In order to furnish as an exhibit for incorporation by reference into the Registration Statement, Cabot is filing the opinion of Ropes & Gray LLP relating to the validity of the Notes as Exhibit 5.1 to this Current Report on Form 8-K

Cabot intends to use the net proceeds of the offering to redeem its $250 million aggregate principal amount of 3.40% Senior Notes due September 2026, with the remainder being used for working capital and other general corporate purposes (including, at Cabot's discretion, repayment of commercial paper and amounts, if any, outstanding under its multicurrency revolving credit facility).