Material Agreement (Form 8-K)

Item 1.01. Entry into a Material Definitive Agreement

On October 2, 2025, COPT Defense Properties, L.P. ("CDPLP"), the operating partnership of COPT Defense Properties ("CDP"), consummated the offering of $400.0 million aggregate principal amount of its 4.500% Senior Notes due 2030 (the "Notes"). The Notes are fully and unconditionally guaranteed by CDP (the "Guarantee"). The offering of the Notes and the Guarantee were registered under the Securities Act of 1933, as amended (the "Securities Act"), pursuant to the registration statement on Form S-3ASR (File Nos. 333-286440 and 333-286440-01) filed by CDP and CDPLP with the Securities and Exchange Commission on April 8, 2025 (the "Registration Statement"), including a base prospectus, dated April 8, 2025, and a prospectus supplement, dated September 23, 2025, filed with the Securities and Exchange Commission on September 25, 2025.

The terms of the Notes and the Guarantee are governed by the: (1) senior indenture, dated as of April 8, 2019, by and among CDPLP, as issuer, CDP, as guarantor, and U.S. Bank Trust Company, National Association (as successor in interest to U.S. Bank National Association), as trustee (the "Base Indenture"), as supplemented and amended by a fifth supplemental indenture thereto, dated as of October 2, 2025 (the "Fifth Supplemental Indenture," and together with the Base Indenture, the "Indenture"); and (2) Guarantee dated as of October 2, 2025.

A copy of the Base Indenture was previously filed as Exhibit 4.1 to the Registration Statement and is incorporated by reference herein. The Form of the Notes and the Fifth Supplemental Indenture are filed as Exhibits 4.1 and 4.2 hereto, respectively, and are incorporated herein by reference.