CoStar Group, Inc.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On June 23, 2026, at the Annual Meeting of Stockholders (the “Annual Meeting”) of CoStar Group, Inc. (the “Company” or “our”), the stockholders of the Company, upon the recommendation of the Board of Directors of the Company (the “Board”), approved the CoStar Group, Inc. 2026 Employee Stock Purchase Plan (the “2026 ESPP”), which was approved by the Board on April 27, 2026 and became effective upon stockholder approval at the Annual Meeting. The 2026 ESPP replaces the Company’s Second Amended and Restated Employee Stock Purchase Plan (the “2021 ESPP”), and no further shares will be issued pursuant to the 2021 ESPP. The 2026 ESPP authorizes the issuance of 2,500,000 shares of the Company’s common stock. A more detailed description of the material terms of the 2026 ESPP was included in the Company’s Definitive Proxy Statement on Schedule 14A (the “Proxy Statement”) filed with the Securities and Exchange Commission on April 30, 2026. The foregoing and the summary in the Proxy Statement are not complete summaries of the terms of the 2026 ESPP and are qualified by reference to the text of the 2026 ESPP, which is included as Exhibit 10.1 hereto and is incorporated by reference herein.

Item 5.07 Submission of Matters to a Vote of Security Holders. The following items, which are more fully described in the Proxy Statement, were submitted to a vote of the stockholders of the Company at the Annual Meeting. The final voting results are as follows: 1. Each of the following nominees was elected to our Board to serve until the Company’s 2027 Annual Meeting of Stockholders or until his or her successor is elected and qualified: Louise S. Sams, Andrew C. Florance, John L. Berisford, Angelique G. Brunner, Rachel C. Glaser, John W. Hill, Christine M. McCarthy, and Robert W. Musslewhite. Name Votes For Votes Against Abstentions Broker Non-Votes ──────────────────────────────────────────────────────────────────────────────────────────────────── Louise S. Sams 339,006,366 21,916,539 137,272 9,772,170 Andrew C. Florance 359,034,877 1,924,104 101,196 9,772,170 John L. Berisford 354,126,137 6,332,305 601,735 9,772,170 Angelique G. Brunner 354,456,998 6,495,209 107,970 9,772,170 Rachel C. Glaser 357,314,132 2,366,072 1,379,973 9,772,170 John W. Hill 353,842,997 6,744,956 472,224 9,772,170 Christine M. McCarthy 357,893,033 1,785,174 1,381,970 9,772,170 Robert W. Musslewhite 342,052,457 18,894,048 113,672 9,772,170 2. The appointment of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2026 was ratified upon the following vote: Votes For 351,556,365 Votes Against 18,902,666 Abstentions 373,316 Broker Non-Votes — 3. The advisory resolution to approve the Company's executive compensation was approved upon the following vote: Votes For 257,665,608 Votes Against 103,277,424 Abstentions 117,145 Broker Non-Votes 9,772,170 4. The 2026 ESPP was approved upon the following vote: Votes For 359,953,752 Votes Against 779,358 Abstentions 327,067 Broker Non-Votes 9,772,170

Item 7.01 Regulation FD Disclosure. On June 25, 2026, the Company issued a press release (the “Press Release”) announcing the voting results from the Annual Meeting. A copy of the Press Release is attached hereto as Exhibit 99.1 and is incorporated by reference herein. The information contained in this Item 7.01 and the Press Release shall be considered “furnished” and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, nor shall it be deemed incorporated by reference into any reports or filings with the Securities and Exchange Commission, whether made before or after the date hereof, except as expressly set forth by specific reference in such a filing.