COSTAR GROUP, INC.

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON TUESDAY, JUNE 23, 2026

The Board of Directors (the “Board”) of CoStar Group, Inc. (“CoStar,” “CoStar Group,” “we,” “our,” “us,” or the “Company”) solicits your proxy for use at the Annual Meeting of Stockholders (the “Annual Meeting”) to be held at 10:00 a.m., Eastern Time, on Tuesday, June 23, 2026, and at any adjournment or postponement of the Annual Meeting. The Annual Meeting will be held online only as a live webcast via the internet at www.virtualshareholdermeeting.com/CSGP2026. The webcast replay of the Annual Meeting will be made available in the Investors section of CoStar Group’s website after completion of the Annual Meeting and will remain available for a period of time following the call.

We are mailing the Notice of Internet Availability of Proxy Materials (the “Notice”) to our stockholders eligible to vote at the Annual Meeting on or about April 30, 2026. If you are a registered stockholder, to be admitted to the Annual Meeting, you will need to enter the 16-digit control number found on your Notice or proxy card. If your shares are held in brokerage accounts and your voting instruction form or the Notice indicates that you may vote those shares through the www.proxyvote.com website, then you may be admitted to the Annual Meeting using the 16-digit control number indicated on that voting instruction form or the Notice. Otherwise, stockholders who hold their shares in brokerage accounts should contact their bank, broker or other nominee (preferably at least five days before the Annual Meeting) and obtain a “legal proxy” in order to be able to attend, participate in or vote at the Annual Meeting.

The Annual Meeting will include a question and answer session, and stockholders may submit questions appropriate to our business during the Annual Meeting. Questions may be submitted during the Annual Meeting through www.virtualshareholdermeeting.com/CSGP2026. Questions pertinent to meeting matters that comply with the meeting rules of conduct will be answered during the question and answer session, subject to time constraints. However, we reserve the right to exclude questions that are not pertinent to meeting matters, irrelevant to the business of the Company, derogatory or in bad taste, or relate to pending or threatened litigation, personal grievances or are otherwise inappropriate. Questions that are substantially similar may be grouped and answered once to avoid repetition. If there are any questions pertinent to meeting matters that cannot be answered during the meeting due to time constraints, management expects to post answers to those questions on the “Investor Relations” section of the Company’s website at investors.costargroup.com as soon as practicable after the meeting.

We encourage you to access the Annual Meeting 15 minutes before it begins to avoid any delay from technical issues. If you encounter technical issues accessing the virtual Annual Meeting, you can contact the technical support number posted on the login page at www.virtualshareholdermeeting.com/CSGP2026.