CoStar Group’s Founder and CEO, Andrew C. Florance, bought 83,300 shares on the open market on Aug. 4, 2026, paying $29.89 per share for a total purchase of about $2.49 million. Open-market buying matters because it involves the insider using personal funds to add to their stake at the prevailing market price, rather than receiving shares through compensation or exercising options. As the company’s founder and chief executive, Florance is among the insiders with the most direct visibility into CoStar’s operations, strategy, and competitive position. While insiders can buy for many reasons, a purchase of this size is notable because it represents a clear decision to increase exposure rather than simply hold existing equity. The fact that it was described as not being under a pre-scheduled 10b5-1 plan can make it more informative to investors, since it suggests the timing was discretionary. Over the past 30 days, this is the only reported insider transaction at CSGP. With no offsetting insider sales in the same period, the recent activity is one-sided, centered on a sizable buy by the top executive.