CoStar's attempt to weigh in on Zillow's antitrust fight against MRED and Compass hit a wall this week. An Illinois federal judge denied CoStar's request to file an amicus curiae brief, blocking the real estate data giant from offering its perspective to the court ahead of a July hearing.
The case centers on Zillow's claims that MRED, Chicago's multiple listing service, and Compass, the brokerage firm, engaged in anticompetitive behavior. Zillow alleges the pair conspired to restrict its access to MLS data, effectively freezing it out of a crucial market. CoStar, which competes directly with Zillow in real estate information services, sought permission to submit arguments supporting its competitor's position.
The denial matters because CoStar represents a major industry player with firsthand knowledge of how MLS data access shapes competition. By blocking CoStar's brief, the judge limited the court's exposure to testimony from a firm that depends on MLS data for its own business operations. This narrows the scope of arguments the judge will consider before the July hearing.
For brokers and agents relying on MRED, the case outcome will determine whether data remains concentrated or flows more freely to competing platforms. If Zillow wins, agents may gain better tools for comparative market analysis outside MRED's ecosystem. If MRED and Compass prevail, the status quo holds. The stakes extend beyond Chicago. MLS systems nationwide face similar scrutiny over data access policies, and this Illinois case could reshape how information flows across the industry.
Compass has significant exposure here. The brokerage operates thousands of offices nationwide and depends on agent retention. Restricted data access to competitors could become a selling point for staying with Compass. MRED, which serves roughly 50,000 agents across Illinois and Indiana, controls information that fu