Supreme Court Clears Path for Antitrust Scrutiny of CoStar Group’s Market Dominance

The U.S. Supreme Court declines to review CoStar's petition, clearing the way for Crexi's antitrust monopoly claims to proceed in lower court.

By: AXL Media

Published: Mar 25, 2026, 4:08 AM EDT

Source: Bisnow

Judicial Greenlight for Monopoly Allegations

The U.S. Supreme Court’s refusal to intervene on March 24, 2026, marks a pivotal moment in the long-standing legal warfare between CoStar Group and Crexi. By declining CoStar's petition, the high court effectively upholds a June 2025 ruling from the U.S. Court of Appeals for the 9th Circuit. That court determined that Crexi had provided enough evidence to suggest that CoStar’s business practices—specifically its restrictive platform access—may violate federal antitrust laws. The case will now return to the lower district court for a full examination of CoStar’s alleged monopolistic control over the commercial real estate (CRE) data market.

A Legal Conflict Rooted in Intellectual Property

The current antitrust battle is the outgrowth of a legal saga that began in 2020. Initially, CoStar sued Crexi for copyright infringement, alleging that the newer marketplace had systematically "stolen" thousands of proprietary images and data points to build its own platform. Crexi responded with a massive countersuit, arguing that CoStar uses its dominant market position to stifle competition. Specifically, Crexi claims CoStar blocks brokers from uploading listings to competing platforms and prevents cross-platform data access, which Crexi argues artificially inflates operating costs for the entire industry.

Strategic Rationale and Market Implications

CoStar’s defense rests on the principle that a private company has no legal obligation to share its hard-earned data or platform with direct competitors. The company argues that forcing such access would disincentivize future investment in proprietary data businesses. However, the 9th Circuit's ruling suggested that when a company reaches a certain level of market saturation, its "exclusionary conduct" can be viewed as a violation of the Sherman Act. This decision highlights a growing tension in the tech sector between protecting intellectual property and maintaining a competitive digital marketplace.