This post is part of a continuing Hub and Spoke series on The Big Tech Cases. You can read more of our coverage, including on Google Search, here, here, here, here, here, and here.
CoStar Group, Inc.’s (“CoStar”) petition for Supreme Court review in its dispute with Commercial Real Estate Exchange, Inc. (CREXi) asks the justices to intervene in what it characterizes as a major doctrinal rupture in exclusive dealing and monopolization law.
A closer examination, however, suggests the decision below may be more limited that the petition implies. The Ninth Circuit applied well-established principles to a modern platform market at the pleading stage. The supposed circuit splits and doctrinal upheavals may be less about legal innovation and more about strategic reframing.
Although the case arises from competition in commercial real estate listings, it has significant implications beyond real estate: if the Supreme Court takes up this dispute, the outcome could shape how antitrust law applies to platform markets built on proprietary data and network effects.
From Copyright to Antitrust: The Proceedings Below
The litigation between CoStar and CREXi began in 2020, when CoStar sued CREXi for copyright infringement, claiming CREXi stole proprietary commercial real estate listing images and information from its databases.[1] CREXi responded with antitrust counterclaims under Sections 1 and 2 of the Sherman Act and California’s Cartwright Act.[2] CREXi alleged that CoStar built a “moat” around its customer base by imposing contract terms and technological barriers on brokers to prevent them from posting their listings anywhere else.[3] According to CREXi, these restrictions enabled CoStar to maintain its monopoly power in the commercial real estate listing market, in violation of Section 2, and to foreclose competition in that market, in violation of Section 1.[4]
The District Court for the Central District of California dismissed CREXi’s Sherman Act counterclaims at the pleading stage, and the Ninth Circuit reversed.[5] While the District Court applied a unilateral “refusal-to-deal” standard to CoStar’s alleged practice of blocking brokers from cross-listing on CREXi or other competing platforms, the Ninth Circuit held that the proper framework was “de facto” exclusive dealing by an alleged monopolist.[6] In other words, the Ninth Circuit held that the Supreme Court’s defense-friendly decision in Trinko v Verizon Communications did not apply.
The Ninth Circuit folded together its monopolization and exclusive dealing analyses. First, the Ninth Circuit held, because CREXi had adequately alleged CoStar’s monopoly power, it had also alleged CoStar’s agreements with brokers substantially foreclosed competition, as required to state an exclusive dealing claim.[7] Likewise, because CREXi had adequately pled CoStar’s broker agreements were exclusive, it had also satisfied the anticompetitive conduct element of a monopolization claim.[8]
The CoStar decision is the first time the Ninth Circuit has expressly recognized a “de facto” exclusive dealing theory for Section 1 liability, crediting CREXi’s allegations that, despite some language in CoStar’s customer agreements suggesting brokers can post their listings elsewhere, in practice, CoStar enforces exclusivity.[9] The Ninth Circuit cited as precedent Third and Eleventh Circuit decisions holding that agreements conditioning rebates and discounts on exclusivity were, in practice, exclusive agreements.[10] These “de facto” exclusive dealing cases reflect antitrust doctrine’s longstanding recognition that the anticompetitive effects of exclusionary conduct like exclusive dealing depend on market realities.
CoStar’s Framing: A “Radical” Departure from Settled Doctrine
In its petition for Supreme Court review, CoStar paints the Ninth Circuit’s decision as a drastic expansion of antitrust liability for both exclusive dealing and monopolization claims.[11]
On exclusive dealing, CoStar argues that the Ninth Circuit has exacerbated a circuit split regarding “de facto” exclusive agreements. The Second and Eighth Circuits have rejected “de facto” exclusive dealing claims, while the Third, Tenth, and Eleventh circuits have sustained exclusive dealing claims based on contracts which, while not explicitly exclusive, are exclusive in practice due to economic incentives or in combination with non-contractual policies and programs.[12]
And while other appeals courts have recognized narrow “de facto” exclusive dealing theories, CoStar argues, the Ninth Circuit has removed all guardrails by treating an explicitly non-exclusive contract as exclusive based on customer confusion.[13] According to CoStar, the Ninth Circuit’s version of “de facto” exclusive dealing creates an end run around the requirement to show that an exclusive agreement substantially forecloses competition.[14]
CoStar also faults the Ninth Circuit for treating CREXi’s allegations about “technological barriers” as part of an exclusionary scheme that also included CoStar’s agreements with brokers rather than a “straightforward” refusal to deal with its rivals.[15] CoStar claims that the Ninth Circuit’s analysis enabled CoStar to “[evade] the refusal-to-deal doctrine through creative pleading.”[16] By deferring to CREXi’s characterization of its claims, according to CoStar, the Ninth Circuit split from the Tenth Circuit and the D.C. Circuit, who have held that denying access to technological facilities like platforms or databases falls squarely within Trinko’s[17] refusal-to-deal framework.[18] According to CoStar, courts’ refusal to follow Trinko will deter large firms from innovating for fear of being forced to share successful technologies with competitors.[19]
CREXi’s Response: Applying Established Principles to Modern Markets
CREXi’s opposition urges the Court to deny review, arguing that the Ninth Circuit applied well-settled principles and that the case is a poor vehicle for the sweeping doctrinal pronouncements CoStar seeks. CREXi accuses CoStar of trying to “manufacture legal questions out of their disagreements with the court of appeals’ view of CREXi’s factual allegations at the motion to dismiss stage.”[20]
On “de facto” exclusive dealing, CREXi cites decades-old Supreme Court precedents holding that anticompetitive effect depends on market realities rather than specific contractual language.[21] Rather than a circuit split, CREXi explains, the appellate decisions CoStar cites reflect applications of the same legal principles to different sets of facts.[22] The Second and Eighth Circuits, according to CREXi, recognize “de facto” exclusive dealing claims, but found no de facto exclusivity in the cases cited by CoStar.[23] In any event, CREXi argues, the Ninth Circuit looked to the express provisions in CoStar’s broker contracts and found CREXi plausibly alleged their practical effect was to foreclose brokers from working with CoStar’s competitors. [24]
As for refusal-to-deal, CREXi argues CoStar mischaracterizes its allegations and the Ninth Circuit’s analysis, ignoring the facts alleged in its complaint.[25] CoStar does not block rivals from accessing its own website, but rather from “accessing broker-owned websites, even when brokers request that the competitor visit their sites.”[26] According to CoStar, no court of appeals–including the Ninth Circuit– would permit a refusal-to-deal claim to proceed simply because a plaintiff labelled it as exclusive dealing.[27] Rather, courts consistently look at the specific facts in each case to determine whether an alleged monopolist has unilaterally refused to deal with a rival or has entered into exclusive dealing arrangements with third parties.[28]
Finally, CREXi emphasizes that the Ninth Circuit’s decided an interlocutory appeal in the early stages of litigation, making this an inappropriate case for Supreme Court review.[29] The Ninth Circuit did not find that CoStar’s conduct was unlawful; it simply concluded that the allegations were sufficient to proceed. Because the Ninth Circuit reversed and remanded for further proceedings, the parties will have to litigate CoStar’s agreements are in fact exclusive and, if so, whether they have anticompetitive effects.[30]
Why CREXi’s Position Is Stronger
In its petition for Supreme Court review, CoStar has misconstrued the Ninth Circuit’s opinion to turn its doubt about the sufficiency of CREXi’s allegations into legal issues about. But the Ninth Circuit held only that CREXi’s allegations were sufficient to justify proceeding to discovery – not that CREXi had actually proved CoStar’s dealing was exclusive or substantially foreclosed competition in the relevant markets. CoStar appears to disregard or misrepresent CREXi’s factual allegations because it doubts CREXi will be able to substantiate its claims during discovery. But that is an issue to be worked out in discovery – not in a Supreme Court appeal on an underdeveloped record.
Will the Supreme Court Take It?
The Supreme Court grants review in a small percentage of cases and is often reluctant to intervene in interlocutory appeals absent a clear and entrenched circuit conflict. In this instance, however, the Court insisted that CREXi answer the CoStar’s petition after CREXi indicated that it would not do so. The Supreme Court’s request for CREXi’s response offers some “tea leaves” over whether the Court will grant the petition.
If review is denied, the Ninth Circuit’s opinion will stand as a pleading-stage application of established exclusive dealing and Section 2 principles to alleged, but unproven, conduct. If review is granted, the case could become a vehicle for clarifying how traditional antitrust doctrines apply in data-driven platform markets.
For now, the more restrained reading of the decision below is that it reflects an allegation-bound determination about plausibility rather than a sweeping redefinition of exclusive dealing or refusal-to-deal doctrine. Whether the Court agrees that further clarification is needed will likely determine the petition’s fate.
Implications Beyond Real Estate
Beyond commercial real estate, the case has potential implications for digital platforms more broadly. Many platform businesses rely on contractual terms, data access controls, and technical design choices that can affect how users interact with rival services. If courts treat practical restrictions—rather than formal exclusivity language—as sufficient to state an exclusive dealing claim, companies operating data-driven marketplaces may face greater scrutiny of how their agreements and product architecture function in practice. At the same time, a Supreme Court decision narrowing such theories could reinforce the primacy of formal contractual terms and refusal-to-deal limits under Trinko. Either way, the case sits within a larger debate over how traditional antitrust doctrines apply to platform ecosystems built on network effects, interoperability constraints, and proprietary data.
[1] Id. at 1064.
[2] Id.
[3] Id.
[4] See id. at 1065-66.
[5] CoStar Grp., Inc. v. Com. Real Est. Exch., Inc., 150 F.4th 1056, 1064 (9th Cir. 2025).
[6] Id. at 1072.
[7] Id at 1067.
[8] Id.
[9] Id. at 1073 (citing
[10] See ZF Meritor, LLC v. Eaton Corp., 696 F.3d 254, 281 (3d Cir. 2012), cert denied, 141 S. Ct. 2877 (2013); McWane, Inc. v. FTC, 783 F.3d 814, 819-20 (11th Cir. 2015).
[11] Petition for a Writ of Certiorari at 8, CoStar Grp., Inc. v. Com. Real Est. Exch., Inc., No. 25-667.
[12] Id. at 9-11.
[13] Id. at 14.
[14] Id. at 19.
[15] Id. at 20.
[16] Id. at 23.
[17] Verizon Commc’ns, Inc. v. Law Offices of Curtis V. Trinko, LLP, 540 U.S. 398, 124 S. Ct. 872 (2004)
[18] Id. at 23.
[19] Id. at 29.
[20] Respondent’s Brief in Opposition at 2, CoStar Grp., Inc. v. Com. Real Est. Exch., Inc., No. 25-667.
[21] Id.
[22] Id. at 3.
[23] Id. at 14-15.
[24] Id. at 7-8, 18-19.
[25] Id. at 3-4.
[26] Id. at 8.
[27] Id. at 21.
[28] See id. at 23-25.
[29] Id. at 28.
[30] See id. at 28-29.
