By The Briefcase Team | June 19, 2026

In October 2023, a Kansas City jury decided that the National Association of Realtors and four of the biggest residential brokerages in America had conspired to keep commissions high. The verdict was $1.8 billion, trebled to $5.4 billion under antitrust law. NAR settled. Anywhere settled. Keller Williams settled. RE/MAX settled. The 6 percent commission, which had been protected by an MLS rule since the 1990s, was effectively dismantled. The biggest industry lobby in real estate lost its grip on its own pricing structure inside of 18 months.

Last Friday, June 12, a commercial tenant in Denver filed a lawsuit in federal court in Chicago against CoStar, CBRE, JLL, Cushman & Wakefield, Colliers, and Newmark. It alleges the same kind of conspiracy. Same legal theory. Same plaintiff playbook. Same set of "we exchange data to provide market transparency" defenses.

If you only read one paragraph of this email, read this one: the case against CoStar is the commercial real estate version of Sitzer/Burnett. And the plaintiffs have already done something Sitzer's lawyers spent three years trying to do, which is putting a specific number on the harm.

From the complaint, as reported by Facilities Dive:

"From 2015 to 2025, every 1-point increase in CoStar's market share corresponded to a 0.3 percent to 0.8 percent increase in rent per square foot across industrial, office, and retail leases."

CoStar's market share in commercial real estate information services has gone from roughly 50 percent to over 80 percent nationally during that decade, with metro-level dominance ranging from 58 percent to 97 percent. That is somewhere between 9 and 24 points of share gain, which works out to a rent uplift of 2.7 percent to 19.2 percent, depending on which end of the range you trust.

For context, commercial rents in major U.S. metros total well over a trillion dollars a year. The complaint doesn't say "billions in damages" the way some do. It implies them with a regression.

The legal theory is called "hub-and-spoke," and it's the same one prosecutors used against Smith Travel Research and the major luxury hotel operators in the Western District of Washington (CoStar owns STR, by the way). It's also the same theory the Maryland Attorney General is using against RealPage and a group of residential landlords.

The structure works like this. CoStar (the hub) collects sensitive lease data from brokers (the spokes). Effective rents, concessions, free-rent periods, tenant improvement allowances, all of it. The brokers submit their own data to CoStar in exchange for access to everyone else's. Each broker theoretically gains an information edge. In practice, every broker can see what every other broker is closing deals at in near-real-time, and the natural consequence is that everyone's quotes drift toward the same numbers.

From the complaint: "Through mutual monitoring enabled by CoStar, the Broker Defendants detected deviations from prevailing market rents, replacing independent pricing decisions with coordinated conduct."

If you have ever wondered why office rents in midtown Manhattan or Chicago's Loop are so eerily consistent across competing brokerages, the plaintiffs would like to suggest an answer.

This is the underreported part. The June 12 case is the third antitrust class action against CoStar filed in 2026 alone.

Case one. Shapiro Hospitalities v. CoStar, filed April 14 in the Eastern District of Virginia. 79-page complaint. Alleges CoStar locked up the three largest national brokerages with mutual non-compete agreements that prevented them from launching a competing platform.

Case two. Malm Inc. v. CoStar, filed April 15 in the Central District of California. 73-page complaint. Alleges CoStar uses watermarks and "fingerprints" embedded in listing data to detect when brokers cross-post listings to rival platforms, then enforces de facto exclusivity through retaliation.

Case three. FitFactariDC v. CoStar et al., filed June 12 in the Northern District of Illinois. 47-page complaint. The new one. Different in that it names the brokerages as co-defendants, not just CoStar.

Three different plaintiff law firms. Three different jurisdictions. Three different angles of attack. And a parallel FTC investigation that began in 2023 and has yet to formally close, in which the agency filed an amicus brief on the side of plaintiffs in a Ninth Circuit case where CoStar was the defendant.

When three independent law firms file structurally similar antitrust class actions against the same company inside of 60 days, that is not coincidence. That is convergence. The plaintiffs' bar smells what the residential plaintiffs' bar smelled in 2019, which is a verdict.

CoStar General Counsel Gene Boxer called the FitFactariDC complaint "slapdash" and "frivolous". CEO Andy Florance has not yet personally commented on the June 12 case, but in April's Q1 earnings call he characterized CoStar as "more focused" after activist investor Third Point liquidated its entire stake.

That earnings call is worth a second look. CoStar reported 60 straight quarters of double-digit revenue growth and a doubling of adjusted EBITDA year-over-year. The stock, however, was already down 47 percent year-to-date by early May, and is now trading at about $30 versus its August 2025 peak of $97. The market is pricing in something. Something that has gotten worse, not better, since April.

In Sitzer/Burnett, the defendants who settled fastest were the public brokerages. Anywhere settled. Keller Williams settled. RE/MAX settled. They settled because, in a class action of this size, the cost of going to trial and losing is existential.

CBRE, JLL, Cushman & Wakefield, Colliers, and Newmark are five publicly traded companies with combined market capitalizations north of $50 billion. Their entire business model depends on (a) maintaining access to CoStar's data and (b) charging clients for market expertise that is, in significant part, derived from that data. If the FitFactariDC plaintiffs prevail on the hub-and-spoke theory, the brokerage defendants are exposed to treble damages on top of CoStar's exposure, plus the existential question of how they reconstruct their data infrastructure if a court orders the existing arrangement dismantled.

The defense available to the brokers is, essentially, "we had no choice, we needed the data to compete." That defense did not work in the residential case. It is unlikely to work here.

If you are a commercial tenant who signed a lease in one of 49 major U.S. metropolitan areas between June 2022 and now, you are inside the proposed class definition. Whether you knew it or not, you may have just been opted into the largest commercial real estate antitrust case in U.S. history.

If you are a landlord who relied on CoStar comps to set rents, your underwriting models for the past decade just got an asterisk. The plaintiffs are alleging the comps themselves were contaminated.

If you are a commercial broker who uses CoStar, you are simultaneously a victim of the alleged conspiracy (because you paid subscription fees the plaintiffs say were supracompetitive) and a potential co-defendant if your firm is one of the five named. Pick a lane.

If you are an investor in CSGP, well, the stock has already told you what to do. It went from $97 to $30 in 10 months, lost its activist shareholder, and is now facing three concurrent antitrust class actions plus an open FTC matter. That is not a normal sequence of events.

The residential commission system that had governed how Americans bought and sold homes for 30 years was dismantled by a single Kansas City jury in 11 days of deliberations in October 2023. The commercial real estate data ecosystem that has governed how Americans price office, retail, and industrial leases for almost as long is now under coordinated legal attack from three federal courts.

The first status hearing in the FitFactariDC case is August 19. Set your calendars. The next 18 months are going to be very loud, and not for CoStar.

The free market does its job in two ways. Sometimes it does it through competition. Sometimes it does it through the courts. In commercial real estate, it looks like we are going to find out which one matters more.