Thomson Reuters Faces Antitrust Suit Over $650 Million Casetext Acquisition

Rubin Law Office filed the antitrust case in federal court in California, alleging that Thomson Reuters acquired Casetext and subsequently discontinued its research platform in a move that reduced competition and left legal professionals facing higher prices for research services.

The allegations and details of the lawsuit were reported by Law360 on Oct. 2. According to Law360’s report on the case, the law firm contends that the $650 million transaction violated antitrust law because Thomson Reuters bought an increasingly significant rival and then shut down its platform.

The complaint casts the transaction as a so-called killer acquisition — a deal in which an established company buys a developing competitor whose products could otherwise challenge the incumbent’s market position. The plaintiff alleges that Casetext had become an important competitive force against Westlaw, Thomson Reuters’ longstanding legal research business.

According to Law360, the lawsuit was brought in the U.S. District Court for the Northern District of California. The publication identified Thomson Reuters, Casetext, LexisNexis Legal & Professional and its parent RELX among the companies connected to the dispute.

The case centers on a legal research market that has been reshaped by generative AI and other machine-learning technologies. Casetext was an early entrant in applying artificial intelligence to legal research and developed products aimed at helping lawyers search and analyze legal materials.

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Thomson Reuters agreed to acquire Casetext for $650 million in 2023, bringing the technology company into the same corporate group as Westlaw. The new lawsuit alleges that eliminating Casetext as an independent alternative weakened the pricing pressure it had exerted on established legal research providers, according to Law360’s account.

Rubin Law Office is seeking to pursue the dispute as a proposed class action. The California firm alleges that the loss of Casetext as a lower-priced competitor forced customers toward more expensive legal research offerings.

The litigation adds another antitrust challenge involving Thomson Reuters’ position in legal research. In a separate dispute involving the now-defunct AI legal research company ROSS Intelligence, a federal court in Delaware rejected antitrust counterclaims against Thomson Reuters in 2024. Those claims had included allegations that the company improperly tied Westlaw’s collection of case law to its search technology, according to previous Law360 reporting. The court concluded that ROSS had failed to establish that the database and search functions constituted separate products and had not adequately defined the relevant markets.

The Casetext lawsuit advances a different theory: that Thomson Reuters used an acquisition rather than product bundling to neutralize a competitive threat.

The case could put a spotlight on how traditional information providers respond to AI startups capable of disrupting established subscription businesses. Legal research has historically been dominated by Westlaw and LexisNexis, while advances in generative AI have opened opportunities for newer companies to compete through alternative research and analytical tools.

For Rubin Law Office, the central allegation is that Casetext was one of those challengers — and that its acquisition removed a source of competition before it could develop into a still stronger rival.

Those assertions remain allegations and have not been adjudicated. The lawsuit’s filing does not establish that Thomson Reuters violated antitrust law.

Source: Law360