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US appeals court upholds Thomson Reuters’ landmark win in AI training lawsuit

By Thomson Reuters Sep 29, 2026 | 12:33 PM

By Blake Brittain

Sept 29 (Reuters) – A US appeals court on Tuesday upheld a ruling for information services company Thomson Reuters in its copyright dispute with former legal-research rival Ross Intelligence over Ross’ alleged misuse of copyrighted material ​to train an AI-powered legal search engine.

The Philadelphia-based 3rd US Circuit Court ‌of Appeals rejected Ross’ argument that its search engine made fair use of material from Thomson Reuters’ Westlaw platform, a first-of-its-kind ruling by a US appeals court in a wave of high-stakes copyright cases over AI training.

The appeals court’s reasoning for its decision is currently sealed.

Spokespeople and an attorney ‌for ​Ross did not immediately respond to requests for comment.

A ⁠Thomson Reuters spokesperson said the ⁠company was pleased with the ruling and “firmly believes that respecting copyright is essential for fostering innovation while protecting the intellectual property that fuels fiduciary-grade AI solutions.”

Thomson Reuters is the parent company of Reuters News.

Thomson Reuters’ 2020 lawsuit accused legal ​research company Ross Intelligence of copying Westlaw’s “headnotes,” which summarize points of law in court opinions. It accused Ross of misusing thousands of headnotes to train its ⁠competing AI-based legal search engine.

Ross shut down its platform ⁠in 2021, citing the costs of Thomson Reuters’ litigation.

Authors, news ​outlets, music labels and others have filed dozens of lawsuits against tech companies over the ​unauthorized use of copyrighted works to train AI systems. Thomson Reuters’ ‌case is the first copyright dispute over AI training to be heard by a US appeals court, though unlike those disputes, Thomson Reuters’ case does not involve generative AI — artificial intelligence that creates new content.

Ross allegedly used Thomson Reuters’ headnotes to train ⁠its search engine to identify relevant court opinions in response to user queries. The company argued that its AI training made fair use of the headnotes, raising a pivotal ⁠defense for legal disputes ‌over AI training.

Tech companies have argued that generative AI systems ⁠make fair use of the copyrighted material they are trained ​on ‌by transforming it into something new, while copyright owners say ​the companies ⁠use their work to generate competing content that threatens their livelihoods.

A federal judge in Delaware federal court rejected Ross’ fair use defense last year, prompting Ross’ appeal.

“Ross took the headnotes to make it easier to develop a competing legal research tool,” the judge said. “So Ross’s use is not transformative.”

(Reporting by Blake Brittain in Washington; Editing by Alexia ​Garamfalvi and Daniel Wallis)