AI training did not justify copying: ROSS loses case over Westlaw content

The court rejected the fair use defense for legal search engine ROSS, which was trained on a competitor's editorial content.

On Sep 30, 2026, the U.S. Court of Appeals for the Third Circuit upheld a finding of copyright infringement involving 2,243 Westlaw headnotes.

What was copied. Westlaw editors write summaries, known as headnotes, for individual legal issues in court opinions. LegalEase prepared about 25,000 training examples for ROSS: a question and 4–6 excerpts from court opinions. The company used these headnotes to write the questions.

ROSS returned excerpts from a database of roughly 10 million court opinions rather than generating new text. The court found that training changed the purpose of the copied material only minimally: ROSS was building a replacement for Westlaw at comparable prices. Some law firms had already switched to ROSS.

The small share did not help. ROSS argued that it had copied only 0.08% of Westlaw's 28 million headnotes. The court treated each headnote as a separate copyrighted work. ROSS could have used the court opinions themselves for training examples, and the court did not accept the convenience of ready-made headnotes as a justification for copying.

Thomson Reuters was not yet selling licenses to use headnotes for AI training. The court still considered harm to the potential market for such licenses: a lack of sales did not mean there was no market.

The ruling upheld the infringement finding in the ROSS search engine case but did not resolve disputes over training generative AI, lawyer Aaron Moss emphasizes in his Oct 4 analysis. ROSS shut down in 2021 because of the financial burden of the litigation, and damages in the case have yet to be determined.

Original sources: [Futurism, Oct 6, 2026](https://futurism.com/artificial-intelligence/court-finds-copyrighted-material-training-data-fair-use), [Aaron Moss's analysis, Oct 4, 2026](https://copyrightlately.com/thomson-reuters-v-ross-fair-use-generative-ai/).

ROSS representatives said they intend to appeal to the U.S. Supreme Court.

AI training did not justify copying: ROSS loses case over Westlaw content

The court rejected the fair use defense for legal search engine ROSS, which was trained on a competitor's editorial content.

On Sep 30, 2026, the U.S. Court of Appeals for the Third Circuit upheld a finding of copyright infringement involving 2,243 Westlaw headnotes.

ROSS representatives said they intend to appeal to the U.S. Supreme Court.