Thomson Reuters Unveils Proprietary LLM to Slash AI Costs
Thomson Reuters launches Thomson, a proprietary LLM trained on Westlaw and Practical Law data. CEO says early evaluations match frontier models at lower cost. The model powers CoCounsel, already used by 1 million professionals.
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Thomson Reuters launched a proprietary large language model built and trained on decades of its legal and tax content, the company said in an Aug. 24 press release. Dubbed "Thomson," the LLM started from an open-source foundation and was then trained on content from Westlaw, Practical Law, Checkpoint and Reuters, according to the release.
The company keeps full control of Thomson and does not face the inference costs typical of frontier models. Thomson Reuters also said it does not use customer data to train the model without explicit consent, a detail aimed at professionals who operate under duties of care and accountability.
Chief Executive Officer Steve Hasker said Thomson Reuters initially put Thomson to work in CoCounsel Legal. He described plans to add capabilities across the legal and tax portfolio and to offer sovereign AI options.
"Thomson proves what's possible when you build AI on decades of proprietary content and editorial expertise," Hasker said. "That's an advantage only Thomson Reuters has, and it shows in the results: our early evaluations put Thomson on par with the latest frontier models across a range of tasks."
Chief Technology Officer Joel Hron said the model shows there is an alternative to "bigger models, more compute, more money."
"Start with a strong foundation, specialize it deeply for the work that matters, and you can build intelligence that is highly capable, far more efficient and entirely under your control," Hron said. "We think that changes the economics of professional AI."
The launch follows a March 2024 Financial Times interview in which Hasker said Thomson Reuters had amassed $8 billion to invest in AI and had transformed from a content provider into a "content-driven" tech company. The company debuted CoCounsel, an AI platform for professional workflow automation, in June 2025. By February 2026, CoCounsel had been adopted by 1 million professionals across 107 countries.
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