By Thomson ReutersLearning Objectives
- Understand what CoCounsel and Westlaw Advantage offer and how they work together
- Evaluate the Deep Research agentic AI capability for legal research
- Assess Thomson Reuters' dominant position in legal AI
- Explain why a data publisher would train its own model rather than license one
What Are CoCounsel and Westlaw Advantage?
CoCounsel is Thomson Reuters' AI legal assistant — originally built by Casetext (acquired for $650 million in August 2023) and now integrated across Thomson Reuters' entire product suite. With 1 million users across 107 countries (as of February 2026), CoCounsel is the most widely adopted AI tool in the legal profession.
Westlaw Advantage (launched August 2025) is the latest AI-powered version of Westlaw — the legal profession's definitive research platform. Its headline feature is Deep Research: agentic AI that creates multi-step research plans, executes iteratively, and delivers comprehensive reports with transparent reasoning and links to primary and secondary legal sources.
💡Key Concept
Agentic Deep Research for Law: Unlike simple AI search that returns a list of cases, Deep Research acts like a junior associate: it creates a research plan, identifies relevant statutes and case law, reads and analyzes them, identifies arguments for and against your position, verifies citations, and delivers a structured report — typically in about 10 minutes. This targets the gap between quick AI summaries and genuine legal analysis.
CoCounsel Capabilities
- Document analysis — review contracts, briefs, and filings with AI-powered extraction
- Legal research — integrated with Westlaw's authoritative case law and statutes
- Contract review — identify key terms, risks, and obligations
- Deposition preparation — analyze transcripts and identify key testimony
- Compliance monitoring — track regulatory changes and flag relevant updates
- 1 million users across legal, tax, compliance, accounting, and audit
Westlaw Advantage: Deep Research
- Creates multi-step research plans and executes them iteratively
- Produces comprehensive reports with arguments for and against
- Transparent reasoning with links to Westlaw primary/secondary sources
- Litigation Document Analyzer — analyzes opposing motions, suggests counterarguments with supporting authority
- Most comprehensive analyses complete in approximately 10 minutes
The Model Underneath
In August 2026 Thomson Reuters announced that it had trained its own model, called Thomson, and that CoCounsel Legal would be the first product to ship it. The company put the training cost at $40 million — small next to a frontier lab's budget, because Thomson is not trained from scratch. It starts from an open-source base and then applies mid-training and post-training on decades of Westlaw, Practical Law, Checkpoint and Reuters material, with hundreds of in-house lawyers, tax specialists and editors shaping the process.
Thomson Reuters says early evaluations put the model on par with current frontier models on legal and tax reasoning and instruction-following, at a fraction of their cost, and that it has used under 10 percent of its archive so far. A smaller version is published on Hugging Face for academic and non-commercial use.
💡Key Concept
Why train rather than license: most professional-software vendors point a general frontier model at their content at query time, which is retrieval. Training on the corpus instead moves that knowledge into the weights, so the domain behaviour survives without a retrieval step — and the vendor stops renting its core capability from a lab that also sells to its competitors. The trade is that the model must be maintained and re-trained as the law changes, which is a cost a licensee does not carry.
Treat the parity claim carefully. These are the vendor's own evaluations on its own domains, not an independent benchmark, and "on par on legal and tax reasoning" is a much narrower statement than general frontier parity.
Pricing
Company Details
| Detail | Info |
|---|---|
| Company | Thomson Reuters (NYSE: TRI) |
| Revenue (2025) | $7.48 billion (+7% organic growth) |
| AI Investment | $200+ million annually in productized AI |
| Capital Capacity | ~$11 billion through 2028 for AI investment and acquisitions |
| CoCounsel Users | 1 million across 107 countries |
| Casetext Acquisition | $650 million (August 2023) |
| In-House Model | Thomson — $40 million to train, announced August 2026 |
| Website | legal.thomsonreuters.com |
Key Takeaways
- CoCounsel has 1 million users in 107 countries — the most widely adopted AI legal tool, integrated across Thomson Reuters' entire suite
- Thomson Reuters trained its own model, Thomson, for $40 million on an open-source base plus decades of Westlaw and Reuters content; CoCounsel Legal ships it first, and the parity claim comes from the vendor's own evaluations
- Westlaw Advantage's Deep Research is the legal industry's first professional-grade agentic AI research tool — creating research plans, executing iteratively, and delivering structured reports
- Backed by Thomson Reuters' $7.48 billion revenue and $200+ million annual AI investment; $11 billion capital capacity for continued expansion
- CoCounsel Core starts at $225/user/month; Westlaw Advantage pricing is enterprise-custom
