$650 million

CoCounsel is Thomson Reuters' AI assistant for legal professionals, built on top of GPT-4 and integrated directly into Westlaw. It's the first legal AI product with native access to the largest verified legal database in the world — and that integration is what separates it from every general-purpose chatbot.

Originally developed by Casetext (acquired by Thomson Reuters in 2023 for $650 million), CoCounsel has evolved from a single-task tool into a multi-agent system capable of running parallel research threads, drafting documents, and analyzing contracts simultaneously.

How CoCounsel Works

CoCounsel uses a retrieval-augmented generation (RAG) pipeline connected to Westlaw's database of over 40,000 databases and billions of legal documents. When you ask a question, it doesn't just generate text — it searches verified sources, pulls relevant authorities, and constructs answers with citations you can check. The Deep Research feature launched in 2025 runs multiple AI agents in parallel, each pursuing different research angles simultaneously. One agent might search case law while another analyzes statutes and a third reviews secondary sources. The results converge into a comprehensive memo in minutes — work that would take an associate 4-8 hours.

Core Capabilities

CoCounsel handles five main workflows. Legal research: searches Westlaw and produces cited memos with pinpoint references. Document review: analyzes contracts and flags specific clauses, risks, or missing provisions. Drafting assistance: generates first drafts of briefs, motions, and correspondence. Deposition preparation: summarizes transcripts and identifies key testimony. Timeline analysis: extracts dates and events from document sets and builds chronologies. The 95%+ citation accuracy rate (when connected to Westlaw) is the number that matters. That's not a marketing claim — it's the result of RAG architecture that grounds every response in verified sources rather than generating from memory.

CoCounsel vs. Harvey vs. Claude

The three aren't interchangeable. CoCounsel is best for firms already in the Thomson Reuters ecosystem — Westlaw integration means your research AI has access to the same database your associates use. Harvey targets Am Law 100 firms and handles enterprise-scale operations (700K daily tasks). Claude is the best general-purpose option for firms that need strong drafting without enterprise pricing. CoCounsel's advantage is verified legal data. Harvey's advantage is scale and customization. Claude's advantage is price and prose quality. Most mid-size firms will pick CoCounsel because they're already paying for Westlaw.

Pricing and Access

Thomson Reuters doesn't publish fixed CoCounsel pricing — it's bundled into Westlaw subscriptions with custom quotes. Industry reports place it at $100-200/user/month as an add-on to existing Westlaw plans. The AI-assisted Westlaw tier (Westlaw Precision with CoCounsel) runs higher. Some firms report all-in costs of $300-500/user/month when combined with Westlaw Edge. The pricing strategy is lock-in: if you're already spending $150K/year on Westlaw, adding CoCounsel for an incremental $50-100K is easier to justify than switching to Harvey at $1,200+/user/month.

Limitations Managing Partners Should Know

CoCounsel is powerful but not perfect. It's tethered to Westlaw — if your firm uses LexisNexis, you're looking at a platform switch, not just an AI add-on. The multi-agent Deep Research feature sometimes produces overlapping results from parallel agents. And like all legal AI, it requires attorney verification — the 95% accuracy rate means 1 in 20 citations may need correction. The biggest limitation is practice area coverage. CoCounsel excels in litigation, corporate, and regulatory work. For niche practices (immigration, tribal law, international arbitration), the underlying Westlaw data may be thinner, which means the AI outputs are thinner too.

The Bottom Line: CoCounsel is Thomson Reuters' legal AI assistant, built on GPT-4 with native Westlaw integration. It runs multi-agent research, drafts documents, and reviews contracts with 95%+ citation accuracy. It's the strongest option for firms already in the Westlaw ecosystem — but it comes with Westlaw-level pricing.