Key Takeaways
- CoCounsel is an AI legal assistant, now owned by Thomson Reuters.
- It began at Casetext and was acquired by Thomson Reuters in 2023.
- It handles research, document review, summarization, and drafting.
- Great for legal teams wanting AI grounded in Westlaw authority.
CoCounsel was the legal profession’s first prominent GPT-4-powered assistant, built by Casetext and acquired by Thomson Reuters in 2023 for $650 million. It works like a capable junior associate: hand it a research question, a pile of documents to review, a deposition to summarize, or a contract to analyze. Now integrated with Westlaw’s authority, its answers are grounded in real law rather than invented — which in this field is everything.
What is CoCounsel?
CoCounsel is an AI legal assistant originally built by Casetext, which launched it in 2023 as one of the first professional applications of GPT-4, and was acquired by Thomson Reuters that year for approximately $650 million. It is now Thomson Reuters’ flagship legal AI product, integrated with Westlaw and its wider legal content. CoCounsel works through a set of legal “skills” rather than open-ended chat, including legal research memos answering questions with citations to authority, document review across large sets (asking questions of thousands of documents at once), deposition and transcript summarization, contract analysis and policy compliance checking, timeline construction from documents, and drafting assistance. Its grounding in Thomson Reuters’ validated legal content — and Westlaw’s KeyCite for checking whether authority remains good law — directly addresses the hallucinated-citation problem that has produced real court sanctions for lawyers relying on general chatbots. It targets law firms, in-house legal departments, and legal professionals. Pricing is arranged with Thomson Reuters.
What it does well
- Grounded: answers cite real authority via Westlaw.
- Skill-based: purpose-built legal tasks, not open chat.
- Document review: query thousands of documents at once.
- Proven: the first major GPT-4 legal application, now TR-backed.
Who it is for
CoCounsel fits law firms, in-house counsel, and legal professionals who want an AI assistant for research, document review, deposition summarization, and contract analysis that is grounded in genuine legal authority — a critical distinction, since general chatbots inventing case citations has led to actual court sanctions. Its purpose-built skills and Westlaw integration make it substantially safer than generic AI for legal work. Non-lawyers will not need it, it is professionally priced via Thomson Reuters, and attorney review of all output remains essential, but for legal AI, CoCounsel is an excellent choice.
Things to keep in mind
- AI legal output still requires attorney review and professional judgment.
- It is a professional platform priced via Thomson Reuters.
- Always verify cited authority — even grounded AI warrants checking.
Our verdict
CoCounsel is a leading AI legal assistant with real pedigree: built by Casetext as the first prominent GPT-4 professional application, then acquired by Thomson Reuters for around $650 million and integrated with Westlaw. Its skill-based design — research memos with citations, review across thousands of documents at once, deposition summarization, contract analysis, timeline construction — suits how legal work actually happens, and its grounding in validated authority with KeyCite validation addresses the fabricated-citation problem that has sanctioned real lawyers. Attorney review remains essential and it is professionally priced, but CoCounsel is an excellent choice.
Frequently asked questions
What is CoCounsel?
CoCounsel is an AI legal assistant offering research, document review, deposition summarization, contract analysis, and drafting, grounded in Thomson Reuters legal content.
Who owns CoCounsel?
It was built by Casetext and acquired by Thomson Reuters in 2023 for approximately $650 million; it is now their flagship legal AI product, integrated with Westlaw.
How does CoCounsel avoid fabricated citations?
It is grounded in Thomson Reuters’ validated legal content with citations to real authority, and uses Westlaw’s KeyCite to check whether authority is still good law.
Who is CoCounsel for?
It is for law firms, in-house legal departments, and legal professionals wanting AI for research, review, and drafting grounded in real legal authority.
