What Is CoCounsel? Thomson Reuters’ Legal AI Explained

What is CoCounsel? CoCounsel is the generative AI assistant Thomson Reuters sells to lawyers for research, document review and drafting, grounded in its Westlaw and Practical Law content. It began as a product of the legal tech company Casetext, which Thomson Reuters bought in 2023, and it now comes in several tiers with names that confuse many buyers.

This explainer covers where CoCounsel came from, what the current products include according to Thomson Reuters’ own pages, and what to ask before buying. It does not cover what CoCounsel costs in detail; see our guide to what legal AI tools cost for the reported figures.

Where CoCounsel Came From

Thomson Reuters completed its acquisition of Casetext on August 17, 2023, for $650 million in cash. The release described Casetext as founded in 2013, with customers including more than 10,000 law firms and corporate legal departments, and named CoCounsel as a key product: “an AI legal assistant powered by GPT-4” for document review, legal research memos, deposition preparation and contract analysis.

Three months later, on November 15, 2023, Thomson Reuters announced CoCounsel Core as the commercial offering of the legacy CoCounsel skills, alongside AI-Assisted Research on Westlaw Precision. The release said Thomson Reuters would build on “the AI assistant experience Casetext created with CoCounsel.” That is why some older articles say CoCounsel Core and newer pages do not.

What CoCounsel Includes Today

Thomson Reuters’ product pages now use two main names for legal customers. The CoCounsel Legal page describes the full assistant: from a single query it handles research, analysis and drafting, builds a step-by-step plan the user can inspect, and reasons from Westlaw content, Practical Law guidance spanning more than 100 jurisdictions and the organization’s own knowledge. It keeps documents, templates and matter history in one place. It lists connections to iManage, SharePoint, HighQ, Smokeball and Box, use inside Word, Outlook and Teams, and a CoCounsel Legal MCP for working within Claude.

CoCounsel Essentials is the narrower tier. The Westlaw Advantage page describes it as automating document analysis, review and drafting, and Thomson Reuters sells it bundled with Westlaw Advantage and with Practical Law. So a lawyer who says “we have CoCounsel” may mean the full CoCounsel Legal assistant or an Essentials bundle attached to Westlaw.

For the wider field, our Harvey vs. Legora guide covers the two largest independent platforms.

What to Ask Before Buying

Start with the tier. Ask in writing whether the quote is for CoCounsel Legal or an Essentials bundle, which content sets are included, and whether Westlaw Advantage is part of the deal.

Ask about terms. Thomson Reuters’ online plans page sells CoCounsel Legal on one-, two- and three-year terms and says new features are added to plans as they become available during the initial term. It does not show prices outside its configurator.

Ask about accuracy and data. The Stanford study of legal AI tools, which tested Thomson Reuters’ Westlaw and Practical Law AI products in 2024, found hallucination rates between 17% and 33% across the legal tools it tested. Those were earlier products, but the lesson stands: plan for review. Ask how prompts and documents are retained and whether they are used for training. Our guide to ABA Formal Opinion 512 explains why those answers matter for confidentiality.

Common Questions

Who owns CoCounsel?

Thomson Reuters. It acquired Casetext, the company that built CoCounsel, for $650 million in 2023.

What is CoCounsel Core?

The name Thomson Reuters gave in November 2023 to the commercial offering of the original CoCounsel skills. Current pages focus on CoCounsel Legal and CoCounsel Essentials.

What is CoCounsel on Westlaw?

Thomson Reuters sells Westlaw Advantage with CoCounsel Essentials, which adds AI document analysis, review and drafting to its Westlaw research product.

Does Thomson Reuters publish CoCounsel prices?

Not as a public list. Prices sit inside an online configurator. Reported figures are covered in our pricing guide.

The Verdict

Real. CoCounsel is a mature product backed by Westlaw and Practical Law content, and the integrations listed on its page are broad. The confusion is in the packaging, so get the exact tier, content and term in writing before comparing it with anything else.