CoCounsel (by Casetext)

CoCounsel is Thomson Reuters' professional-grade generative AI legal assistant, originally built by Casetext (acquired by Thomson Reuters in 2023 for $650 million) and now deeply integrated with the Westlaw legal research ecosystem. It is designed specifically for licensed attorneys, paralegals, and in-house legal teams who need to perform substantive legal work — research, drafting, review, and analysis — at a faster pace without sacrificing the verifiability that the profession requires. Unlike general-purpose chatbots, CoCounsel is trained and tuned on Thomson Reuters' proprietary legal content, including Westlaw case law, statutes, regulations, secondary sources, and Practical Law guidance, with citations grounded in authoritative materials rather than open-web sources.

The assistant operates through a series of structured 'skills' that map to common legal workflows: legal research memos, document review across large evidence sets, contract analysis and policy comparison, deposition preparation, summarization of transcripts and filings, and timeline extraction from case materials. Each skill follows a guided input-output pattern — the attorney provides a natural language query or uploads documents, CoCounsel processes the request against its content sources, and the output includes structured findings with inline citations linked back to Westlaw authorities or the uploaded source material.

Thomson Reuters reported that Casetext had over 10,000 law firm and corporate legal department customers at the time of the $650 million acquisition in August 2023. Since the acquisition, Thomson Reuters has invested heavily in expanding CoCounsel's capabilities, integrating it across the broader Thomson Reuters legal technology stack including Westlaw Precision (which indexes over 40,000 databases of case law, statutes, and regulations), Practical Law (which contains over 90,000 regularly updated practice notes, standard documents, and checklists), Document Intelligence, and HighQ collaboration workspaces. The platform now supports CoCounsel Drafting, an embedded Microsoft Word add-in for generating first drafts of motions, briefs, contracts, and correspondence, as well as CoCounsel Core for tax, audit, and risk professionals integrated with Thomson Reuters Checkpoint.

CoCounsel's document review capability is designed to handle large-scale evidence sets — processing hundreds of thousands of pages with consistent application of legal review criteria across every document in the corpus. This is particularly valuable for litigation discovery, regulatory investigations, and due diligence workflows where manual review would require weeks of attorney time. The platform returns structured tables of findings with source citations, enabling attorneys to quickly identify privileged materials, relevant evidence, and key issues across massive document collections.

On the enterprise governance front, CoCounsel operates under SOC 2 Type II compliance, does not use customer data to train foundation models, and provides role-based access controls, matter-level data segregation, audit logging, and SSO integration. Thomson Reuters has also committed to a multi-model strategy, incorporating frontier AI models from multiple providers while keeping all retrieval grounded in its proprietary Westlaw and Practical Law content. These security and governance features are designed to meet the procurement requirements of large law firms (including AmLaw 100 and 200 firms), corporate legal departments, and government agencies that operate under strict data handling and confidentiality obligations.