Last updated: 23 October 2026. This review explains what Thomson Reuters’ CoCounsel Legal does, what it connects to, how it is sold and where it falls short, based on Thomson Reuters’ own announcements and independent research. It is general information, not legal or purchasing advice.
Short answer: CoCounsel is Thomson Reuters’ AI assistant for lawyers. In 2026 its main product, CoCounsel Legal, combines agentic research grounded in Westlaw and Practical Law with drafting, document review and citation checking, and it now plugs into Microsoft Word, Claude and other tools. It is strong on content and integration, but pricing is quote-based and every output still needs a lawyer’s review.
Key takeaways
- CoCounsel began as a GPT-4 assistant built by Casetext, which Thomson Reuters bought for $650 million in cash in August 2023.
- The next generation of CoCounsel Legal became generally available in the US on 20 August 2026, adding Westlaw Brief Builder, Workspaces, a Drafting Agent in Word and Deep Research Verify.
- Thomson Reuters does not publish a standard price. Firms get a quote, and the company offers a 24-hour free trial with no credit card.
- Independent testing has found errors in earlier Thomson Reuters AI research tools, and ABA Formal Opinion 512 makes clear that lawyers remain responsible for checking AI output.
What is CoCounsel?
CoCounsel started life at Casetext, a legal research company founded in 2013. When Thomson Reuters completed its acquisition of Casetext on 17 August 2023, it described CoCounsel as “an AI legal assistant powered by GPT-4” that handled document review, research memos, deposition preparation and contract analysis. The price was $650 million in cash.
Since then Thomson Reuters has made CoCounsel the brand for AI across its professional products. The legal version, CoCounsel Legal, was announced in August 2025 as a single product that brought together legal research, workflow automation, document search and an AI assistant. It now sits on top of the two content sets most US and UK lawyers already know: Westlaw for primary law and Practical Law for know-how, precedents and practice notes.
Thomson Reuters says one million professionals across 107 countries and territories use CoCounsel. That figure covers all CoCounsel products, not only the legal one, and it comes from the company itself.
What can CoCounsel Legal do in 2026?
The biggest change this year is the move from a chat assistant to what Thomson Reuters calls an agentic system: one that plans a multi-step task, picks the right tool and shows its reasoning. On 20 August 2026 the company announced general availability of the next generation of CoCounsel Legal in the United States. The main features are below.
| Feature | What Thomson Reuters says it does |
|---|---|
| Deep Research | Builds a multi-step research plan, shows its reasoning and delivers a cited report drawn from Westlaw and Practical Law, using tools such as KeyCite and Key Numbers |
| Deep Research Verify | Checks whether the cited Westlaw and Practical Law authority supports specific legal assertions |
| Westlaw Brief Builder | Takes a litigator from research to a first-draft brief, with the lawyer keeping control of strategy and final decisions |
| Drafting Agent in CoCounsel for Word | Drafts, edits and reviews agreements inside Microsoft Word from plain-language instructions, using Practical Law and the firm’s own precedents and playbooks |
| Tabular Analysis | Reviews up to 10,000 documents against up to 100 questions and shows the answers in a table that can be filtered and sorted |
| Workspaces | A space for each matter that holds the firm’s documents, precedents and know-how so that context carries across the team |
| Guided workflows | A growing library of step-by-step task flows for common work, with human review built into each step |
Tabular Analysis runs on Thomson Reuters’ own legal language model, which it calls “Thomson”. Other parts of the product are built on Anthropic’s Claude Agent SDK, so CoCounsel is not tied to a single model provider.
What does CoCounsel connect to?
Thomson Reuters’ strategy in 2026 is to let lawyers reach CoCounsel from whichever tool they already work in. The main connections announced so far are:
- Microsoft 365 and document management systems. The January 2026 UK launch release listed Microsoft 365, document management systems and Thomson Reuters’ own HighQ platform as integrations.
- Claude. On 12 May 2026 Thomson Reuters and Anthropic announced a Model Context Protocol (MCP) connection that lets users move work between Claude and CoCounsel Legal. Our news report on the Claude integration covers the detail.
- ChatGPT Enterprise. In September 2026 Thomson Reuters put HighQ inside ChatGPT Enterprise and began previewing a CoCounsel Legal experience there, as we reported in our story on the OpenAI tie-up. No launch date has been given for the full CoCounsel version.
- Reveal and AWS. From October 2026, reviewed evidence can move from the Reveal e-discovery platform into CoCounsel Legal without a manual export. A connection to Amazon Quick and other AWS services has been announced without a date.
Thomson Reuters says customer data is not used to train third-party models and is not shared outside the customer’s own environment. Firms should still confirm those terms in their own contract.
How much does CoCounsel cost?
There is no public price list. Thomson Reuters sells CoCounsel Legal by subscription and quotes each firm or legal department directly, and review sites such as G2 list pricing as “available upon request”. In practice the price depends on the size of the team and which content and features are included, since Deep Research draws on Westlaw and Practical Law.
For a first look, Thomson Reuters offers a 24-hour free trial of CoCounsel Legal. The trial page says no credit card is needed and that the clock starts at first login, so it is worth preparing real (non-confidential) test questions in advance. Our guide to what legal AI actually costs explains the line items to ask about, and our legal AI pilot guide sets out how to test a tool properly before signing.
Where is CoCounsel Legal available?
The US gets new features first. The next generation of CoCounsel Legal launched in the US in August 2026, and Thomson Reuters said Canada, the United Kingdom and Australia were expected later in the year.
The UK already has an earlier version. On 26 January 2026 Thomson Reuters launched CoCounsel Legal in the UK, with Deep Research on Westlaw Advantage and Practical Law. At that point Tabular Analysis was not yet available in the UK. UK buyers should ask which features are live for English and Welsh law on the date they sign.
What are CoCounsel’s limits?
The main risk with any legal AI tool is a confident answer that is wrong. Grounding a model in Westlaw and Practical Law reduces that risk, but it does not remove it.
The best known independent test is a 2024 study by researchers at Stanford RegLab and Stanford HAI. Their benchmarking of legal research tools found that Lexis+ AI and Thomson Reuters’ Ask Practical Law AI gave incorrect information more than 17% of the time, and Westlaw AI-Assisted Research more than 34% of the time. Those were earlier products, tested before CoCounsel Legal and Deep Research existed, so the numbers do not describe today’s tool. They do show why verification matters.
Thomson Reuters itself seems to accept the point. Deep Research Verify exists to check whether cited authority supports a proposition, and the company describes its approach as “Fiduciary-Grade AI”. That label is Thomson Reuters’ own description, not an independent standard.
Other practical limits are worth noting:
- The best features depend on Thomson Reuters content, so a firm that relies on other research platforms gets less value.
- Feature sets differ between countries, and new tools reach the US first.
- Agentic workflows still need a lawyer to frame the question well and to check each step.
Do lawyers still have to check CoCounsel’s work?
Yes. In the US, the American Bar Association’s Formal Opinion 512, issued on 29 July 2024, applies the existing ethics rules to generative AI. Lawyers must understand the tools they use well enough to be competent, protect client confidences, keep clients informed, and charge reasonable fees. The opinion allows billing for time spent reviewing AI output for accuracy, but says a lawyer should not charge a client to learn how to use the tool. Our explainer on ABA Formal Opinion 512 walks through each duty.
Courts are enforcing this. Our analysis of 2,006 AI hallucination cases shows how often fabricated or misdescribed authority now reaches judges, and the professional consequences that follow. Using a premium tool does not move responsibility from the lawyer to the vendor.
How does CoCounsel compare with other legal AI tools?
CoCounsel’s main advantage is content. A firm already paying for Westlaw and Practical Law gets AI that reasons over sources its lawyers trust, with KeyCite signals built in. Harvey, its best known rival, is a broad AI platform that gets much of its research content through a strategic alliance with LexisNexis announced in June 2025; our Harvey AI review compares the two approaches. For a wider view of research platforms, including LexisNexis and newer challengers, see our guide to legal research in the AI era.
In short, CoCounsel suits firms and legal departments that are already Thomson Reuters customers and want AI inside their existing research and drafting stack. Firms that use different content providers, or that want one AI layer across many vendors, should run a side-by-side pilot before committing.
Frequently asked questions
Who owns CoCounsel?
Thomson Reuters owns CoCounsel. It was originally built by Casetext, which Thomson Reuters bought for $650 million in cash in a deal that closed on 17 August 2023. CoCounsel is now the brand for Thomson Reuters’ AI assistants across legal, tax and other professional products.
Is CoCounsel free?
No. CoCounsel Legal is a paid subscription and pricing is quoted to each customer. Thomson Reuters offers a 24-hour free trial that does not require a credit card, and the trial clock starts when you first log in.
What AI model does CoCounsel use?
It uses more than one. Thomson Reuters says the next generation of CoCounsel Legal is built on Anthropic’s Claude Agent SDK, while Tabular Analysis runs on its own legal language model, called “Thomson”. The original 2023 CoCounsel was powered by GPT-4.
Is CoCounsel available in the UK?
Yes. CoCounsel Legal launched in the UK in January 2026 with Deep Research on Westlaw Advantage and Practical Law. The next-generation release that went live in the US in August 2026 was expected in the UK, Canada and Australia later in 2026.
Does CoCounsel make mistakes?
It can. All generative AI tools can produce wrong or unsupported answers, and a 2024 Stanford study found errors in earlier Thomson Reuters research tools. Features such as Deep Research Verify and KeyCite reduce the risk, but lawyers must still check every citation and conclusion.
Can I use CoCounsel inside Microsoft Word or Claude?
Yes. The Drafting Agent in CoCounsel for Word works inside Microsoft Word, and since May 2026 a Model Context Protocol connection lets users reach CoCounsel Legal from Claude. A CoCounsel Legal experience inside ChatGPT Enterprise was in preview in September 2026.
This review is general information about a legal technology product and is not legal advice or a recommendation to buy. Features, availability and terms change often, so confirm details with Thomson Reuters and check your professional conduct obligations before using any AI tool on client work.
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