CoCounsel (Thomson Reuters)

What it actually does

CoCounsel is Thomson Reuters' AI assistant for legal work, built on GPT-4 technology that arrived with the $650 million Casetext acquisition completed in August 2023. It covers legal research, document review, contract drafting, risk assessment and case law analysis, and it runs against Westlaw and Practical Law rather than the open web.

That grounding is the point of the product. Ask a research question and the answer comes back with Thomson Reuters authority attached, which is why litigators will use it where they would not use a general chatbot. The skills map to real tasks: document review, timelines, tabular analysis, clause drafting and deposition prep, with Microsoft 365 integration so the work happens where lawyers already are.

What it costs

No public price and no self-serve trial. Everything runs through a Thomson Reuters quote, and in practice that quote rides on an existing Westlaw subscription, so the real cost is a Westlaw seat plus the add-on.

Any price figure you find online for this should be treated as unverified. We could not confirm one.

The other cost is procurement time. You need someone who can run a Thomson Reuters quote and contracting cycle, which rules out most solo practitioners before the software is even evaluated.

Note also that the product has been folded and rebranded into CoCounsel Legal. If you are reading reviews written in the Casetext era, you may be reading about a different product than the one you would buy.

Where it falls down

Accuracy. A preregistered study by Stanford researchers, published in the Journal of Empirical Legal Studies in 2025, found that leading retrieval-grounded legal research tools from Thomson Reuters and LexisNexis hallucinate more than 17% of the time, and the authors wrote plainly that "the providers' claims are overstated". That study tested Westlaw AI-Assisted Research and Ask Practical Law AI rather than CoCounsel by name, so the 17% figure is not a CoCounsel measurement and we will not present it as one. It is the same product family and the same marketing claims.

Lawyers report the failure mode in practice: fabricated or wrong content inside document summaries, delivered in a confident, authoritative tone. In legal work that is the worst possible way to be wrong, because the output reads like something you could file.

It is also a closed garden. Answers cite Westlaw and Thomson Reuters material only, so anything outside that corpus is invisible to you, and nothing in the output tells you a gap exists.

Practitioners describe what comes back as a ChatGPT-style overview of a legal question rather than a replacement for associate work, which makes the price hard to defend internally. One comparative legal evaluation scored it 37 out of 50, mid-pack rather than best in class, and some attorneys advise against it outright.

The review base deserves scrutiny too. G2 shows 4.7 out of 5 from 109 reviews, 88% five-star, with no one-star or two-star reviews at all. That distribution is unusually clean for an enterprise legal tool on a small sample. Thomson Reuters across all products sits at 4.2 from 844 reviews, and an independent expert review at Vaquill put CoCounsel at 3.9.

Who should buy it

Firms already paying for Westlaw, with enough document review and research volume that a percentage speed gain covers the add-on. The enterprise security posture and the Thomson Reuters name clear risk committees, which matters more in practice than it should, and the company reported 1 million users across 107 countries as of February 2026. Some firms report zero hallucinated cases in their own use.

Do not buy it if you are a solo or small firm without Westlaw, because the entry cost is the subscription rather than the AI. Do not buy it expecting to skip verification either. Check every citation it produces, every time, and if your workflow cannot absorb that checking step, the tool saves you nothing.

If what you actually need is a research overview rather than authority you can cite, a general assistant at $20 a month does a comparable job with the same verification burden and a fraction of the cost.