Westlaw Precision AI and Lexis+ AI both let you ask a research question in plain English and get an answer with citations into their own case databases. That grounding is the real distinction from asking a general chatbot, which has no validated database behind it and no way to tell you whether a case is still good law.
The honest headline is that these two products are closer to each other than either is to the alternatives, and the right pick usually comes down to what you already pay for and how you research.
What each one actually does
Westlaw Precision AI sits on top of the Westlaw corpus, including headnotes, the Key Number System, and KeyCite. You ask a question, it returns a written answer with citations, and you can move from the answer into the underlying documents and their citing references. For a litigator, the value is that the answer is a doorway into the research system rather than a replacement for it.
Lexis+ AI covers the same ground on the Lexis corpus with Shepard’s for citation validation, and pushes harder on drafting. It will produce a first draft of a memo or a clause and connect the research to the document you are writing. If your workflow is research and then immediately draft, that integration removes a step.
Both also summarize documents you upload and answer questions about them.
The comparison that matters
| Westlaw Precision AI | Lexis+ AI | |
|---|---|---|
| Underlying corpus | Westlaw, with headnotes and Key Numbers | Lexis, with Shepard’s |
| Citation validation | KeyCite | Shepard’s |
| Research depth | Generally preferred by litigators | Very good, slightly less headnote-driven |
| Drafting integration | Present | More tightly integrated |
| Small firm pricing | Negotiable, often higher | Negotiable, often more flexible |
| Learning curve if you already use the platform | None | None |
The last row is doing more work than it looks. If your firm has used Westlaw for fifteen years, your muscle memory, your saved research, and your associates’ training are all on Westlaw. That switching cost usually decides this before any feature comparison does.
Where both still require you
Neither product removes the obligation to read what you cite.
The failure mode has shifted, which is worth understanding precisely. General chatbots invented cases outright, and that is what produced the early sanctions stories. Grounded research tools rarely do that. What they do instead is characterize a real case slightly wrong: stating a holding more broadly than the court did, missing that it was later limited, or citing a case that touches the issue without deciding it.
That error is harder to catch than a fabricated citation, because the case exists and looks right in the citation check. The only defense is reading the opinion.
Courts have not shown patience here, and the presence of a commercial legal vendor in the chain has not been treated as a defense. Your signature is on the filing. The analysis in AI ethics for lawyers covers where bar guidance has landed on supervision and competence.
What about CoCounsel
CoCounsel is Thomson Reuters’ broader legal AI assistant and overlaps with Precision AI while extending into document review, deposition preparation, and contract analysis. If you are already deep in the Thomson Reuters ecosystem it is worth evaluating alongside Precision AI rather than against Lexis, and the full review goes through where it fits.
How to buy this
Neither company posts real pricing, and both negotiate. That is not a complaint, it is a fact you should use.
Get a quote from both. Tell each that you are evaluating the other, because you are. Ask specifically what the AI features cost on top of your existing subscription, since they are often priced as an add-on rather than included, and firms are surprised by that at renewal.
Then run the same three real research questions from your actual practice through both trials. Not demo questions. Questions you have already researched, where you know the correct answer, so you can grade the output instead of being impressed by it.
Who should buy which
A litigation practice already on Westlaw should test Precision AI and will most likely stay. The research depth advantage is real and the switching cost is high.
A small firm or solo choosing fresh should get both quotes and expect Lexis to compete harder on price while bundling drafting.
A transactional practice that rarely needs case law should question whether either is worth it, and look at whether a general model plus a document-focused tool covers the actual need at a fraction of the cost.
Do this today
Write down the three research questions you have answered most recently where you already know the right answer. Book trials of both. Run those three questions through each and grade the citations by reading the cases.
That takes an afternoon and it will tell you more than any vendor demo, because the demo is built around questions the product answers well.