Lexis+ AI vs Westlaw Advantage Pricing and Accuracy

Lexis+ AI and Westlaw AI-Assisted Research are the two AI research products most US firms are choosing between, and neither name is current. LexisNexis replaced Lexis+ AI with Lexis+ with Protege on February 24, 2026, and Thomson Reuters replaced Westlaw Precision with Westlaw Advantage on August 13, 2025. The only independent measurement of the two, a Stanford RegLab study published in the Journal of Empirical Legal Studies, found Lexis+ AI accurate on 65% of test queries against 42% for Westlaw AI-Assisted Research, with hallucination rates of 17% and 33%. Thomson Reuters publishes a price. LexisNexis does not publish one for Protege.

That is the short version. The longer version matters because the two vendors have taken genuinely different bets, and the right answer depends on whether you are buying a research tool or a workflow platform. Here is what each one actually is, what the independent evidence says, what you will pay, and which one makes sense for a firm under ten attorneys.

What is Lexis+ AI now called?

Lexis+ with Protege. LexisNexis launched it on February 24, 2026 as a full replacement for Lexis+ AI rather than a rename, and expanded it again on May 7, 2026 with agentic skills, collaboration workrooms and customer-held encryption keys. The conversational research, document upload, summarization and drafting that Lexis+ AI did are all still there. What sits on top is a workflow layer that tries to carry a matter from research through to a draft.

The naming history is worth holding onto, because most of what ranks for these product names describes something LexisNexis no longer sells. Lexis.com became Lexis Advance, Lexis Advance became Lexis+ in July 2020, Lexis+ AI arrived in 2023, and Protege replaced it in 2026. We tracked those handovers in the guide to Lexis Advance vs Lexis+. One trap catches people constantly: the Lexis Advance name is still live in non-US markets, so a current-looking page about Lexis Advance pricing may be describing a product a US buyer cannot get.

What is Westlaw Advantage?

Westlaw Advantage is Thomson Reuters' current platform, announced August 5, 2025 and available from August 13, 2025. It follows WestlawNext in 2010, Westlaw Edge in 2018 and Westlaw Precision in 2022, and Thomson Reuters has called it the final named version on the theory that features will now ship continuously. Three things carry the release: Deep Research, which writes a research plan and executes it rather than summarizing a result list; Claims Explorer, which works from the facts of a matter toward candidate claims and defenses; and a Litigation Document Analyzer that reads an opposing brief and flags mischaracterized authority.

Two limits on Claims Explorer are easy to miss and matter a lot if you are not in a big state. It covers California, Florida, Georgia, Illinois, Massachusetts, New Jersey, New York, Pennsylvania and Texas. If you practice in Ohio or Louisiana, the headline feature of the release does not apply to your jurisdiction. The full version history is in our breakdown of Westlaw Precision and Westlaw Advantage.

Is Lexis+ AI or Westlaw AI more accurate?

On the only independent test that exists, Lexis was ahead by a wide margin. Varun Magesh, Faiz Surani, Matthew Dahl, Mirac Suzgun, Christopher D. Manning and Daniel E. Ho at Stanford RegLab ran the first preregistered empirical evaluation of these products, published as "Hallucination-Free? Assessing the Reliability of Leading AI Legal Research Tools" in the Journal of Empirical Legal Studies. Their finding, stated plainly in the abstract, is that the tools "each hallucinate between 17% and 33% of the time."

Read that table with two caveats, because without them it is misleading. First, the products tested were the 2024 versions. Both have since been replaced by the platforms described above, and neither vendor has submitted the current release to an equivalent independent test. The numbers describe what was measured, not what you would buy today. Second, "incomplete" is not the same failure as "hallucinated". Ask Practical Law AI scored badly mostly by declining to answer, which wastes your time but will not put a fake case in a brief.

What the study established beyond the specific percentages is more durable: retrieval-augmented generation reduces hallucination substantially compared to a general chatbot, and it does not eliminate it, despite vendor language about being hallucination-free. That is the finding to carry into a demo. We go through what the failure modes actually look like in can you trust AI for legal research and how to catch a bad cite before filing in avoiding AI hallucinated citations.

How much does each one cost?

Only one of them will tell you. Thomson Reuters publishes online pricing for Westlaw Advantage for firms of up to 10 attorneys, at $256.75 per month for single circuit coverage and $399.75 per month for all states plus federal, with 12% off a two-year term and 18% off a three-year term. Those online rates are available to new customers only; existing customers are routed to sales. Above ten attorneys there is no published price at all.

LexisNexis publishes rates only for its small-firm store, which sells to firms of one, two or three attorneys, and Lexis+ with Protege is not among them. On a three-year term the store lists Essential at $114 per attorney per month, Enhanced at $257, Professional at $324 and Deluxe Transactional at $217, with promotional rates limited to new customers. Protege itself is quoted as pricing on request. Two coverage gaps in that lineup are worth more than the headline numbers: Essential carries no federal case law at all, and Deluxe Transactional does not include Shepard's. The full breakdown sits in our guide to LexisNexis subscription pricing.

So the honest cost comparison is asymmetric. You can price Westlaw Advantage yourself in about a minute. You cannot price Lexis+ with Protege without a sales conversation, and that conversation will arrive attached to a multi-year agreement with an evergreen auto-renewal clause, typically requiring written notice some weeks or months before the term ends. If you are already in one of those, read how to switch legal research providers before you take a demo, because the notice window is usually the binding constraint rather than the price.

Which should a small firm buy?

Start by naming the job. If the job is research, you are paying an enterprise platform price for one of its modules. If the job is drafting, matter workflow and document analysis with research attached, the platform pricing starts to make sense, and Protege is the more committed version of that bet while Advantage is the more committed version of the research bet.

Three practical filters separate them faster than any feature grid:

• Jurisdiction. Check Claims Explorer coverage against where you actually practice before you value it at anything.
• Federal work. If you touch federal court, the cheapest Lexis store tier is disqualified outright, which changes the real entry price by well over a hundred dollars per attorney per month.
• Citator. Shepard's and KeyCite are the reason these platforms cost what they do, and a tier that drops the citator is not a cheaper version of the same product.

Neither tool touches the parts of a matter that sit outside the law library. In a shareholder dissolution you still need the operating agreement read closely, the discovery reviewed, and a defensible business valuation put in front of the court, and no research assistant is going to produce any of that. Buying a research platform to solve a workflow problem is how firms end up paying enterprise rates for software they use twice a week.

There is also a third option that most comparisons skip, because neither vendor is going to raise it. A large share of small-firm research is finding the controlling opinion, reading the holding, and confirming it has not been overturned. That work does not require a Westlaw or Lexis seat, and vLex Fastcase is free through more than 80 state, county and specialty bar associations, though it gives you citing lists without editorial treatment flags. We lay out the whole category, including the self-serve tier, in the guide to AI legal research tools and the wider comparison of legal research software.

Does Westlaw or Lexis have better AI for case law research?

On the independent evidence available, Lexis. On published pricing and on the specific question of agentic research depth, Westlaw Advantage has the stronger public case, and Deep Research is the more concrete description of what the software does with a question. Both vendors are shipping fast enough that a 2024 benchmark cannot settle 2026, which is exactly why the useful thing to do in a demo is bring your own five questions with known answers, ask for the citations, and check every one of them yourself.

That last step is not optional with either product. The Stanford result was not that one vendor is safe and the other is not. It was that both hallucinate, at rates far too high to file unchecked, and that the marketing on both sides overstates the case.

Casesearch is a research tool, not legal advice, and it is not yet on sale. Pricing of $39 Solo and $89 Firm is planned for launch and the waitlist is open. Competitor pricing above was verified from vendor pages in August 2026 and changes without notice.