Lexis+ with Protégé vs Westlaw: how they compare in 2026

Lexis+ with Protégé is a generative layer over a research platform that is decades older and works without it. Without the models, Lexis+ remains a working research service, with Shepard's, case law, statutes and Practical Guidance intact; what goes is conversational search, drafting and summarization. LexisNexis says the AI was built internally with technology partners rather than acquired, and describes the retrieval platform as proprietary.

Westlaw works as a research service without its generative features. The base Westlaw Edge plan sells case law, statutes, regulations, KeyCite, the Key Number System, headnotes, Litigation Analytics and Quick Check with no generative AI, and Thomson Reuters still licenses it on its own. The models drive the two AI tiers. AI-Assisted Research answers plain language questions with links to authority, and Westlaw Advantage adds Deep Research, which plans and runs multistep research and returns a report, along with Litigation Document Analyzer, Complaint Analyzer, Claims Explorer, AI Jurisdictional Surveys and AI summaries of dockets. Thomson Reuters describes Deep Research as custom trained AI working with Westlaw's own research tools rather than a general chatbot placed over the content.

The product was marketed on legal citations free of hallucination, and quoted elsewhere as 100 percent free of hallucination; LexisNexis has not withdrawn the claim. It was tested in Magesh, Surani, Dahl, Suzgun, Manning and Ho, Hallucination-Free? Assessing the Reliability of Leading AI Legal Research Tools, 22 J. Empirical Legal Stud. 216 (2025), from Stanford RegLab and Stanford HAI, the first preregistered evaluation of commercial legal AI tools. It used 202 handbuilt queries across general research, jurisdiction and time specific, false premise and factual recall categories, scored by experts, with the dataset published. The product hallucinated on more than 17 percent of queries, was accurate on 65 percent, and gave incomplete answers on 18 percent, the best result among the systems tested. Grounding runs through a proprietary retrieval platform, sources reviewed by Shepard's editors, linked citations, a citation check tool and feedback in the product. LexisNexis disputed the figure, saying its internal data showed lower rates, and has not published that data. The study's first method drew objections from both vendors tested and was revised, access limits constrained the design, and the systems were tested in May 2024 and have changed since.

Deep Research runs an agentic process over Westlaw and Practical Law content with Westlaw's own research tools. It quotes primary law in the language of the source and links each authority to the full document. Its Verify tab lists cited and further relevant law to check the analysis, and AI Jurisdictional Surveys show KeyCite status beside each source. Litigation Document Analyzer reviews a whole brief for inaccurate citations, misstatements of law and hallucinated cases. Thomson Reuters says Deep Research can occasionally produce inaccuracies. In June 2024 it said internal testing showed AI-Assisted Research accurate about 90 percent of the time, without publishing the test set. The preregistered Stanford RegLab and HAI study (Magesh and others, Journal of Empirical Legal Studies, 2025) ran in May 2024. It found AI-Assisted Research accurate on 42 percent of 202 questions and hallucinating on about a third, nearly twice as often as the other legal tools tested. Thomson Reuters disputed the result, and Deep Research came after the test.

The RELX Responsible AI Principles name human oversight, and LexisNexis says human experts review model output for legal accuracy and that review and monitoring run across products. Citations are linked so a user can open the authority behind any point, a user can submit a citation to be checked and told when it may be wrong, and feedback in the product is said to improve accuracy. No autonomy threshold is set, nothing states what the system does without review, nothing describes what expert review covers or how often, and no escalation behavior is described. The independent study found incomplete answers on 18 percent of queries, so the system declines or under answers at a measurable rate, and LexisNexis documents no refusal behavior.

Each AI mode has a stated job and a stated stopping point. AI-Assisted Research answers a question the lawyer asks. Deep Research plans a multistep investigation and runs it without further prompts, shows its approach in step by step research notes, and returns a report with arguments on both sides and links to each authority. Its Enhance tab asks questions to tailor the report, and its Verify tab lists cited and further relevant law. The Deep Research help article sets a categorical limit. Its summary and list of authority should never be used to advise a client, write a brief or motion for a court, or otherwise be relied on without further research. The General Terms add that a licensed professional or similar expert must review AI output before anyone relies on it, uses it or passes it on. Nothing says what Thomson Reuters does once a wrong answer is reported.

The preview from May 2023 is described as covering global law firms, corporate legal departments, small law firms and US courts, and LexisNexis says preview feedback shaped specific changes before general availability in October 2023. The Stanford RegLab and HAI study found 65 percent accuracy across 202 expert scored queries, an outcome measured by a third party rather than claimed by the vendor. No customer, firm or court is named, no usage figure is published, and LexisNexis publishes no outcome measure of its own. The preview group is described only by segment.

Thomson Reuters says more than 50,000 law firms and legal departments use Westlaw, including 80 percent of the Am Law 100, along with more than 6,000 state government agencies and courts in 94 percent of states. The Department of Health and Human Services has granted Westlaw an Authority to Operate. A Thomson Reuters case study names Justly Prudent, a civil rights litigation firm, and credits CoCounsel and Westlaw AI with five times return on investment and a doubling of litigation capacity, without a method a reader can check. At the Deep Research launch in August 2025, Morgan Lewis's chief AI and knowledge officer was quoted on its reasoning, without figures. Usage of the AI tiers is not reported apart from Westlaw as a whole.

The LexisNexis General Terms, effective 5 June 2026, warrant that prompts and files submitted to the AI services will not be used to train any large language model and will be treated at least as confidential information. The confidentiality clause requires advance notice before any disclosure compelled by law, so the customer can seek a protective order. The annual SOC 2 Type 2 examination of Lexis and Lexis+ covers confidentiality and privacy as well as security. Legal professional privilege and attorney work product are not addressed by name, and no separation by matter is described. Document upload is a main feature, so client material enters the system by design.

Thomson Reuters' Legal AI Terms of 23 January 2026 govern AI features in its legal products. They bar Thomson Reuters and its third party providers from developing, training or fine tuning any generative or foundation model with user prompts, user content or outputs unless agreed separately in writing. The same terms let Thomson Reuters use prompts and outputs to evaluate safety and effectiveness, with automated safeguards meant to keep sensitive and identifying information out of the samples reviewed. The General Terms let a party disclose the other's confidential information under law, subpoena or court order only with prior notice where legally permitted. The Data Security Addendum keeps each customer's data logically segregated from other customers' data. Attorney client privilege and work product are not addressed by name, and nothing describes separation by matter within a firm.

Lexis+ with Protégé is governed by the LexisNexis General Terms, effective 5 June 2026, which say the online services are not legal, accounting, financial or other professional advice or a substitute for an attorney. The AI services clause adds that AI is not a substitute for independent professional advice and that users must verify what it provides. Nothing addresses a lawyer's own professional duties when relying on the output, and no jurisdiction or ethics guidance is named.

The General Terms say a licensed professional or similar expert must review AI output before anyone relies on it, uses it or passes it on. The customer alone is responsible for verifying its accuracy, and Thomson Reuters is not liable for decisions based on it. The Deep Research help article says its output should never be used to advise a client or write a brief or motion without further research. It presents the tool as a way to speed research rather than replace it. Westlaw is sold to law firms, legal departments, courts, government agencies and law schools, and the online plans are for law firms. Nothing addresses a lawyer's competence duties or names a jurisdiction's ethics rules.

The RELX Responsible AI Principles are named: transparency, fairness, human oversight and respect for privacy. LexisNexis says on a trust page that the product is built with them, that human experts review AI models for legal accuracy and ethical performance, and that continuous review and monitoring keep products accountable. No model card, bias or fairness testing method or result, evaluation output, accuracy monitoring figure, named governance body or review schedule is published, and there is no ISO 42001. The only published accuracy measurement comes from outside researchers.

Westlaw Edge, Precision and Advantage sit inside Thomson Reuters' ISO/IEC 42001:2023 certificate for its AI management system, issued by MSECB, held since March 2025 and valid to March 2028, and the certificate is published on the trust center. The Data and AI Governance and Security Program whitepaper of March 2025 makes the Responsible AI and Data Trust team responsible for AI governance and sends sensitive data uses to a Model Ethics Committee. Every business model must be registered in a central compliance hub and go through a data impact assessment that sets ethics controls such as human oversight and fairness, a model risk assessment, documented design and testing, monitoring and decommissioning. Attorney editors test and validate Westlaw's AI. No test results, bias findings or differences in performance across practice areas or jurisdictions are published.

LexisNexis publishes encryption, data minimization, pseudonymization, privacy built in at every stage of product development, secure cloud infrastructure, a set of information security policies, and incident response plans. Those plans are updated and tested periodically, with technical, administrative, business and executive escalation paths and outside firms on retainer. Retention follows where a document goes. Uploads of up to 10 documents outside a Vault are purged at the end of each session. A user can keep up to 50 encrypted Vaults of as many as 500 documents each until deleting them, and results from Vault work stay in the My Conversations history for 90 days. LexisNexis removes identifiable information from AI interactions and says data one user shares does not shape performance for other users. No retention period is stated for other prompts and research questions, no tenant separation is described, and no subprocessor list is available outside the trust center's registration step.

The Data Security Addendum, last modified 26 October 2026, encrypts customer data with 256 bit AES in transit and at rest. It limits access to authorized personnel with multifactor authentication, keeps each customer's data logically segregated, and commits to notice of a security breach within 72 hours. It offers a summary of penetration test results on written request and destroys customer data at the end of the service on request. The General Terms delete production data within 90 days after termination on written request, and the Data Processing Addendum dated 15 October 2026 deletes personal data on request. Thomson Reuters names the outside AI providers behind its generative features as Amazon Web Services, Anthropic, Google, Microsoft and OpenAI. No retention period is stated for prompts, uploaded documents or research history during a subscription, and the Westlaw data retention overview for Litigation Document Analyzer sits behind a Whistic account.

The LexisNexis General Terms and Conditions, effective 5 June 2026, govern its online services. LexisNexis defends and indemnifies the subscriber against third party patent, copyright, trademark and trade secret claims arising from use of the service, and that indemnity sits outside a twelve month liability cap. The AI Services clause says AI systems may not be accurate or error free, that users must verify information, and that AI is not a substitute for independent professional advice. No term covers a wrong answer or citation, though the product was earlier marketed on results free of hallucination.

Thomson Reuters' General Terms for the United States (version 6.0, 1 September 2026) cap each party's liability in a calendar year at the fees paid for the affected service over the prior twelve months. That cap doubles for breaches of confidentiality, data protection or security, and indirect and consequential loss is excluded. Thomson Reuters defends and indemnifies the customer against third party claims that use of the service infringes intellectual property, and that indemnity sits outside the cap. The service warranty promises conformity with the documentation, with repair, modification or replacement as the remedy. For AI output, the terms disclaim liability for its accuracy, legality or reliability and for decisions based on it.

The Lexis+ with Protégé product page says the product connects to iManage, SharePoint, NetDocuments and other document management systems so users can ask and draft from their organization's documents, alongside secure Vaults for uploaded files and shared Workrooms. Nothing describes what each connection syncs, in which direction, or what a firm must configure, and no API or developer documentation is published.

Westlaw's product and plan pages name no document management, practice management or Microsoft Word integration. The AI tools work on what a lawyer types or uploads: Litigation Document Analyzer, Complaint Analyzer and Quick Check take an uploaded brief or complaint. Deep Research also runs inside CoCounsel Legal, the separate Thomson Reuters assistant, which connects to iManage, NetDocuments and SharePoint. Thomson Reuters lists terms for a document management system integration among its legal products without saying what it moves or how a firm sets it up.

LexisNexis material refers to secure cloud infrastructure on enterprise platforms, naming no provider, region or residency commitment, and to strong encryption. No single tenant or dedicated option is described, and nothing says where customer queries or uploaded documents are processed and stored. The product is sold in the US, UK, Canada, Ireland and Australia under different data protection laws. The Canadian trust material raises PIPEDA and Quebec Law 25 as customer duties without stating LexisNexis's own residency position. The SafeBase trust center gives registered users further material.

Westlaw is a hosted service, and the Data Security Addendum keeps each customer's production data logically segregated from other customers' data. The Department of Health and Human Services has granted Westlaw an Authority to Operate, and Thomson Reuters says Westlaw is in the final stage of FedRAMP authorization. Separate security summaries cover the American, UK, Canadian, Australian and New Zealand editions. No hosting provider, region or residency commitment is published for the American service, and nothing separates where AI processing runs from where data is stored.

The trust center at trust.lexisnexis.com runs on SafeBase, with self serve registration through which authorized users reach compliance reports, a request flow that does not run through sales. Its May 2026 update announced SOC 2 Type 2, SOC 3 and HIPAA/HITECH reports for Lexis, Lexis+ with Protégé and CaseMap+, the SOC 2 Type 2 focused on security, availability and confidentiality and offered for secure download, and the SOC 3 open to read. An earlier LexisNexis description puts the annual SOC 2 Type 2 examination of Lexis and Lexis+ against all five Trust Services Principles. A SOC 1 Type 2 report for digital content management and IT services was updated in January 2026. The compliance list adds ISO/IEC 27001, ISO 22301, IRAP, NIST CSF, HIPAA and UK Cyber Essentials, certified on 26 October 2026 by Securious for LexisNexis UK's office and production AWS networks. The auditing firm for the SOC reports is not named. A March 2026 notice on the trust center reports that an unauthorized party reached a limited number of servers holding mostly legacy data from before 2020, such as customer names, user IDs, business contacts, survey responses and support tickets, and no client or matter information; LexisNexis engaged a forensic firm, reported the matter to law enforcement and informed affected customers.

The Westlaw security profile on Whistic, linked from the Thomson Reuters trust center, lists a Westlaw SOC 2 Type 2 report dated October 2025 and a bridge letter of November 2026, alongside a SIG Lite questionnaire, security summaries by country and an AI security FAQ. Downloading them needs a Whistic account under a Thomson Reuters confidentiality agreement, and the profile does not say the release is immediate. The ISO/IEC 42001:2023 certificate, which names Westlaw Edge, Precision and Advantage, is published openly. The Department of Health and Human Services has granted Westlaw an Authority to Operate, and FedRAMP authorization is in its final stage. The Data Security Addendum lets a customer review an executive summary of ISO 27001 or SOC 2 results on request. The SOC auditor and the report's scope are not stated publicly.

Protégé runs in two configurations. Protégé Legal AI blends several large language models from leading providers, which are not named, and grounds every response in LexisNexis sources with Shepard's citations. Protégé General AI gives access to models from OpenAI, Google and Anthropic, each with its own reasoning strengths and writing style, and LexisNexis says new configurations are assessed and added as they come. The retrieval platform is proprietary. Which models make up the legal configuration, which versions are offered, where the models run and which of them process customer uploads are not stated, and no notice of model changes is offered. No subprocessor list is published outside the trust center's registration step.

Thomson Reuters names the outside AI providers whose terms apply to its generative AI products: Amazon Web Services, Anthropic, Google, Microsoft and OpenAI. Deep Research is described as custom trained AI combined with Westlaw's research tools. Nothing maps a provider or model to AI-Assisted Research, Deep Research or the litigation tools, says where inference runs, or commits to notice before the providers change. Thomson Reuters announced its own legal model, Thomson, in August 2026 for CoCounsel Legal's tabular analysis, and nothing says it runs in Westlaw.

No price, range, tier or unit of charge is published for Lexis+ with Protégé, and nothing says whether it is licensed separately or bundled into a Lexis+ subscription. LexisNexis prices each organization by its size, the capabilities it needs and the content it licenses, and quotes on request through a form or by phone. A 2 day free trial is offered. Third party listings report about $128 to $494 per user per month, and LexisNexis has not confirmed them.

Thomson Reuters prices Westlaw online for new customers at law firms of up to 10 attorneys, by number of attorneys, jurisdiction and term. Westlaw Edge with AI-Assisted Research starts at $155.35 a month for single circuit coverage and $266.50 for all states and federal coverage, both on a three year term. Westlaw Advantage starts at $256.75 a month for single circuit coverage and $399.75 for all states and federal. Two year terms take 12 percent off and three year terms 18 percent, and plans include new features released during the initial term. Westlaw Edge without AI is sold online with no starting price stated. Firms with more than 10 attorneys and existing customers are quoted by sales, and documents outside a plan are charged at rates in Westlaw's subscriber pricing guide.

Grounding content is named as case law reviewed by Shepard's editors, statutes and Practical Guidance, described as the largest repository of legal content. The product is available in the US and in other LexisNexis markets, including the UK, Canada, Ireland and Australia. No jurisdiction or court list, date range, update lag or refresh frequency is listed, and nothing says which countries the AI features are available in, as distinct from where the platform is sold.

Westlaw serves law firms of every size, corporate legal departments, courts, prosecutors, public defenders, city attorneys, law enforcement, other government agencies and law schools. Thomson Reuters publishes practice area pages for business and commercial law, civil litigation, criminal defense, family law, labor and employment, mergers and acquisitions and personal injury. Content covers state and federal case law, statutes, regulations, court rules, administrative materials, dockets, briefs and secondary sources such as Wright & Miller and Corpus Juris Secundum. The plans set the limits. Westlaw Edge carries no generative AI, AI-Assisted Research and AI Jurisdictional Surveys come with Edge with AI-Assisted Research, and Deep Research, Litigation Document Analyzer, Complaint Analyzer and Claims Explorer come only with Advantage. A single circuit plan covers state and federal primary law for one circuit. Online buying stops at 10 attorneys, and separate editions serve the UK, Canada, Australia and New Zealand.