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Westlaw

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.