CoCounsel Legal vs Westlaw: how they compare in 2026

CoCounsel Legal exists only as a generative and agentic layer, rebuilt in 2026 on an agent framework so it plans, reasons and executes multi step legal work. Without the models there is no product, only the underlying Westlaw and Practical Law content, which the parent sells separately as its own products.

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 research agent identifies key legal concepts, selects Westlaw tools including KeyCite, the Key Number System and annotated statutes, runs multiple search cycles and synthesizes a structured result. Output grounds to primary authority the user can open, with inline citations, a Sources tab with direct links and highlighted excerpts, and KeyCite validity flags shown with the authority. A citation level verification feature, Deep Research Verify, is published, and prompting guardrails restrict output to content validated by people rather than the open internet. CoCounsel took part in the February 2025 Vals Legal AI Report, a third party benchmark against a measured lawyer baseline, scoring between 73.2 and 89.6 percent across four tasks with a 79.5 percent average, each task more than 10 points above the lawyer baseline. Thomson Reuters also publishes CoCounsel Bench, under which attorneys reviewed 50 complex tasks of about six lawyer hours each and judged the product's response stronger than the expert reference answer on nearly 40 percent. The 2025 study measured task accuracy rather than citation validity or hallucination rate, and Thomson Reuters did not take part in the later Vals study on citation authoritativeness.

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.

Thomson Reuters states that its AI is built with human oversight at its core and publishes a Fiduciary-Grade AI framework built around transparency and accountability. The product is described as showing its plan before executing: it interprets a request, builds a plan specific to the matter, and returns work product with traceable citations the user can open and check. No threshold is published at which an agent stops and returns to a lawyer. The General Terms require a licensed professional or similar expert to review AI output before anyone relies on it, and nothing says what Thomson Reuters does once a wrong answer is reported. The August 2026 release moved the product from structured skills to a fully agentic experience.

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 publishes case studies naming Justly Prudent, reporting five times return on investment and a doubling of litigation capacity, and Brinks, on reducing outside counsel spend. It also publishes a commissioned Forrester Total Economic Impact study dated 2026, with its method set out and its commissioned status disclosed on the page. Aggregate figures are published with the population stated, including 2,700 corporate customers using the CoCounsel family and a 61 percent reduction in time to draft correspondence.

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, part of the customer agreement, bar Thomson Reuters and its third party providers from training or fine tuning any generative or foundation model on prompts, user content or outputs unless agreed separately in writing. Prompts and outputs may be used to evaluate safety and effectiveness, with automated safeguards that keep sensitive and identifying information out of those samples. A published FAQ states plainly that customer content and prompts are not used to train or improve the product or the underlying models. Third party model partners, including OpenAI and Google, are contractually prohibited from training on customer data, and systemic controls turn off those parties' abuse monitoring so there is no human access to customer data. Thomson Reuters also publishes a zero retention API architecture and data residency controls. The General Terms treat customer data as confidential information and allow its disclosure under law, subpoena or court order only with prior notice where legally permitted. Attorney client privilege and work product handling are not addressed directly. Thomson Reuters does not describe segregation by matter, although the product is built around matters.

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 product is sold to licensed professionals and distributed to more than 200 law schools and 120,000 law students. Thomson Reuters frames the system as working at the level of a senior associate under professional supervision, and its General Terms for the United States put that supervision into the contract: a licensed professional or similar expert must review AI output before anyone relies on it, uses it or passes it on, and the customer alone is responsible for verifying it. The same terms say the service is provided for information and not as legal advice. The product page, the AI hub, the trust center, the legal blog and the terms name no jurisdiction limits and say nothing of a lawyer's competence duties.

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.

Thomson Reuters publishes a named standard it calls Fiduciary-Grade AI with a buying framework attached, describes a dedicated research organization of more than 1,000 specialists, states a figure for annual responsible AI investment, and answers a direct published question on bias: prompting guardrails restrict output to a clearly defined and limited set of human validated content rather than the open internet. No named internal owner of model governance, pre release testing results, or disclosure of uneven output across matter types, parties or populations is published. The bias answer describes a content restriction rather than testing for disparate output.

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.

SOC 2 Type II and ISO 27001 are maintained and ISO 42001 certification is referenced for the AI management system. Thomson Reuters publishes a zero retention API architecture, data residency controls, 24 hour security monitoring and threat detection, corporate identity management integration, and a corporate trust center carrying the information security framework. The Data Security Addendum that the General Terms apply, last modified 26 October 2026, commits to notice of a security breach within 72 hours, and the General Terms delete production data within 90 days after termination on written request. No current named subprocessor list is published for this product. The two named model partners are disclosed in the AI FAQ rather than in a maintained subprocessor list.

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.

CoCounsel Legal is sold under Thomson Reuters' General Terms for the United States (version 6.0, 1 September 2026), which cap each party's liability in a calendar year at the fees payable for the affected service in the twelve months before the claim. The 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, except for claims arising from third party services Thomson Reuters licenses, which are capped at twice the prior twelve months' fees. The service warranty promises conformity with the documentation, with repair, modification or replacement as the remedy and termination if that fails. For AI output, the terms disclaim liability for its accuracy, legality or reliability and for decisions based on it, and the customer must have a licensed professional or similar expert review it before relying on it. The Legal AI Terms of 23 January 2026, which govern the AI features, add no liability term of their own, and neither document states an insurance position.

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.

Named connections span document management with iManage, NetDocuments and SharePoint, Microsoft 365, the parent's own HighQ collaboration platform and Legal Tracker, contract lifecycle through Icertis, plus DeepJudge, Supio and Smokeball, and a Word add in carrying a personal clause library. An MCP integration lets a lawyer reach the product from a separate AI client without switching platforms. No documentation describes what each integration moves, in which direction, or what an administrator must configure.

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.

Published data residency controls keep information within required geographic boundaries. The rollout is sequenced by country across the United States, Canada, the United Kingdom and Australia, and FedRAMP In Process status is held for the underlying Westlaw and Practical Law products, with stated investment toward authorization for this one. The list of available regions, the tenancy model, what changes between tiers, and where processing happens as distinct from where data is stored are not published.

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.

SOC 2 Type II and ISO 27001 are stated as maintained, and ISO 42001 is referenced for the AI management system. FedRAMP In Process status is published for Westlaw and Practical Law, with authorization stated as an investment goal for this product, and a corporate trust center publishes the information security management framework. No attestation report, coverage period, audit scope or named auditor is published, and no route to request the reports without a sales conversation is published either. Certifications are stated at the parent company level rather than scoped to this product.

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.

Anthropic's Claude Agent SDK is named as the architecture of the current release, and a published FAQ names OpenAI and Google as third party AI partners and states the contractual position imposed on them. Which model serves which task, where the models run, a maintained subprocessor list for this product, and any commitment to notify customers before the model supply chain changes are not published.

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.

Tier names and feature splits are published and reachable from the main navigation: CoCounsel Essentials, Westlaw Advantage with CoCounsel Essentials, Practical Law Dynamic Tool Set with CoCounsel Essentials, and CoCounsel Legal. Each has its own plans and pricing page, with variants for law firms, corporations and government. An online configurator on the Thomson Reuters sales site prices new customers at law firms of up to ten attorneys by number of attorneys, jurisdiction and plan length. For one attorney it shows CoCounsel Essentials at $360.00 a month on a one year plan and $292.50 a month on a three year plan, with 12% off for two years and 18% off for three. Firms with more than ten attorneys and existing customers are routed to a sales quote, so no figure is published for the larger part of the range.

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.

Published navigation separates law firms under ten attorneys from firms over ten, and separately addresses corporations, government (including courts, prosecutors, public defenders, city attorneys and law enforcement), and academic use across more than 200 law schools. Practice areas are listed with their own pages, spanning business and commercial, civil litigation, criminal defense, family, labor and employment, mergers and acquisitions and personal injury. The published table of plans shows which content each plan reaches.

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.