CoCounsel

CoCounsel began as Casetext's AI legal assistant, launched March 1, 2023 on early access to GPT-4 (Thomson Reuters Institute, thomsonreuters.com/en-us/posts/innovation/from-capability-to-confidence-how-cocounsel-is-redefining-legal-ai). Thomson Reuters acquired Casetext for $650 million cash, announced June 26, 2023 and closed August 17, 2023 (Thomson Reuters press release, thomsonreuters.com/en/press-releases/2023/august/thomson-reuters-completes-acquisition-of-casetext-inc). The standalone Casetext product was retired April 1, 2025; existing Casetext subscribers were migrated onto Thomson Reuters plans (Thomson Reuters CoCounsel 2.0 migration guide, thomsonreuters.com/en-us/help/cocounsel/legal/get-started/cocounsel-2-0-migration-information). On August 20, 2026 Thomson Reuters shipped a rebuilt, fully agentic version of CoCounsel Legal, built on Anthropic's Claude Agent SDK, with general availability in the US and expansion to Canada, the UK and Australia "expected later this year" (Thomson Reuters press release, thomsonreuters.com/en/press-releases/2026/august/thomson-reuters-launches-next-generation-of-cocounsel-legal-the-ai-ecosystem-built-for-legal-professionals). Thomson Reuters says one million professionals across 107 countries now use CoCounsel across its legal, tax and audit product lines — a vendor figure, not independently verified, and it spans the whole CoCounsel family, not just the legal product (same source; also thomsonreuters.com/en/press-releases/2026/february/one-million-professionals-turn-to-cocounsel-as-thomson-reuters-scales-ai-for-regulated-industries).

Vals AI's Vals Legal AI Report (VLAIR), published February 27, 2025, is the first independent benchmark of legal AI tools using real Am Law 100 work, tested against a practicing-lawyer control group across four tasks: document Q&A, chronology generation, document summarization, and data extraction (vals.ai/application-reports/cocounsel; vals.ai/industry-reports/vlair-2-27-25). CoCounsel scored the highest average across the four tasks at 79.5%, topped the field on document summarization (77.2% vs. a 50.3% lawyer baseline), and beat the lawyer baseline on three of four tasks, though it slightly underperformed the baseline on chronology generation (78.0% vs. 80.2%). This is the strongest third-party evidence in the legal-AI category that CoCounsel's outputs hold up against a lawyer doing the same work, not just against other AI tools. It predates the August 2026 agentic rebuild, so it speaks to the underlying model/retrieval quality rather than the newest workflow features.

Thomson Reuters publishes a self-serve configurator for firms up to 10 attorneys at sales.legalsolutions.thomsonreuters.com/en-us/products/cocounsel-legal/700/plans-pricing; above that, pricing is quote-only. There are three purchasable bundles plus a pay-per-task option: CoCounsel Essentials (the AI assistant alone, no Westlaw or Practical Law content), Westlaw Advantage with CoCounsel Essentials, Practical Law Dynamic Tool Set with CoCounsel Essentials, and CoCounsel Legal (the full bundle including Westlaw Advantage, Practical Law Dynamic Tool Set, and Deep Research). A third-party breakdown using the live configurator (5 attorneys, all-states-and-federal jurisdiction, 1-year term, checked September 3, 2026) puts CoCounsel Essentials at roughly $1,464/month and full CoCounsel Legal at roughly $2,462/month for five seats — about $293 and $492 per seat respectively (Spellbook, spellbook.com/learn/cocounsel-pricing). We could not independently reproduce these exact figures — the configurator is client-rendered and requires a jurisdiction/seat-count selection we did not complete — so treat them as directionally right rather than exact. Multi-year contracts reportedly carry a roughly 12% discount at 2 years and 18% at 3 years, per the same source citing the configurator. The entry-level Essentials tier, without Westlaw or Practical Law, lacks primary-law search and KeyCite citation validation — the features most reviewers cite as CoCounsel's real value.

CoCounsel's core pitch is that its outputs are grounded in Westlaw primary law and Practical Law secondary sources rather than general web data, with a dual-layer citation system (synthesized text plus exact source quotes in footnotes) that the VLAIR evaluators called out as distinctive (vals.ai/application-reports/cocounsel). That grounding is real leverage for firms that already carry Westlaw and Practical Law subscriptions, where the bundle price undercuts buying the pieces separately. For firms that don't already subscribe to Westlaw — particularly contract-focused practices without a research-heavy workload — the full value of CoCounsel requires paying for research content that a Westlaw-independent tool wouldn't require, which several reviewers flag as the main friction point (Lawyerist review, lawyerist.com/reviews/artificial-intelligence-in-law-firms/cocounsel-review-artificial-intelligence-for-lawyers, notes "Expensive," "Add-on Product" among its cons and rates Price & Value separately from its 4.6/5 overall score).

CoCounsel Legal is SOC 2 and ISO 42001 certified, per its own product page (legal.thomsonreuters.com/en/products/cocounsel-legal/corp). Thomson Reuters states it does not use customer content or prompts to train CoCounsel or any third-party LLM (thomsonreuters.com/en/cocounsel, FAQ section repeated across regional Thomson Reuters product pages). These are vendor disclosures we could confirm are published, not independently audited claims we verified against a report.

G2 lists CoCounsel Legal at 4.8/5 across 326 reviews as of this check (g2.com/sellers/thomson-reuters/solutions/cocounsel-legal, via search result; direct fetch was blocked by G2's bot protection so this figure comes from a search snippet, not a page we read in full). Lawyerist, a legal-industry review site, rates it 4.6/5 overall, praising its contract review, document analysis, and legal-market focus, while listing "Expensive," "Add-on Product," and "Not for Caselaw Research" as cons and noting pricing requires contacting Thomson Reuters (lawyerist.com/reviews/artificial-intelligence-in-law-firms/cocounsel-review-artificial-intelligence-for-lawyers).