Legal AI
Westlaw AI-Assisted Research
High riskGenerative AI research feature inside Westlaw Precision that answers legal questions in prose with citations drawn from the Westlaw database.
Is Westlaw AI-Assisted Research safe for confidential data?
The data handling is enterprise-grade (same Thomson Reuters stack as CoCounsel: no training on customer content, SOC 2 and ISO 27001, DPA available), so the high rating is about output reliability, which for a research tool is the product. The peer-reviewed Stanford RegLab study (Journal of Empirical Legal Studies, 2025) found Westlaw's AI-Assisted Research hallucinated on roughly a third of tested queries — about twice the rate of Lexis+ AI — while producing complete, accurate answers only around 42% of the time, despite Thomson Reuters marketing that leaned on hallucination-avoidance. Because answers arrive in confident prose with real-looking citations inside the platform lawyers trust most, unverified reliance is the specific, documented failure mode: Damien Charlotin's database of court decisions involving AI-hallucinated material passed 1,600 cases in mid-2026. Use it as a drafting accelerant, never as authority.
Risk by plan
The same product often carries very different terms depending on the tier — consumer plans are where the exposure concentrates.
Available only as part of a Westlaw Precision subscription under Thomson Reuters' standard enterprise terms; no consumer tier.
Data handling
Training on inputs
Thomson Reuters states customer queries and content are not used to train its models or third-party LLMs; LLM providers are contractually barred from training on customer data.
Retention
Third-party LLM calls follow Thomson Reuters' zero-retention pattern; research history is retained in the customer's Westlaw account under subscription terms.
Residency
Processing is U.S.-based; non-U.S. firms should confirm cross-border transfer terms in the Thomson Reuters DPA.
Compliance
- SOC 2Yes
- GDPR / DPAYes
- HIPAA BAANot verified
Certifications typically apply to specific tiers and contracts — confirm scope in writing before relying on them.
New to these frameworks? See our plain-language guides to SOC 2 and the other AI compliance standards.
Enterprise controls
- SSO / SAML
- Contractual no-training terms with LLM providers
- SOC 2 Type II and ISO 27001 certifications
- Standard Thomson Reuters DPA available
Frequently asked questions
Does Westlaw AI-Assisted Research hallucinate?
Yes, at a documented rate. The Stanford RegLab study, peer-reviewed and published in the Journal of Empirical Legal Studies in 2025, measured hallucinations on roughly 33% of queries — about double the rate of Lexis+ AI in the same test — and found complete, accurate answers only about 42% of the time. Thomson Reuters disputed aspects of the study's methodology, but no vendor has published contrary independent benchmarks.
Is Westlaw AI-Assisted Research reliable enough for filings?
Only as a starting point. Every proposition and citation needs independent verification in the underlying sources before it reaches a filing — ABA Formal Opinion 512 makes clear the lawyer remains responsible for AI-assisted work product, and courts have sanctioned lawyers in a growing body of cases tracked in Charlotin's public database. The tool's citations link to real Westlaw documents, which makes verification fast; skipping it is the documented route to sanctions.
Our associates already use ChatGPT for research — is Westlaw AI at least safer than that?
For confidentiality, considerably: queries stay under an enterprise agreement with no-training terms, instead of a consumer chatbot's defaults. For accuracy, the gap is smaller than the price difference implies, which is why the sensible posture is both a sanctioned, grounded research tool and firm-level controls over what gets pasted into consumer AI — one does not substitute for the other.
Policy changelog
- Initial entry published from Thomson Reuters' published security documentation and cited independent research.
Sources
- Stanford RegLab: Hallucination-Free? Assessing the Reliability of Leading AI Legal Research Tools
- Published study (Journal of Empirical Legal Studies, 2025)
- AI Hallucination Cases database (Damien Charlotin)
- Thomson Reuters Data Processing Addendum
This profile summarizes the vendor's published policies as of the verification date. It is not legal advice.
Westlaw AI-Assisted Research is probably already in your organization.
Sanitized AI shows you who is using it and redacts sensitive data from prompts before it leaves your control.
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