Three Years After Launching As First AI Legal Assistant, CoCounsel Reaches 1 Million Users — and Thomson Reuters Teases What’s Ahead

Above the Law

by Robert Ambrogi

February 26, 2026

AI-Generated Deep Dive Summary

CoCounsel, an AI-powered legal assistant developed by Casetext, has reached a significant milestone: one million users across 107 countries just three years after its launch on March 1, 2023. Acquired by Thomson Reuters (TR) for $650 million shortly after its release, CoCounsel has become an integral part of TR’s product portfolio, integrating into key platforms like Westlaw and Practical Law. This achievement marks a broader shift in the legal profession, moving from experimental AI use to embedding it as core infrastructure. According to TR’s CEO Steve Hasker, professionals are no longer debating whether to adopt AI but are instead choosing which systems they trust with critical tasks. CoCounsel’s success stems from its tailored design for professional environments where outputs must meet rigorous standards—such as courtroom scrutiny or regulatory reviews. Built on GPT-4 and enhanced with inputs from TR’s extensive library of legal, tax, and compliance content, CoCounsel provides structured, citation-backed results rather than generic text generation. This approach ensures reliability and accuracy while maintaining trust in sensitive workflows. TR has also emphasized strict data privacy standards, ensuring that customer inputs are not used to train third-party models or shared with other users. The journey to reaching one million users involved refining CoCounsel’s AI capabilities based on real feedback. Initially prioritizing accuracy over fluidity, the system evolved into a more balanced tool capable of being both reliable and genuinely helpful. This evolution led to advancements like Westlaw Deep Research, an advanced AI-powered legal research system that synthesizes findings across jurisdictions and delivers court-ready analysis with citations. Looking ahead, TR is teasing the next generation of CoCounsel Legal, set to enter beta soon. This update promises further enhancements in AI capabilities, continuing the trend of embedding intelligent systems into professional workflows. For legal professionals, this represents a significant leap forward in efficiency and accuracy, highlighting how AI is transforming traditional practices while maintaining the

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Originally published on Above the Law on 2/26/2026