Why we built Thomson

There’s a moment every legal professional knows. You’re deep in a document review — hundreds of contracts, thousands of clauses, a deadline closing in — and you ask an AI tool a question that shouldn’t be complicated. The answer comes back confident, well-written, and subtly wrong. Not wrong enough to catch on first read. Just wrong enough to matter.

That’s why we built Thomson. Not just because general models get the details wrong sometimes, but because owning the model outright changes what we can do about it.

Thomson Reuters doesn’t just deploy AI. We build it.

Why general-purpose AI isn’t enough

The past few years have brought extraordinary AI advances. General-purpose large language models (LLM) can write code, summarize articles, and hold nuanced conversations. But legal and compliance professionals work in a different environment. Imprecision has consequences. A misread clause or a missed precedent isn’t an inconvenience; it’s a risk you can’t take.

So what separates a tool that’s merely useful from one you can stand behind?

Not all AI is built for the same stakes. At one end are general-purpose tools — broadly useful, but shallow on any one domain. A step further are professional-grade tools, built for a specific field, in environments where an occasional error is tolerable. And then there’s a third tier: Fiduciary-Grade AI™, built for work where a small error doesn’t just cost time, it can mean a lost case or a client’s trust.

That’s the tier legal and compliance work lives in. It’s the tier Thomson was built for.

The decision to build our own

We’ve always been an expertise company. Grounded by 175 years of intelligence, we’ve combined proprietary data with domain knowledge to give professionals the intelligence they need for their most important work. Thomson is the next chapter of that mission.

Owning more of the AI stack gives us greater control over performance, economics, deployment, and sovereignty — how the model behaves, what it costs us to run, where it runs, and how our clients’ data is protected. Just as importantly, it lets us continuously improve Thomson using the content and expertise only Thomson Reuters has, rather than depending on what a third party chooses to build next.

That decision started in 2024, when we acquired Safe Sign Technologies, an AI research company founded by leading AI and legal minds. The result is a model that’s built on open-source foundations we can evolve as the AI landscape shifts, while the legal intelligence we put into Thomson only deepens over time. We’re not locked into any single foundational system — and we’re not standing still.

What we built

Thomson is our proprietary LLM, purpose-built by Thomson Reuters for high-stakes professional work. It was built on our proprietary content, including Westlaw and Practical Law, two of the most authoritative legal data sources in the world, and reflects input from our vast network of human legal experts.

Think of it as a “T-shaped” model. The horizontal bar is broad general capability — language understanding, reasoning, and the fundamentals any strong AI needs. The vertical column is what makes Thomson different: authoritative legal content and deep subject-matter expertise, refined by expert guidance, producing a level of legal comprehension optimized specifically for professional work. We built it to be both broad and deep.

Thomson and CoCounsel aren’t the same thing, and that’s by design. CoCounsel is the product — the agentic workspace, skills, and workflows legal professionals use every day. Thomson is one of the LLMs CoCounsel calls on.

What it’s already doing

Thomson’s first implementation just launched, powering CoCounsel Legal’s Tabular Analysis feature. You can extract structured answers from up to 10,000 documents across up to 100 questions you define — at a scale and consistency that used to be impossible without significant time and cost.

Powering the engine behind Tabular Analysis, Thomson gives you deeper comprehension of complex legal documents, more consistent extraction across question types, lower variance across large document sets, and verifiable, citation-grounded outputs your attorneys can review and rely on. These aren’t incremental improvements — the numbers show it. As of Q1 2026, CoCounsel has crossed one million users. The share of our business that’s Gen AI-enabled has doubled in a little over a year. Monthly CoCounsel SKUs in legal have quadrupled year-over-year. That’s not a pilot program. That’s a shift in how the work gets done.

Independent testers agree. A Washington University law professor pitted Thomson against ChatGPT and Claude using real questions from his own Corporate Tax class and preferred Thomson’s answers overall, pointing to its linked citations to treatises as especially useful. A separate review from Queen’s Conflict Analytics Lab and Cornell Legal AI Lab found Thomson’s citation quality held up against leading frontier models — even on Canadian employment-law questions the model wasn’t specifically tuned for.

We hold Thomson to the same standards you hold your own work to. It’s developed and deployed within enterprise-grade governance frameworks grounded in the principles of Fiduciary-Grade AI™: transparency, traceability, verifiability, structured evaluation, and expert validation. Thomson is built for repeatable performance you can trust.

Built for the people who make change real

Speed is the easy part. Any AI tool can give you an answer fast. What you need is one you can stand behind — in front of a judge, a client, a board. That’s what we mean by Fiduciary-Grade AI™: intelligence built to the standard your profession already holds itself to.

The legal professionals who rely on us every day aren’t passive consumers of information.

You’re the people who protect businesses from harm, hold institutions accountable, and shape the frameworks that govern how society works. You’re changemakers — and you deserve tools built with the same seriousness you bring to your work. Changemakers don’t just need answers. You need answers you can defend.

You’re in good company: a million professionals like you have already chosen to trust Thomson Reuters with the work that can’t afford to be wrong.

We built Thomson for you. Not because AI is a trend worth chasing, but because the next phase of professional AI won’t be defined by general capability — it’ll be defined by domain mastery, measurable outcomes, and trust. That means higher-quality outputs and greater confidence when you’re using AI in the workflows that matter most.

You shouldn’t have to settle for AI built for everyone. Now you don’t.

Thomson

The purpose-built, proprietary LLM, engineered for high stakes professional work

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