Thomson Reuters Brings HighQ and CoCounsel Legal to ChatGPT Enterprise

Thomson Reuters is bringing its legal AI tools into ChatGPT Enterprise. The company announced on 17 September 2026 that HighQ, its matter and collaboration platform, is now available inside ChatGPT Enterprise through a Model Context Protocol (MCP) connection. It is also previewing a CoCounsel Legal experience that will let lawyers reach CoCounsel’s capabilities directly from ChatGPT. The full CoCounsel experience has not launched yet. Thomson Reuters describes it as coming.

The OpenAI tie-up is the third of its kind in four months. Thomson Reuters connected Claude to CoCounsel Legal with Anthropic in May, and linked HighQ to Google Cloud’s Gemini Enterprise for Legal in August. Now it has done the same with OpenAI. The pattern is deliberate. Thomson Reuters is betting that lawyers will do their work in whichever AI assistant their firm has chosen, and that its value lies in the content and matter data those assistants need to reach.

What was announced

The announcement came in a post by Joel Hron, Thomson Reuters’ chief technology officer. It has two parts.

HighQ in ChatGPT Enterprise, available now. HighQ is where many firms keep matter documents, deal rooms and client collaboration. Through the MCP connection, a lawyer working in ChatGPT Enterprise can draw on the matter context they are already authorised to see in HighQ. Hron frames the condition plainly: “Open cannot mean uncontrolled.” Security, permissions, governance and audit are meant to stay attached to the work when it moves into ChatGPT.

CoCounsel Legal in ChatGPT Enterprise, in preview. Thomson Reuters is previewing an experience that will let lawyers use CoCounsel Legal capabilities from inside ChatGPT, alongside their HighQ matter context. The company has not given a date for general availability.

In a statement to Legal Desire, Hron said:

Joel Hron, Chief Technology Officer, Thomson Reuters

“Legal professionals shouldn’t have to choose between the flexibility of the AI tools they want to use and the trusted intelligence they need to do high-stakes work. Our work with OpenAI is about bringing those two worlds together. By connecting environments like ChatGPT with the matter context in HighQ and the specialized legal capabilities of CoCounsel Legal, we can give professionals greater choice in where they work while ensuring security, governance, and accountability travel with them. That kind of interoperability is where we believe legal AI is headed: not one model or interface, but an open ecosystem built around the intelligence that best fits the task.”

How it fits with OpenAI’s move into legal

The timing matters. On the same day, OpenAI released Astra for Law, a version of its GPT-6 Astra model configured for legal work, with a dedicated legal search index. LawSites reported that OpenAI is offering it to API customers, including Harvey and Legora, and to Am Law 200 firms through a “Trusted Access” programme. According to the same report, Thomson Reuters is one of 26 vendor partners building plugins for ChatGPT. Its plugin brings HighQ matter context in first and adds a connector to CoCounsel Legal later.

For firms, the effect is that ChatGPT Enterprise is becoming a place where legal content providers plug in, rather than a general assistant used alongside them.

One strategy, three AI platforms

The Gemini connection is the best guide to how the ChatGPT one is likely to behave. For Gemini, Thomson Reuters said users sign in with their HighQ credentials. It said matter walls, folder permissions, document-level security and audit logging all stay in force, and that the connection is read-only, so the AI cannot change the underlying documents. Thomson Reuters has not published the same level of detail for the ChatGPT connection. Firms should confirm those points directly before switching it on.

CoCounsel Legal itself was rebuilt this summer. The next-generation version, launched in the United States on 20 August 2026, is built on Anthropic’s Claude Agent SDK and grounded in Westlaw and Practical Law. Thomson Reuters says CoCounsel products are used by one million professionals across 107 countries, and it expects to launch in Canada, the UK and Australia later in 2026.

What it means for firms and legal teams

The front end is becoming a choice. Firms have been told for two years to pick an AI platform. Thomson Reuters is now telling them the platform matters less than the content and matter data behind it. A firm standardised on ChatGPT Enterprise, Gemini or Claude can reach HighQ from any of them.

Governance becomes the key question. Moving matter documents into a general assistant raises obvious risks: ethical walls, client confidentiality and records of who saw what. The promise is that HighQ’s permissions travel with the data. Before switching the connection on, a firm should check four things:

• whether HighQ’s permissions and matter walls apply inside ChatGPT exactly as they do in HighQ
• whether the connection is read-only
• where the audit log sits
• how its OpenAI Enterprise agreement treats client data

For firms in Europe, the EU AI Act’s transparency duties have applied since 2 August 2026, and they reach AI used in client-facing work. Our guide to what applies after the Digital Omnibus explains where those duties bite.

Frequently asked questions

What did Thomson Reuters and OpenAI announce?

On 17 September 2026 Thomson Reuters made HighQ available inside ChatGPT Enterprise through a Model Context Protocol connection. It also began previewing a CoCounsel Legal experience that will let lawyers use CoCounsel capabilities from ChatGPT.

Is CoCounsel Legal available in ChatGPT now?

Not yet. Thomson Reuters describes the CoCounsel Legal experience in ChatGPT Enterprise as a preview of something coming, and has not given a launch date. The HighQ connection is live.

Which AI assistants does Thomson Reuters now connect to?

Claude through CoCounsel Legal (announced May 2026), Gemini Enterprise for Legal through HighQ (August 2026), and ChatGPT Enterprise through HighQ, with CoCounsel Legal in preview (September 2026).

What is MCP?

Model Context Protocol is an open standard that lets AI assistants connect to outside systems and data sources, such as a document platform, through a defined interface rather than a custom integration for each assistant.

What is Astra for Law?

A version of OpenAI’s GPT-6 Astra model configured for legal work, released on 17 September 2026, with a dedicated legal search index. It is aimed at legal technology companies and large law firms.