Microsoft 365 Copilot adds two third-party AI models from 30 September 2026: each needs a subprocessor switched on, and usage limits apply

Microsoft 365 Copilot adds two third-party AI models from 30 September 2026: each needs a subprocessor switched on, and usage limits apply

1 October 2026: Microsoft is adding two more outside AI models to Microsoft 365 Copilot: OpenAI's GPT-6.1 Sol and Anthropic's Claude Sonnet 5.5. According to a Message Center post published on 30 September 2026 and updated on 1 October (MC1483844), they begin rolling out with usage-based billing in Cowork and Copilot Studio from 30 September, and in phases across Word, Excel, PowerPoint and Chat "in the coming week" for users with a Microsoft 365 Copilot user subscription licence.

Not yet independently verified. This rests only on Microsoft’s own Message Center post, read through a public archive because the admin centre requires sign-in. Microsoft does not publish the usage limits. No independent report was found. We will update this when it can be confirmed, and remove this note.

The part that needs a decision: subprocessors

Using these models means data leaves Microsoft for another company's systems. Microsoft's post says:

• "Access to Claude Sonnet 5.5 additionally requires the Anthropic subprocessor to be enabled in your organization."
• "Access to GPT-6.1 Sol additionally requires the OpenAI subprocessor to be enabled in your organization for select surfaces."

So whether users can pick these models depends on settings that an administrator controls. Whoever owns your data-protection position, not only IT, should make that call: switching a subprocessor on adds a processor of your users' prompts and documents.

Limits and billing

• In Cowork and Copilot Studio the models are billed by usage, for users whose licence has usage-based billing enabled.
• In Word, Excel, PowerPoint and Chat they come with the Copilot licence, subject to limits. Microsoft says the limits are designed so that "the vast majority of users are not expected to reach them", and that users nearing a limit get an in-product notice and can switch to Auto mode or another model.
• Microsoft does not state the limits. This follows its broader Copilot pricing changes, which we covered on 29 September.

What to do

• Check whether the Anthropic and OpenAI subprocessors are enabled in your tenant, and decide on purpose rather than by default.
• Review the data-protection terms that apply when each subprocessor is on, including where the data is processed, and update your records of processing.
• Set or review spending limits for usage-based billing before Cowork and Copilot Studio users start choosing these models.
• Tell users which models are approved for which kinds of data.

Sources

• Microsoft 365 Message Center MC1483844: Microsoft Copilot: new AI models beginning to roll out today (public archive copy; updated 1 October 2026) - 30 September 2026