GPT-6.1 Sol and Claude Sonnet 5.5 come to Microsoft Copilot

Microsoft said on 30 September 2026 that OpenAI's GPT-6.1 Sol and Anthropic's Claude Sonnet 5.5 are joining model choice in Microsoft Copilot. They follow Claude Opus 5.5 and GPT-6 Sol, added earlier in September. Both began rolling out that day in Copilot Cowork and Copilot Studio, with usage-based billing. Microsoft said a phased rollout to Word, Excel, PowerPoint and Chat would begin "in the coming week" as part of the user subscription licence. There, usage limits apply. Microsoft says the vast majority of users are not expected to reach them; users are warned as they get close and can switch to Auto or pick another model. Availability and usage may vary by licence, access and region. Microsoft points to its AI at Work Roadmap and Copilot release notes for the latest status. Sorted take: if your team already has Copilot licences, two newer models may appear in the model picker in your Office apps. Try each on one real task before changing defaults, and watch spend in Cowork and Studio, where these models are billed by usage.