Microsoft 365 Copilot has switched from Anthropic’ s Claude to OpenAI's new GPT-5.6, the company's latest flagship model family, as the preferred AI model across Word, Excel, PowerPoint, Copilot Chat and Cowork. The change comes two months after Microsoft made Anthropic's Claude the default model in several of the same applications, and marks the latest shift in an ongoing contest between the two AI labs for position inside Microsoft's productivity platform.