Microsoft starts swapping its own MAI models in for OpenAI and Anthropic in Excel and Outlook

Microsoft has begun replacing OpenAI and Anthropic models with its internally built MAI models in parts of Excel and Outlook, which now complete tens of thousands of AI prompts weekly. AI chief Mustafa Suleyman said in June the goal is to "reduce and ultimately eliminate" what Microsoft pays Anthropic; at Build it announced seven MAI models, including one it claims matches Anthropic's still-popular Opus 4.6 on coding at lower cost. The shift is incremental — OpenAI and Anthropic still handle most Copilot production traffic, and the partnerships continue.

Why it matters

The largest distributor of frontier AI is becoming its own supplier where the economics work — the classic private-label move, applied to model inference. For OpenAI and Anthropic the risk isn't losing Microsoft's headline traffic; it's the margin story if commodity-tier prompts get insourced everywhere while only frontier work stays external. "Good enough at lower cost" is the same wedge reportedly driving US firms toward cheaper Chinese models — Microsoft is just running it internally.