Microsoft is routing work inside GitHub Copilot, Excel and Outlook away from OpenAI and Anthropic models, towards its own MAI family. Satya Nadella explained the shift on X: use frontier models only for frontier problems, push everything else to cheaper in-house models. Microsoft's Excel model matches GPT 5.4 at 10 times the efficiency.
Copilot Chat and PowerPoint are next in line.
Summary from source