Microsoft replaces OpenAI and Anthropic with its own MAI models in Excel and Outlook

Microsoft is swapping parts of Copilot’s usage in Excel and Outlook from external AI providers to its own MAI models to reduce inference costs. As of 7 July 2026, Microsoft began routing a meaningful share of Copilot prompts in those two productivity apps to internally built MAI models. The change targets high-volume, routine tasks such as summarizing an email thread, drafting replies, and formatting spreadsheets, with “tens of thousands of prompts weekly” handled by MAI inside Excel and Outlook. Microsoft said this is not a complete departure: OpenAI’s frontier models remain available for complex, demanding work, and Anthropic models continue embedded in specific Office applications for selected use cases. The MAI models were introduced at Microsoft’s Build conference in June 2026, when Microsoft unveiled MAI-Thinking-1 and MAI-Code-1-Flash. The shift matters commercially because any reduction in external prompt volume could improve Microsoft’s unit economics and potentially narrow OpenAI and Anthropic inference revenue.