Bloomberg: Microsoft has started replacing OpenAI and Anthropic models with its own MAI models in Excel and Outlook. Tens of thousands of prompts a week already moved

Bloomberg reported yesterday that Microsoft has quietly begun routing part of the Copilot workload inside Excel and Outlook to its own MAI models instead of OpenAI or Anthropic. The in-house models are already handling tens of thousands of prompts a week across the two apps. Microsoft stock rose 1.75% on the day, so the market read it as a margin story first.

Why this matters more than the raw number suggests: Copilot inside the productivity suite is Microsoft's single highest-volume AI surface, and until now most of that traffic paid a bill to a third party. Moving even a slice of it to models Microsoft owns end to end changes the unit economics of bundling AI into Office at all.

It is also the first visible off-ramp for the OpenAI relationship inside shipping products. Excel and Outlook were previously described as relying heavily on OpenAI and Anthropic models. This is the first account of the in-house alternative running as a live production replacement rather than a research bet or a supplementary option.

Source: https://www.bloomberg.com/news/articles/2026-07-07/microsoft-replaces-openai-anthropic-with-own-ai-in-some-apps