Microsoft is tired of paying the high price of admission for third-party AI. In a bid to slash computing costs, the tech giant is starting to swap out OpenAI and Anthropic models in favor of its own home-grown tech inside Excel and Outlook.

According to sources familiar with the matter, Microsoft’s internally developed “MAI” models are already handling tens of thousands of AI prompts every week across its email and spreadsheet applications. It’s a milestone that hasn’t been reported until now. While it’s still a drop in the bucket compared to Microsoft’s overall AI footprint, it proves that the company’s push to build cheaper, highly competitive AI is actually working.

Right now, Microsoft’s deep pockets and partnership with OpenAI give it a massive discount on the computing tokens powering Copilot. But that deal won’t last forever. AI division chief Mustafa Suleyman is determined to ensure Microsoft isn’t left at the mercy of whatever price hikes independent labs decide to throw their way. Suleyman wasn’t shy about the strategy at June’s Build conference, stating bluntly: “We pay a lot of money to Anthropic so our goal is to reduce and ultimately eliminate that cost.”

The transition is already expanding. Beyond Office, MAI models are cropping up in GitHub Copilot, and Microsoft plans to roll out a proprietary transcription model for Teams in the very near future.