Microsoft swaps OpenAI and Anthropic for its own AI in Excel and Outlook

Microsoft has quietly started routing AI requests in Excel and Outlook through its own models instead of OpenAI's or Anthropic's, reports Bloomberg. Tens of thousands of prompts per week are now handled by Microsoft's in-house MAI family, which the company launched in June 2026. If you use Copilot features in Microsoft 365, there's a real chance the AI behind them is no longer the one you'd expect.

The models

Microsoft unveiled seven new MAI models at its Build conference in June. The lineup includes a coding assistant and an image generator, but the headline claim is performance in spreadsheet tasks: Microsoft says its Excel-tuned MAI model matches GPT-5.4 on accuracy while running ten times more efficiently. That efficiency gap is the key driver here — more requests for less money.

CEO Mustafa Suleyman has gone further than most executives would in public, stating an explicit goal to eliminate Microsoft's costs from Anthropic entirely. That's a striking line given that Microsoft has spent years positioning its OpenAI partnership as central to the entire Copilot strategy. The company says it still works with both OpenAI and Anthropic and has not ended those relationships.

The broader shift

Microsoft isn't alone. TechCrunch reports that Amazon, Uber, Meta, and Accenture are all moving in the same direction — pulling more AI workloads in-house to reduce what they pay third-party model providers. For big tech, external AI bills have become a meaningful line item, and building or fine-tuning your own models is increasingly the cheaper long-term play.

For enterprise Azure customers, MAI is already available through Microsoft Copilot and Azure AI Foundry. The efficiency gains Microsoft is claiming — lower cost per query at comparable quality — could reduce the total cost of running AI across large Office 365 deployments.

What it means for users

For most people using Word, Excel, or Outlook, this change is invisible. The Copilot interface stays the same; only the model underneath shifts. Microsoft has not announced any pricing changes tied to the MAI rollout, and no specific timeline has been given for how much of the traffic will eventually move to in-house models. The scale disclosed so far — "tens of thousands of prompts weekly" — is a fraction of Microsoft 365's total usage across hundreds of millions of users.

The longer-term question is whether Microsoft's vertical integration play, pairing MAI models with its own Maia AI chips, gives it enough independence to meaningfully reduce its reliance on OpenAI — the company it still part-owns and publicly champions.