The software giant is routing productivity app AI prompts to in-house models to cut inference costs and reduce reliance on outside providers
Microsoft has quietly started swapping out the AI brains behind Excel and Outlook. As of July 7, 2026, the company began routing a meaningful share of Copilot prompts in those two apps to its own internally built MAI models, stepping back from its reliance on OpenAI and Anthropic for the kind of everyday, high-volume tasks that add up fast on an inference bill.
What is actually changing #
The MAI models, short for Microsoft AI, are now handling tens of thousands of prompts weekly inside Excel and Outlook. These are the bread-and-butter requests: summarizing an email thread, drafting a reply, formatting a spreadsheet, that sort of thing.
Microsoft has been clear that this is not a full divorce from its external partners. OpenAI’s frontier models will continue to power more complex, demanding tasks where raw capability still matters. Anthropic’s models also remain embedded in specific Office applications for select use cases.
The MAI models themselves were introduced at Microsoft’s Build conference in June 2026, where the company unveiled MAI-Thinking-1 and MAI-Code-1-Flash as part of a broader push to establish its own presence in the AI model landscape. The Build showcase framed these models as competitive in quality while being cheaper to operate.
Why this matters beyond the product update #
Microsoft’s relationship with OpenAI is one of the most closely watched partnerships in tech. Microsoft has poured billions into OpenAI over several years, and that investment gave it early access to GPT models that became the backbone of Copilot.
Running AI at the scale Microsoft does, across hundreds of millions of Microsoft 365 users, means inference costs are not a rounding error. Every prompt routed to an external provider is a fee. Building in-house models that are good enough for routine tasks is one of the more straightforward ways to solve it.
What investors should watch #
Routing routine prompts to cheaper in-house models means higher margins on each Copilot seat sold, which is a straightforward positive for the unit economics of the business.
The more interesting question is what this means for OpenAI’s revenue picture. Microsoft is OpenAI’s largest customer and primary cloud partner. If Microsoft progressively shifts more prompt volume to MAI models, OpenAI’s inference revenue from that relationship narrows. OpenAI has been expanding its own direct enterprise relationships and consumer products to diversify away from that dependency.
Anthropic faces a similar dynamic. Its models remain in specific Office applications for now, but the logic that pushed Microsoft toward in-house alternatives for Excel and Outlook can easily extend to other products.
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