Microsoft Quietly Routes Some Excel and Outlook Prompts to Its Own MAI Models
Bloomberg reports tens of thousands of weekly prompts in Microsoft's flagship apps now run on in-house models — a small but strategic shift away from paying OpenAI and Anthropic per prompt.
Microsoft is now completing tens of thousands of AI prompts each week in Excel and Outlook using its internally built MAI models instead of OpenAI or Anthropic models, Bloomberg reported July 7 (reprinted by the Seattle Times). The change is server-side, affects a small share of total volume, and produces no visible interface change.
Context
Microsoft is simultaneously OpenAI's biggest distribution partner — GPT-5.6 became the preferred model in Microsoft 365 Copilot two days after this report — and its most motivated competitor on model economics. AI chief Mustafa Suleyman said at Build in June: "We pay a lot of money to Anthropic — so our goal is to reduce and ultimately eliminate that cost." Bloomberg reported Microsoft's Anthropic spend at roughly $500 million per year as of January 2026.
What changed
- Selected Excel and Outlook prompt traffic now runs on MAI models rather than partner models.
- Seven MAI models were announced at Build; MAI is already present in GitHub Copilot, and MAI transcription is heading to Teams.
- Microsoft declined to comment on the report.
Why it matters
Even OpenAI's closest partner will not accept single-vendor economics. Model routing — picking the cheapest adequate model per workload, invisible to the user — is emerging as the enterprise endgame, and Microsoft's move gives it both cost leverage and negotiating leverage over OpenAI and Anthropic. The simultaneous "preferred model" designation for GPT-5.6 and the MAI swap are complementary, not contradictory: preferred status sets the default, while routing optimizes the margins.
Details
The affected volume — tens of thousands of prompts weekly — is small relative to total Copilot usage. No accuracy or quality comparison between MAI and the displaced models has been published for these workloads.
Limitations and caveats
This rests on a single Bloomberg report (though reprinted by multiple outlets), with Microsoft declining comment. The $500 million Anthropic-spend figure is Bloomberg's estimate as of January 2026. The precise share of Copilot traffic on MAI models is unknown.
Sources
- Seattle Times (Bloomberg reprint) — Microsoft replaces OpenAI, Anthropic with own AI in some apps (reputable press)
*Update note: This post was last reviewed on 2026-07-22. Watch Microsoft's earnings commentary for MAI adoption metrics.*
Sources
Drafted with AI assistance from source briefs; reviewed for citation completeness and label accuracy.