Microsoft has started routing some Copilot requests in Excel and Outlook through its own MAI models instead of OpenAI's or Anthropic's, Bloomberg reported this week. Tens of thousands of prompts per week now run on the in-house family, which the company launched in early June. It is a small fraction of total Microsoft 365 traffic. It is also the first time Microsoft has admitted the swap is happening in shipping products.
Why now
Cost, mostly. Every Copilot response burns compute, and Microsoft pays OpenAI and Anthropic for the privilege at a scale that has turned into a real line item. The company still gets discounted access to OpenAI through its partnership, but that arrangement does not last forever, and MAI chief Mustafa Suleyman has been unusually blunt about where this goes. In June he said Microsoft pays Anthropic a lot of money and wants to reduce and ultimately eliminate that cost.
That is a strange thing to say about a company whose Claude models Microsoft deliberately embedded in Copilot as a selling point. The official line is that the partnerships continue and Copilot is becoming a multi-model platform that picks the cheapest good-enough model per task. Read it the other way and OpenAI and Anthropic just got demoted from default plumbing to premium option.
The parity claim is Microsoft's, not the world's
At Build 2026, Microsoft introduced seven MAI models, led by MAI-Thinking-1, a 35-billion active parameter reasoning model with a 256K context window. The company says independent raters at Surge preferred it to Sonnet 4.6 in blind side-by-sides, and that it lands alongside Opus 4.6 on coding.
Worth reading the fine print. That coding claim rests on a single number, 53% on SWE-Bench Pro, run through Microsoft's own harness, according to the keynote transcript. The human preference test that supposedly beats Sonnet was also commissioned by Microsoft. None of this is disqualifying, every lab grades its own homework, but "matches Opus on coding" and "we picked one benchmark where we tie Opus" are different sentences.
What it means for your subscription
Possibly nothing you can see. For anyone using Copilot in Word or Outlook, the interface does not change; only the model underneath does. Microsoft has announced no pricing changes tied to the rollout and no timeline for how much traffic eventually moves in-house.
The uncomfortable version, floated in Bloomberg's reporting, is that you keep paying the same $30 per user per month while the AI behind it quietly gets cheaper for Microsoft to run. CEO Satya Nadella has also hinted at a shift toward usage-based billing rather than flat subscriptions. One plausible setup: MAI models as the default, Claude and GPT as paid add-ons, with Microsoft's third-party bill passed straight to whoever wants the frontier stuff.
The MAI models are already in GitHub Copilot, and Suleyman said a Microsoft transcription model is headed to Teams in the coming months. Whether "good enough" holds up once these things handle more than a rounding error of real traffic is the part nobody can benchmark yet.
