Microsoft built its own AI to cut its OpenAI bill
By Chatday Editorial Team ·
For years, Microsoft’s AI strategy could be summed up in two words: pay OpenAI. The ChatGPT-maker powered Copilot, Windows, Office, the lot. This week that changed. At its big developer event, Build 2026, Microsoft showed off MAI-Thinking-1: its very first AI “brain” built entirely in-house, without OpenAI’s help. It’s a quiet but huge shift.
What Microsoft actually announced
MAI-Thinking-1 is what’s called a “reasoning” model, the kind that pauses to think through a problem step by step before answering (we explained why AI now thinks before it answers if you want the backstory). The headline isn’t really the model itself, though. It’s how it was made: Microsoft says it was trained from scratch, without learning from OpenAI’s ChatGPT in any way.
In plainer terms: until now, Microsoft was renting the engine that powered most of its AI features. Now it has built its own.
Why Microsoft wants its own AI
Two reasons, and they’re both easy to understand:
- Money. Paying OpenAI to run AI across Windows, Office and Copilot costs a fortune. An in-house model Microsoft controls can be far cheaper to operate at that scale.
- Control. Relying on one supplier for something this important is risky. Owning the technology means Microsoft isn’t at the mercy of a partner’s prices, rules or roadmap.
Reportedly, MAI-Thinking-1 is a “big but efficient” model, large enough to be genuinely smart, designed to be cheaper to run than the frontier models it’s meant to replace. Treat the exact specs as preliminary until Microsoft publishes the full details.
Hold on, is Microsoft dumping OpenAI?
No, and this is the part the headlines often miss.
| What’s changing | What’s staying the same |
|---|---|
| Microsoft now has its own in-house AI brain | Microsoft’s cloud still runs OpenAI’s models |
| It can shift some features off OpenAI to cut costs | Copilot and Office still use OpenAI too |
| Less dependence on a single supplier | The partnership continues, just less exclusive |
So it’s less a breakup and more Microsoft making sure it’s never only dependent on one company. Smart business, not a soap opera.
The bigger picture: everyone wants their own AI
Microsoft isn’t alone. Across the industry, the companies that built their products on top of someone else’s AI are racing to build their own, to cut costs and avoid being locked in. Apple’s reportedly leaning on Google’s Gemini for the new Siri, Amazon’s pushing its own models, and now Microsoft has joined the “build, don’t just rent” club.
For you, the takeaway is simple: the number of genuinely good AI models is exploding, and no single company owns “the best” one anymore. Which is exactly why it pays to be able to try them side by side.
Or just start a chat with each and feel the difference:
What it means for you
Day to day, nothing breaks. Copilot keeps working. But this is another sign of where things are heading: more competition, lower prices, and more choice. The winners are the people who don’t tie themselves to one model and instead pick the best tool for each job.
The lesson from Microsoft’s move applies to you too: don’t bet on a single AI. In Chatday you can chat across GPT-5.5, Claude and Gemini in one place and switch whenever one fits the task better, free to start.