The end of blind trust in third-party models
Microsoft has been one of the largest customers of external AI models to date. It invested 13 billion dollars in OpenAI and has long been purchasing models from Anthropic to power its Copilot ecosystem. But now, according to Bloomberg, it is starting to rely on itself.
Internal models called MAI are already running in two of the world's most widely used office applications — Excel and Outlook. They are replacing tasks previously handled by models from OpenAI (GPT) and Anthropic (Claude). This marks the first operational shift by Microsoft away from external AI suppliers within its flagship commercial software.
Why Microsoft is changing strategy
The reason is economic. Running AI features for hundreds of millions of Microsoft 365 users is not cheap. Every query that goes through the OpenAI or Anthropic API costs money. At scale, with tens of millions of users per day, fractions of a cent turn into hundreds of millions of dollars annually.
Mustafa Suleyman, head of Microsoft's AI division, previously indicated that the company plans to reduce and eventually eliminate spending on Anthropic's models. Moreover, some promotional phases of the OpenAI partnership are beginning to expire, freeing Microsoft's hands to deploy its own solutions more aggressively.
According to Bloomberg, MAI models already handle tens of thousands of user queries per week. While this still represents only a fraction of Copilot's total traffic, it proves that the internal models are sufficiently capable for real-world deployment in a production environment.
What MAI models can do and where they're heading next
MAI (Microsoft AI) is a family of proprietary models developed in-house. Microsoft is quiet about their architecture, but according to available information, these are large language models optimized for specific product scenarios — not general-purpose chatbots like ChatGPT or Claude.
Deployment is not limited to Excel and Outlook. Microsoft has already started integrating its own AI into GitHub Copilot, its flagship product for assisted programming. In the coming months, it plans to deploy an internally developed speech-to-text model into the Microsoft Teams platform.
For context — GitHub Copilot has over 50 million users and has become one of the fastest-growing AI products in history. Switching to its own models at this massive scale could save Microsoft hundreds of millions of dollars annually.
What it means for OpenAI and Anthropic
For OpenAI, this is unpleasant, though not surprising, news. Microsoft was not only its largest investor but also its largest customer. Losing even a partial volume of API calls from Microsoft 365 represents a significant revenue hit. OpenAI has been preparing for this eventuality — it recently established direct relationships with enterprise customers and is expanding into AI agents and financial services.
For Anthropic, it is another signal that relying on Microsoft as a key customer was not a sustainable long-term strategy. Suleyman's statement about "eliminating spending on Anthropic" gives this shift a clear timeline.
Interestingly, while Microsoft is stepping away from OpenAI and Anthropic, Anthropic itself is meanwhile testing chips from Microsoft as an alternative to Nvidia. Relationships among tech giants in the AI era are simply becoming more complex and less transparent.
Stock reacts positively
The market received the news with optimism. Microsoft's stock gained approximately 2% after the information was made public. Investors view cost savings on AI infrastructure as a step in the right direction — especially at a time when AI spending at major tech companies reaches tens of billions of dollars annually.
Microsoft has lost about 20% of its value over the past year, so any signals of improving unit economics are welcomed by investors.
Impact on Czech companies and users
For Czech businesses and individuals using Microsoft 365 and Copilot, nothing changes in the short term — the functionality remains the same, it's just now powered by Microsoft's internal models instead of GPT or Claude. In the long run, however, this transition could mean lower prices for end customers, since Microsoft won't be paying a margin to external suppliers.
Copilot for Microsoft 365 is available in the Czech Republic as part of Microsoft 365 Business Standard and Premium subscriptions for an additional fee of approximately 30 USD (around 700 CZK) per user per month. GitHub Copilot is available for free in the basic tier, with paid plans starting at 10 USD per month. However, neither of these products is localized into Czech yet — both the interface and communication are in English, or other global languages.
Does this mean Microsoft is completely ending its partnership with OpenAI?
No. Microsoft remains OpenAI's largest investor with 13 billion dollars and continues to use GPT models in the Azure OpenAI Service product. This is a gradual rollout of its own models where it makes economic sense — particularly for routine, high-frequency tasks in office applications. The strategic partnership with OpenAI continues; only its intensity in specific product scenarios is changing.
Are Microsoft's MAI models as powerful as GPT-5.5 or Claude Opus 4.8?
Microsoft has not published any benchmarks for its MAI models, so a direct comparison is not possible. However, it can be assumed that for specialized tasks in Excel and Outlook (data analysis, email summarization, formula generation) they are sufficiently capable — otherwise Microsoft wouldn't deploy them in production. For more complex tasks such as advanced programming or creative writing, external models will likely continue to be used.
When will the change be noticeable for regular Microsoft 365 users in the Czech Republic?
The transition is already underway, but it is virtually invisible to the end user — the functionality remains the same. The only difference you might notice is a potential change in the quality or speed of responses for certain AI features in Excel and Outlook. Microsoft is gradually testing these transitions and evaluating feedback.
