Microsoft has started replacing OpenAI and Anthropic models with its own AI systems in products including Excel and Outlook, marking a new step in the company’s push to reduce the cost of running AI across its software business, according to a Bloomberg report.

Tens of thousands of prompts in the spreadsheet and email apps are now being completed each week by Microsoft’s internally built MAI models, according to a person familiar with the work. The apps previously relied more heavily on models from OpenAI and Anthropic.

The shift remains small compared with Microsoft’s overall AI usage, but it shows the company is moving more of its AI workload onto systems it controls. That matters as Copilot expands across Microsoft 365 and drives higher demand for compute and model access.

Microsoft currently benefits from its long running OpenAI partnership, which gives it access to advanced models at favorable economics. But the company is preparing for a future where outside AI labs can charge more for their models, especially as enterprise demand grows.

Microsoft AI chief Mustafa Suleyman said in June that the company wanted to reduce spending on Anthropic by using more MAI models. “We pay a lot of money to Anthropic, so our goal is to reduce and ultimately eliminate that cost,” he said at the time.

The company announced seven new AI models at its Build developer conference in June, including one it says can match the coding abilities of Anthropic’s Opus 4.6 at lower cost. Microsoft’s MAI models are also available in GitHub Copilot, while a Microsoft built transcription model is expected to be used in Teams and other products in the coming months.

The move does not mean Microsoft is cutting off OpenAI or Anthropic. Instead, it points to a more mixed model strategy, where Microsoft uses outside systems for high end tasks while shifting cheaper or more routine workloads to its own models.

For Microsoft, the goal is simple: keep Copilot growing without letting model costs dictate the economics of the business.