Microsoft is shaking up its AI strategy by integrating Anthropic’s Claude Sonnet 4, alongside its long-standing reliance on OpenAI’s GPT models across Office 365.

The move comes after internal tests found Sonnet 4 outperforms GPT-5 in several important areas.

Such as handling complex spreadsheet automation in Excel and generating more visually appealing PowerPoint presentations.

Microsoft is still describing OpenAI as its “frontier partner”.

But OpenAI’s CEO, Sam Altman, could be excused for feeling concerned.

This pivot aligns with earlier efforts by Microsoft to diversify its AI stack.

As far back as December 2024, the company began exploring internal and third-party models, including its own and others like DeepSeek, to reduce dependence on OpenAI and improve cost-efficiency.

By incorporating Claude Sonnet 4, Microsoft is expanding that strategy into critical productivity tools.

To use Claude Sonnet 4 inside Office 365, Microsoft will have to pay Amazon Web Services (AWS), since Anthropic runs its models on Amazon’s cloud.

AWS is one of Microsoft’s fiercest rivals in the cloud-computing market.

Once dominant, OpenAI now has the likes of Anthropic nipping at its heels

Microsoft assures users that the pricing for Copilot within Office 365 will remain unchanged. It seems the company, like many in the tech industry, is willing to eat the cost of providing cutting-edge AI to customers.

At least for the time being.

But the expansion of Microsoft’s AI portfolio signals a more diverse future for Office intelligence – the intelligence layer Copilot adds across the Office suite.

Office intelligence is the suite of smart features in Word, Excel, PowerPoint and Outlook that help users draft text, analyse data, design presentations and manage email.

In practice, this means that Office users can benefit from combining different AI models to make these everyday tasks faster, smoother, and more polished.

If Claude can indeed elevate presentations and crunch numbers better, businesses may enjoy sharper tools without enduring a price hike.

Anthropic has declined to comment, as has OpenAI.

There’s no public release timeline yet, but Microsoft will presumably reveal the details in the coming weeks.