Earlier this week, Bloomberg reported that Microsoft was swapping out some of OpenAI's software for its own internal models, aiming to reduce expenses. These proprietary models, called MAI, were reportedly being used more frequently to run apps like Word and Excel. This development raised a recurring question about the two companies, which once seemed inseparable but have recently sent mixed signals about the state of their relationship: Were they growing apart?

Now, OpenAI is trying to put any suggestions of a split to rest. During OpenAI's launch of GPT 5.6 on Thursday, the company announced that it would become the "preferred model" powering Microsoft's 365 Copilot. In a blog post published Thursday, OpenAI noted that GPT 5.6 would support Microsoft users across its suite of productivity applications, including Word, Excel, PowerPoint, and Cowork.

"Our partnership with Microsoft has always been about bringing the benefits of advanced AI to more individuals and organizations, and we're excited to continue building on that shared commitment," OpenAI wrote in the post.

What exactly being a "preferred model" means is not entirely clear, other than that OpenAI's software will continue to run Microsoft's apps. That said, it was never reported that ChatGPT's software would stop powering Microsoft's apps—only that Microsoft was increasingly relying on its own software to cut costs. The new "preferred model" disclosure doesn't seem to contradict that earlier reporting.