The iPad Pro’s 12.9-inch screen doesn’t fit in with Microsoft’s “true mobile device” category. Why is this important? Because Apple’s most expensive tablet has become a bit more expensive . . . if you want to use Microsoft Office apps on it. And since it is a “productivity” device, Microsoft assumes you will, unless you go with the Apple version, Pages, Number, and Keynote.
As Ars Technica’s Peter Bright points out in his article, Microsoft defines a 10.1-inch cut-off: If your device has less than that threshold, it is a “true mobile device”, and as such it grants you access to Office apps for free.
If your device’ screen is above that threshold, it’s no longer a true mobile device, which means you need an Office 365 subscription.
Bright highlights the lack of relevant licencing or descriptive text, but Microsoft confirmed to Ars Technica that when run on the iPad Pro, Office apps will require an active subscription. More wording and clarification has yet to be completed; the software maker is currently busy finalizing it.