Among the information Microsoft revealed at today’s Windows 10 event is the good news many were waiting to hear: Windows 10 will be a free upgrade for customers running Windows 7, Windows 8.1, and Windows Phone 8.1. That said, there are some caveats to this deal, not the least of which—as I understand it—is that those who agree to this upgrade must also agree to let their PCs and devices be kept up-to-date by Microsoft going forward.The notion here is “Windows as a service,” one that will in effect make version numbers much less important going forward. Technically, this should work a lot like Office 365, and with the same exclusions for businesses. Indeed, businesses are free (ahem) to continue moving forward with existing licensing schemes and controlling updates if they prefer.

But let’s get to that free bit.

As described by Microsoft, Windows 10 will be free for customers running Windows 7, Windows 8.1, and Windows Phone 8.1, albeit only during the first year of Windows 10’s life cycle. So it’s a promotional offer designed to get as many people as possible upgraded to the new OS version.

But consider this line: “Once a Windows device is upgraded to Windows 10, we will continue to keep it current for the supported lifetime of the device – at no additional charge.” This suggests to me that keeping Windows 10 up-to-date going forward is not optional. That in order to get this offer—or perhaps just to get Windows 10 as a consumer, regardless—will require you to let Microsoft keep your system up to date.

I’m further curious how this will work on phones, given the trouble Microsoft has had delivering updates on Windows Phone.