Some leaked images of a Lumia 930 running an unknown Windows Phone build show split-screen or multi-window multitasking UI that even our sources believe will come eventually to Windows 10 for Phones. We though need to take it with a pinch of salt though, as the device in images doesn’t seem like running Windows 10 for Phones as is clear from the icons seen in the status bar on the top. So only possibility is these screenshots belong to some advanced version of Windows Phone 8.1 GDR2, that is like a bridge between Windows Phone 8.1 GDR1 and Windows 10 for Phones in terms of UI changes.
We have also reported that there may be a minimum display size for being able to use multi-windows feature. Like, we have seen with movable keyboards, it may well be 5-inch.