Sony is pretty cool about supporting the open source community by contributing code back to AOSP and helping developers tinker with devices. So it's no surprise that the company has already dropped source files for the Xperia Z Ultra.
The Xperia Z Ultra is, of course, a very large phone. It's not just big like other phones are big – it's obscenely large. The Z Ultra has a 6.4-inch 1080p screen, and it's not a tablet, it's a phone.