The situation is in flux, but right this second we expect the D6503 to feature a 5.2 inch screen with a 1080 x 1920 resolution. A quad-core Snapdragon 800 MSM8974AB processor is under the hood, supporting 4k video playback. There is 3GB of RAM inside with 16GB of native storage on board. Android 4.4.2 is pre-installed out of the box.
We have some side-by-side pictures to show you that reveal the difference between the Sony Xperia Z1 and the Sony D6503. The latter is a bigger device with a larger screen and larger dimensions, while the positions of some of the ports are different. The speakers are also placed in different locations.
The Sony D6503, aka Sirius, is a beast regardless of whether it is merely a Z1 refresh, the Xperia Z2 or some other device. Check out how the model compares to the Sony Xperia Z1 in the slide show below.
source: XDA via XperiaGuide