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.
Comparing the D6503 and the Sony Xperia Z1
1. D6503 on left and Sony Xperia Z1 on right
2. Ports have different locations
3. D6503 has speaker on top
4. D6503 speaker on bottom
5. No speaker on top of Xperia Z1
source: XDA via XperiaGuide