Pictures of the Sony D6503 leaked over the weekend and now having seen detailed information from the device, we are in a position to reveal more details. The Sony D6503 codename is confirmed as the Sirius and it will come with the Qualcomm MSM8974AB chipset with 2.3GHz quad-core processor and Adreno 330 graphics.
Other confirmed features includes a 5.2-inch 1080p display, 3GB RAM, 20.7MP rear camera and 2.1MP front camera. The display spec in the picture below of 4.86-inches refers to the size excluding the virtual buttons. If you gross that up, it appears that this display is indeed 5.2-inches.
The firmware build on the device is Android 4.3 relating to version number 17.0.A.0.228. However, this is from an old build of the device. We can reveal that newer builds come with firmware version 17.1.A.X.XXX which relates to Android 4.4.2 KitKat. Below you will find some screenshots relating to the Android 4.3 firmware of Sony D6503, which shows some changes to the UI. Remember, this is OLD firmware back from early November 2013. The handset itself will launch with Android KitKat, so expect some additional changes.
UI pics from XDA-developers.