The phone has been leaked over the XDA's forums and bears the model number D6503. This smartphone is largely being touted as the refresh of the Sony Xperia Z1. As per XDA Forums user iRimas, the said phone sports a 5.2-inch display. It is currently running on android 4.3 (the user notes that it is an old build and the device should offer Android 4.4 KitKat out of the box) and has a brand new UI on board. As per the leaked images, the said phone will have thinner bezels than Sony Xperia Z1.
The user also notes that as of now the device is pretty unstable and the UI keeps crashing. The screenshot of this smartphone reveals that it is powered by a Snapdragon 800 (MSM8974-AB chipset with a quad-core 2.3GHz Krait 400 CPU, faster Adreno 330 GPU and will also have 3GB of RAM.
Even the earlier rumours had suggested that the Sony Xperia Z2 (or whatever Sony plans to call the successor of Sony Xperia Z1) will come with a 5.2-inch display and have a resolution of 2560x1440. Furthermore, it will have a 20.7MP camera, and a 3700mAh battery.
The leaks have also revealed that the Sony Xperia Z1's successor carries the code name Sirius. Even @evleaks had suggested that the Sony Xperia Z1's successor will pack in a 5.2-inch display and Qualcomm's quad-core MSM8974AB SoC processor.
So we have little reasons to suspect that this smartphone is not Sony Xperia Z1 sequel. However, folks at Android Headlines point out that from the model number it appears to be the successor of the Sony Xperia ZL rather than the Sony Xperia Z1.
In all probability, we are hoping that Sony might be looking at unveiling this smartphone at the Mobile World Congress (MWC) 2014, which is when we expect the suspense to end. [ Android Headlines and GSM Arena via XDA Forum]