1 Big screen
The Z4 is said to have a bigger screen than the Z3, though accounts vary as to its actual size.
One source told PhoneArena it will sport a 5.2-inch, 1080p display. However, a previous report claimed it will be a 5.4-inch QHD screen.
Both of these are improvements on the Z3's 5.15-inch display.
Reading the tea leaves, we would wager the 5.4-inch, QHD screen is more likely.
Screens are getting bigger and sharper, and ever since the LG G3 launched last year, QHD (aka 2K) is quickly becoming standard for flagships.
The LG G4 is said to boast a 3K screen. With standards evolving so quickly, it's unlikely Sony would stick with bog-standard 1080p.
2 New camera
Back in November, Sony unveiled a new camera module for use in mobile devices. And where better to implement it than with the Z4?
The module is called the Emor RS IMX230. It's the first for a smartphone to feature image plane phase detection autofocus.
In other words, it's very nippy at capturing quick-moving objects for both stills and video.
This is handled by dedicated phase detection autofocus pixels which are incorporated into the screen of the image sensor and track the distance to the subject.
It supports up to 192 focus points.
It's smaller than the sensor in the Z3 – meaning the Z4 could be slimmer – and captures HDR videos at full 4K.
3 Plenty of RAM
Again, reports vary as to how much grunt we can expect in the Z4. But rest assured, it will be plenty.
One reports pegs it with 4GB of RAM, while another says 3GB. Samsung's Galaxy Note 4 has 3GB of RAM, and that whips through tasks quick as you like.
4GB would be almost obscene.
4 A bigger version?
As with previous Xperia Z devices, Sony is said to have a bigger version in the pipeline too.
Named the Xperia Z4 Ultra, it's said to have a 5.9-inch screen, with 4GB of RAM and a 16-megapixel camera.
That all sounds correct apart from the camera.
The Z4 will sport a 21-megapixel snapper, so why would Sony downgrade the camera on the bigger, more expensive model?
5 Nippy chip
Again, reports vary as to which processor will be inside the Z4. Early rumours said it would have Qualcomm's Snapdragon 805 chip, while subsequent whisperings sided for the newer and faster 810.
Either way, expect it to be mighty fast.
Android 5.0 Lollipop is also a dead cert.
It might only be on less than 2 per cent of Android devices at the moment, but it's the OS version du jour for new flagships.