Sony has released information about it's latest mobile phone, the Xperia Z4 on their Japanese website.
The Xperia Z4 has a 5.2-inch screen (similar to the Z3) and is 6.9mm thick. It is powered by a eight-core, 64-bit Snapdragon 810 processor. It also has a massive 3GB of RAM and runs on Android 5.0 Lollipop OS. Unique features includes the 20.7MP front and rear cameras, so be prepared for some ultra detailed selfies.
Like it's predecessors, the Xperia Z4 is also water and dust resistant. Something that both the iPhone 6 and the Samsung S6 don't have.
No news yet on prices and launch date. As far as I know, the Z3 sales were not that good despite all the positive reviews. I guess it has something to do with the price and the fact that Sony is no where near Apple in terms of brand desirability.
I really like the Xperia Z3 compact. However, no news on a compact version of the Z4 yet.