The Xperia Z4 is a flagship, it retains the look of the Xperia Z3, only see few changes like the thickness. The Xperia Z4 is 6.4mm, having a metal frame visible on the sides of the phone.

As earlier said, the Smartphone comes with Android 5.0 Lollipop. The alterations is that it is powered by 64-bit octa-core Qualcomm Snapdragon 810 processor backed by 3 GB RAM. It has 20.7 MP primary camera and 5 MP front-facing camera. 32 GB internal memory, expandable to 128 GB via mircoSD cards is also available on the flagship.

The Xperia Z4 retains the IP6X, IPX5 and IPX8 certifications, which means the smartphone is dust-proof and can be submerged in water forever.
http://www.techrez.com/at-last-sony-officially-announces-the-xperia-z4/