Sony Xperia Z4 sneaks out in Japan and fails to thrill

This is Sony's latest flagship smartphone, and it's really hard to tell the difference

The names' Z4, Xperia Z4. Licence to... be very similar to the Xperia Z3 in almost every way. That's right, Sony has a new flagship smartphone, but only in Japan.

There's been a lot of talk about the Sony Xperia Z4 and we've now seen the handset launch relatively quietly in Japan.

Read more: Sony Xperia XZ3 review: a quality Android flagship with stunning Bravia-engineered display

Arriving a little over six months after the launch of the Xperia Z3 - Sony's current incumbent at the top of its mobile range - the Xperia Z4 makes just a few minor changes to its predecessor.

The main talking points are the new octa-core Snapdragon 810 processor which should give you more power - but there are concerns about it overheating - a slimmer profile (down from 7.3mm to 6.9mm) and a new wide angle front facing 5.1MP selfie camera.

The 5.2-inch full HD display remains the same, as does the 3GB of RAM, 20.7MP rear camera, 128GB microSD slot and IP68 water and dust proofing.

Battery woe?

There's a slight concern regarding battery life, as the slimmed down aluminium body means Sony has had to ditch the 3100mAh power pack from the Z3 in favour of a 2930mAh offering in the Xperia Z4. Hm.

Available in white, black, copper and aqua green there's currently no word on its price or potential release outside of Japan - so you're stuck with the Z3 for now.