Sony has an event planned at the Mobile World Congress on March the 3rd where we will see some new products launched, but it appears they have accidentally leaked the Xperia Z4 themselves.
According to an appearance on the official Xperia Lounge application, the tablet is (predictably) called the Xperia Z4 Tablet and features a 2K display, along with an “ultra fast processor.”
The post has since been pulled, but not before the folks at Xperia Blog managed to snag a screenshot showing off a side view of the tablet, pictured below.
There wasn't much else revealed outside of the references to the display and processor. However, the post does note that the tablet will be shown off during Mobile World Congress on March 3.