It appears that the Sony Xperia Z4 Tablet is expected to get the update to Android 6.0 Marshmallow on June 16th, at least in the versions sold by carrier KDDI and au. The SOT31 codenamed version of the slate is the one getting updated.
This update comes via OTA or via PC connection, or via LTE, if you want to waste gigabytes. The software package takes up 1.5 GB if you’re doing it wirelessly and for some reason the package offered via PC takes up a big 2.7 GB. After the update, the slate will reach build version 32.1.C.0.281. As usual, Marshmallow brings Doze, Google Now on Tap, improved permission management and improved storage and RAM management.
Bug fixes, security updates and more tweaks will be provided. It’s not very clear what happens with the Stamina mode, that has been an on and off love affair till now for Sony. I guess that by this point, all the mainstream Xperia tablets already have Marshmallow, right?