According to Play - one of Poland’s major mobile carriers - its Sony Xperia Z should be updated to Android 4.4.2 KitKat in late February, or March. If that turns out to be accurate, Xperia Z owners in other parts of the world should expect to get the new version of the OS at about the same time. The Xperia Z turned 1 year old last month, and a KitKat birthday present would be really nice.
Alongside the Xperia Z, other slightly older Sony Android devices that will likely be updated to Android 4.4 KitKat later this year are the Xperia ZL, Xperia ZR, and the Xperia Tablet Z. Naturally, the newer Xperia Z1 and Z Ultra will also be updated, possibly starting the next few months.
source: BlogPlay (translated) via Xperia Blog