A new firmware update with build number 10.5.1.A.0.283 has been certified by the PTCRB website for a number of handsets including the Xperia Z, Xperia ZL, Xperia ZR and Xperia Tablet Z.
There is a good chance that this new build will bring Android 4.4.4. A recent schedule update from Australian carrier Telstra confirmed that the Android 4.4.4 platform update was heading to the Xperia Z. Whatever this update turns out to be, it should start rolling within a few weeks.
The following platform update for the Xperia Z appeared on the Telstra website recently.
Thanks Karim, Markus, Nawi_88, Saper and SiF!
