The Google Play edition phones use a stock Android OS, making it quicker to update than unlocked and carrier versions. The updates are sent out directly from Google. A wide range of devices, from flagship models to the Motorola Moto G, now offer a Google Play edition, which can be purchased from the Google Play Store.
Sony hasn't confirmed that the update is coming, so the Japanese manufacturer has not yet revealed a date when Android 4.4.3 will be pushed out to the device.
Bluetooth SIG reveals that Android 4.4.3 is coming soon to the Sony Xperia Z Ultra Google Play edition
source: BlueoothSIG via BlogofMobile (Translated), XperiaBlog, AndroidCentral