Sony is developing Android 5.1 update for Xperia Z Series
Whether a little "slow" but the fact Sony is one of the very few smartphone makers today still cared FW upgrade for certain models launched since the beginning of 2013 (over 2 years). Android 5.0 is still not the end, but the upcoming 5.1 also includes more Adroid.
According to Australia's Telstra network showed quite clear timetable for this. Accordingly, capable Android 5.1 update will arrive samples Xperia Z, Z1, Z1 Compact around August next. This means that international models will be updated earlier than August, of course, more advanced models like Z2, Z3..vv outside the list can not be updated.
Thank Sony for this interest.