Sony Mobile has released the first firmware update for the Xperia XZ Premium, which updates the handset with the latest 1 June 2017 Android security patch. Build number 45.0.A.5.1 has been released a number of regions, but there are also a couple of other firmware versions released concurrently with the same Android security patch.
This includes build number 45.0.A.5.6 for the single SIM Xperia XZ Premium (G8141) released in Korea, and version number 45.0.A.5.8 for the dual SIM version (G8142) in Taiwan. No other big changes are included in the update.
Thanks Dennis, Stanley and Walaspancha!