We recently reported on the latest firmware build (14.2.A.1.144) that had been certified for the Xperia Z1, Z Ultra and Z Compact. This was only certified on the European LTE variants, suggesting it was a likely carrier update, much like the 14.2.A.1.142 update.
Well the new ‘144’ firmware build has started to roll on the Xperia Z1 (C6903), but only with Movistar in Spain. The update probably brings small carrier-optimised changes. We would hope that the next global update for these handsets will be the Android 4.4.2 KitKat build, although Sony has so far not communicated any timelines for release.