The above question is the same one we posed when we saw firmware build 14.3.D.0.183 certified for the Sony Xperia Z1s (C6916) for T-Mobile. That build never saw the light of day and now another build has been certified, this time with version number 14.4.B.0.20. So we’ve now moved from a build template of 14.3.X.X.XXX to 14.4.X.X.XX.
Xperia Z1s owners have been waiting patiently for KitKat to arrive , if Sony/T-Mobile do manage to get this out, it looks like it will be the KitKat update. We’ll let you know if/when the update starts to roll.