Sony updated Xperia Z1 and Xperia Z Ultra to Android 4.3 back in December. But, the firmware has now received a bug-fix update with build number 14.2.A.1.136, to fix a handful of issues with Wi-Fi performance, Bluetooth music streaming and e-mail, while adding a new white balance setting for the display.
The new 14.2.A.1.136 stock firmware build is part of Sony's maintenance update which is only accessible via Sony's PC Companion and Mac Bridge apps. The Over-The-Air (OTA) update is still inaccessible for both the devices, as Sony is rolling out the new update in phases.
The Android 4.3 bug-fix rollout was announced for Sony Xperia Z1 and Xperia Z Ultra via Twitter recently.
Here is what Sony announced in its recent Twitter update citing a handful of improvements:
It must be noted that the update will be released via OTA in phases. So, those who are unable to access the new update via OTA update notification or other sources, can try forcing the OTA download manually by going to Settings > About Phone> System update and tapping on Check for updates.