While Nexus and Google Play Edition devices are receiving Android 4.4 KitKat updates, OEM-skinned devices always take too long to receive these updates. Though the Xperia Z (C6603) and Xperia ZL (C6503) will receive the Android 4.4 update in 2014, a leaked version of the Android 4.3 update meant for these devices has been posted online in the form of an ftf file which can be easily flashed via FlashTool.
The build number for both the leaks is 10.4.B.0.569 and the firmware has been tested by users on XDA forums. Most users have reported a significant increase in the device’s performance without any bugs. Since this is an unofficial leak, there is a possibility that the official version that will be rolled out Over The Air (OTA) might carry a different build number.
It is important to note that flashing this on your device will not void the warranty as it is a Sony-certified firmware. Also, flashing this firmware will revoke root access in case your device is already rooted but it will not affect the bootloader status.
To learn how to flash it to your device via FlashTool, you can refer this guide that I posted for the Xperia P.
Should you face any issues while flashing, feel free to leave a comment below and I’ll be glad to help you.
Download links and leaks courtesy of XDA-forum member Androxyde.