After HTC, Samsung and LG, Sony began deploying Android 4.4 KitKat to its mobile phones. Some users residing in Hong Kong were offered the update over-the-air on their Xperia Z Ultra. The news was reported on the XDA forum. For now, it seems that Sony does not yet offer the firmware via PC Companion.
Hopefully the manufacturer will soon extend the deployment to other regions and also to other devices.