Apart from the ZenFone 4, the rest of the ZenFone line up including the bigger ZenFone 5 and ZenFone 6 will be receiving the latest Android 4.4.2 KitKat update very soon. ASUS Taiwan has announced this on their forum and it will bring a host of improvements and bug fixes.
The update is currently being rolled out in Taiwan and China, and it should be arriving on our shores very soon. It is recommended to use WiFi connection to download as the update is about 450MB in size. To find out if it is available, head over to Settings > About > System Update > “Check Update”.