Asus Zenfone 5z was announced back in June 2018 running Android Oreo. Asus has now started to roll out Android Pie to all Zenfone 5Z models. The update carries version number WW_user_18.104.22.168_20190117 and weighs around 1GB. The update does not provide any other details about the update and we expect the update brings the latest security patch as well.
The update will be rolled out in phases and it will take some time for the update to hit all the devices. The update is also not available for download on the Asus website to flash manually.