Update [June 18]: Okay, good news! The Pie update for the ZenFone 4 is back online. Asus announced it again here today and confirmed that the update is in the beta stage. In fact, it’s also available for download. See the link at the bottom of the article.
Update [June 17]: Asus pulled the Pie update within hours of announcing it. Yes, that is bad news.
Asus has a new software update for the ZenFone 4 variant with model number ZE554KL. The software is arriving as version 16.0620.1905.10 and brings the much awaited Android 9 Pie OS to the device.
This is the first device in the ZenFone 4 series to receive the stable update to Pie, the second and last major OS upgrade for the 2017 devices that came preinstalled with Android Nougat. In May, Asus started testing Pie beta on the ZenFone 4 Selfie (ZB553KL and ZD553KL) and ZenFone 4 Max (ZC554KL).
The rollout started today and also includes an updated Android security patch, but being an OTA update, it will take time before all units receive the download notification. You can check if the OS is available for your device in Settings > System > System updates and download manually.
Related: Asus ZenFone 4 software update news