Android 10 will be last major OS update for the Asus ZenFone 5Z, but possibility of ZenUI 7 is not being ruled out
The Asus ZenFone 5Z started receiving the Android 10 update last November, and it may very well be the final major OS update for the Snapdragon 845-powered smartphone. An email sent by a ZenTalk forum moderator to a ZenFone 5 user mentions,
Android 10 was the last big FW update for ZF5 but we will continue updating bugs and security updates a while longer. Don't know the end date [sic]."
Though forum responses cannot be always taken as the official word from the OEM, it still makes sense in this case. Most devices offer up to two major OS releases after launch. The ZenFone 5Z launched with Android 8 Oreo and subsequently got updated to Android 9 Pie and now, to Android 10. Therefore, further updates to Android 11 and beyond is a distant possibility and are unlikely to happen.
That being said, the ZenFone 5Z runs on Asus's ZenUI custom skin over the base Android OS, which means a lot of features can still be backported from a future Android OS update to ZenUI in a similar manner as to how Xiaomi updates MIUI with new features while still being on an older base OS.
We can always hope but do have in mind that Samsung sold millions of those phones and their cost to release a new Android is about the same as for us. I'm not saying that it won't happen but don't get surprised if it doesn't."
Looking at the moderator's reply, it is very possible that the ZenFone 5/5Z has reached the end of the road when it comes to major updates save for monthly security patches and minor optimizations. That being said, an increasing number of custom ROMs are being made available for the ZenFone 5Z, so all is not lost if you don't mind dabbling with unlocking the bootloader and installing third-party ROMs.