We're currently on the fifth generation of ASUS ZenFone devices, but that doesn't mean that previous models have been (entirely) forgotten. The ZenFone 4 Max has just begun receiving its update to Android 8.1 Oreo, which also includes ASUS's ZenUI 5.0 skin. This is a few months behind schedule, but at least it's here now.
This update carries version number 15.2016.1809.412. There are two release notes, and they don't tell us much:
Update OS to Android 8.1.0 Oreo.
Update ASUS ZenUI to 5.0.
So if you have a ZC554KL model of the ZenFone 4 Max, keep an eye out for an 8.1 Oreo OTA. ASUS notes that OTAs are sent out in batches, so you might have to wait a couple of days to receive the update.