Slices of Pie are reaching more and more devices. Ever since Android's latest version was released for Google's line-up, other companies like HMD, Samsung, Sony, Xiaomi, and OnePlus have joined in on the fun. Another OEM, Asus, started its Pie rollout with the Zenfone 5 earlier this month, and is now following up with the higher-end 5Z.
Although a Pie update for the 5Z began making the rounds a few months ago, it seems to have been a limited release for select devices or locales. Now the official OTA is being sent to users, though as these things usually go, it's probably happening in batches so you'll need to be patient before you get it.
The update pushes the build number up to 18.104.22.168 and includes the December security patch. It should weigh well over 1GB, so make sure you're on an unlimited connection before you start downloading it. And if you're too eager to try it and know what you're doing, you can grab the download manually from the source links below. Just make sure your phone has the same SKU model (WW or RU) before you do so.