The update is about 1.1GB in size and it also comes with a newer June Android security patch. At the time of writing, it isn’t available for Malaysian users yet but there are reports that it’s already available in India and the Philippines. You can check manually on your Mi A1 by going to Settings > About Phone > System Updates.
Android 8.1 is a minor incremental upgrade over Android 8.0. You get the ability to view battery level of your connected Bluetooth devices as well as a notification sound limiter. This restricts apps like Facebook Messenger from buzzing your device non-stop if you didn’t switch on a phone after a long time.
According to XDA Developers, there’s a potential bug with the update where your entire SMS history may be erased. It isn’t clear if Xiaomi would suspend the update roll out to fix this bug. If you do get the Android 8.1 update notification, it is advisable to backup your SMS first if it matters to you.