Xiaomi Mi A1 is the first stock Android smartphone from Xiaomi, its runs completely stock Android. Xiaomi already confirmed that Mi A1 will receive Android 8.0 before the end of 2017, as promised Xiaomi released Android 8.0 Oreo to Mi Al. It was confirmed by Xiaomi on its official twitter account.
Here the device should be in the latest update (with December security patch) to receive the update. To check for the update head to settings-> About device-> software update. Update will be rolled out in phases, it will take couple of days to receive the update.