Xiaomi launched its first Android One smartphone with Mi A1 in India and other parts of the world in Sept. Today, Xiaomi Mi A1 is getting a new update which is 456 MB in some cases and few of them it is almost 1GB as per screenshots shared by XDA developers.
There is no mention of what is this update all about but they have mentioned Nov month security patch as it is Android One device so Google will push security patches soon.Sorry, it is not an Android Oreo update.
This update might fix some of the issues on the device and improve the performance.