For your information, Xiaomi has already rolled out stable Android 8.0 Oreo to Mi A1 with features like Picture-in-Picture mode, Adaptive icons, Notification Dots, Autofill Framework, Smart Text Selection, Instant Apps, quick boot, Background limits and much more. However, the company continually rolling out new beta builds with improvements.

The current beta build OPR1.170623.026.8.2.6 starts rolling out through OTA (over-the-air) for devices runs on software build OPR1.170623.026. 8.2.1. Other users can download the full ROM and flash manually via Mi Flash tool. However, first you need to unlock the bootloader of the device (read this guide). The below guide requires ADB and Fastboot driver setup on your computer. Also, ensure at least 50% battery charge remaining on the phone.

How to install Android Oreo Beta on Mi A1 Manually

  1. Download Mi A1 Oreo Beta (build OPR1.170623.026.8.2.6) from here.
  2. Unzip the downloaded file (use 7zip)
  3. Boot your phone into fastboot mode (hold Volume Down + Power button after switching off the phone).
  4. In the ROM extracted folder, execute Rom-Flasher.bat file.
  5. Select any of the 3 options to install the Oreo beta build. Note that option 2 will avoid conflicts, but data will be erased. (Source)