Xiaomi has started to roll out the Android 8.0 Oreo-based MIUI Beta update for the Xiaomi Mi 6. This is for the global variant of the device and the build number is version 8.1.11.
You will need to be on a previous MIUI 9 beta ROM(7.12.14) to receive the Oreo beta as an OTA download. Xiaomi is also looking for new beta testers for the Oreo ROM, so if you’re interested you can sign up over here.
The Oreo Beta update includes some new features as well as improvements and bug fixes.