If you own Xiaomi Mi 5 and want to upgrade to Android 8.0 Oreo right now with MIUI 9 Global Beta ROM, then here is how it is. Note that, Xiaomi recently rolled out MIUI 9 Global Beta ROM 8.3.1 for Mi 5, but the incremental OTA update is still based on Android 7.0 Nougat. To get Android Oreo, users need to install the Oreo based MIUI 9 Global Beta ROM 8.3.1.
The manual installation process requires some technical skill, so inexperienced users are recommended to wait for the Oreo OTA update, which will roll out soon. There is a good news for custom ROM fans. The LineageOS team has released Android 8.1 Oreo based LineageOS 15.1 for Xiaomi Mi 5 (code named Gemini). If your device running on a custom ROM, then you can flash the official LineageOS build and enjoy great features. Details available in this post. Comes to Oreo based MIUI 9 Global Beta ROM. You can download and install the ROM (recover/fastboot) right now. Here is the download link and installation instruction. Download & Installation: Download MIUI 9 Global Beta 8.3.1 Oreo Recovery ROM for Mi 5 (code named Gemini) from here and Fastboot ROM from here. After downloading the firmware, follow this detailed installation instruction. Note: Since this is the major Android upgrade users are recommending to do a clean Fastboot install, even if their device is running on MIUI 9 Global Beta ROM. (source)
