Xiaomi released MIUI 9 Global Stable update for its Mi MIX 2 smartphone last month. Today it has announced Android Oreo beta program for the phone, but it is for the MIUI 9 China ROM on its global forum, however it is applicable for all regions. To be eligible, you must be using MIUI China Alpha ROM and must be active on the forum.
Xiaomi started Android Oreo beta testing for Mi A1 last week, so it will likely be the first phone to get the stable update, which is expected in the coming weeks. We can also expect Xiaomi to open Android Oreo beta testing for more phones soon.
You can check out the procedure on how to apply from the source link below. Deadline for the application is December 24th and the eligible members will be selected by December 27th. Since this is Alpha testing, it might take weeks for the stable ROM. Global Android Oreo program is expected to begin in coming weeks.