Xiaomi's flagship, the Mi 6, is getting an update to Android 8.0 (Oreo) as part of the MIUI 9 Global Beta Test, which also includes a new Android 7.0 (Nougat) based ROM for the Redmi 5A family and the Redmi Y1 family, and the company is actively seeking testers. Interested parties can apply on the company's forum via the source link. In order to meet the minimum qualifications for a beta tester, all you have to do is own the device in question and be an active participant in Xiaomi's forums. It's worth noting that you cannot apply from a web browser, mobile or desktop; you'll have to download the MIUI Global Forum app. From there, Xiaomi will choose a crop of testers on December 29. Applicants have until December 26 to put in their applications.
This is a worldwide test, open to users in all regions. As such, once you're selected, you cannot ask for a transfer to the China beta testing team. You'll need to own a Xiaomi Mi 6, or a Redmi 5A or 5A Prime, or a Redmi Y1 or Y1 Lite. Testers must be able to communicate both with staff and amongst themselves in English, and must use QQ to communicate in a special beta testing group, along with continuing to be active on the official forum. Obviously, once you're selected, you'll be dropped from the test if you flash any ROM on your device besides the official global beta MIUI 9 ROM from Xiaomi.
Beta testers, as they always have, will receive many of the same privileges on the forum that Xiaomi staff and higher-ranking forum members have. Testers can contact staff directly, post large files, get prizes for good performance, access daily MIUI update builds, and even enjoy priority when participants are being chosen for MIUI-related events and activities. It should go without saying that anybody who's on a specialized team in the forums, such as bug hunters, designers, administrators, and photographers don't need to apply for the Beta test, and can simply flash an updated MIUI Global Beta build to their device of choice if they wish to participate in the beta.