Xiaomi has announced the release of MIUI 9.5 ROM for its Mi 8 and 8 SE smartphones. Specifically, it's the China Stable V9.5 ROM that we are talking about here. Post update, the MIUI version of your Mi 8 and 8 SE units should be V9.5.6.0 (OEACNFA) and V9.5.6.0 (OEBCNFA), respectively.

As far as MIUI 10 is concerned, it's still not available. Although it was supposed to be released this month, turns out it won't be coming until next month at least. Here's what a member of MIUI device team recently said in a post on Mi 8 forum:

MIUI 10 is currently in Beta phase and will be pushed to the stable channel only when the standards for stability and usability are met. It may take around a month or two. Since you are on the stable rom, you can expect an OTA update at any point the coming month, no specific dates are available right now. IF you are eager to test out MIUI 10 feel free to switch to beta channel, but stability might get sacrificed in the process.

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