Xiaomi launched the new iteration of its skin, MIUI 10, a short while ago. While most devices will receive the skin update, it doesn't guarantee an OS update to Oreo.
https://www.notebookcheck.net/Xiaomi-OS-update-roadmap-revealed-Redmi-Note-4-to-remain-on-Nougat.309146.0.html
I wonder what's the excuse for not updating some 7.x phones to 8.x or 9.x Android.
There is literally no HW reason why a phone that has the capability of running 7.x can't run 8 or 9, since HW specs haven't gone up.
It's just sad how they don't even try to hide that it's a case of deliberate obsolescence.