Samsung won’t comment on firmware update releases @asif
The advice is to periodically check your phone software update section.
Oreo is only just been released on Beta for s8 and s8+ handsets and those that signed up to the Beta Programme, so until the Beta Programme has ended it wouldn’t be released generally. I’d expect Oreo on my s8 mid 2018.
If your phone was supplied by a Network then that Network controls the release of the firmware which is usually after they’ve tested it to ensure it doesn’t clash with their network and features. That said Networks can also take the standpoint of not giving timeframes.