Samsung is a slightly slower than other companies in giving the latest OS updates to its users, the stable Android 9 Pie will be rolling out for Galaxy S9 and S9+ and it will be earlier than what we have anticipated. It will be rolling out early January 15.
While Galaxy S8 will be pushing the update in Feb 2019. The OS is still in the testing stage and it can change later according to testing. You will get the OTA Android Pie 9, at least in Turkey and a few of other regions.