https://wccftech.com/stable-android-oreo-update-for-samsung-galaxy-s8-leaked/

Samsung began accepting applications for beta testers for Android Oreo sometime last November.  According to a statement by Samsung, the beta should officially end on January 15th. The official OTA update was expected to roll out sometime in March, but a non-beta, stable version has been leaked online, on Reddit.

The leak, however, is only for Galaxy S8 devices running the Qualcomm Snapdragon 835 SoC, which is at the moment is available in US and China alone, so users outside of those two countries have to wait a bit longer. The update has to be manually installed via ADB sideload, so we recommend that you read up on it before attempting to install it, as improper installation may hamper the functionality of your device.