Samsung is sending a new software update for the Galaxy S8, S8+, and the Galaxy Note 9. The latest update includes the May 2019 security patch along with minor bug fixes and performance improvements. This update is currently rolling in Europe but will soon reach to other users globally.
The software versions are:
Galaxy Note 9: N960FXXS2CSDJ
Galaxy S8: G950FXXS4DSE1
Galaxy S8+: G955FXXS4DSE1
If you want to check for the update manually you can do this by heading into the Settings > Software updates.