The Android 8.0 Oreo update rollout seems to have started for the Samsung Galaxy A3 (2017). The update currently rolling in Russia for the Galaxy A3 (2017). Russia is also the first country where Galaxy A5 (2017) received Android 8.0 Oreo update. The build version of the update is A320FXXU3CRD4.
The Galaxy A7 2017 and Galaxy S7 were also cleared by the Wi-Fi Alliance alongside the Galaxy A5 2017 and A3 2017, we expect them to start receiving Oreo very soon.
The update seems to bring April 2018 security patch with Android 8.0 Oreo. It brings the same feature as Galaxy A5 (2015). If you have Samsung Galaxy A3 (2017), you can check for the update by going into the Setting > Software update.