With the beta program now completed, members of the Android Beta Program are now starting to receive the production build of Oreo 8.1. Google released this final build yesterday and those with with Pixel devices and Nexus devices that were in the program should start seeing the OTA update to the production build over the next few days.
The update is very small, just over 40MB, reflecting the fact that the second and final beta of Oreo 8.1 was all-but complete. That small of an update means very few bugs were found to be fixed.
If you are new to the Android Beta Program, there is nothing special you need to do. The OTA will download to your phone just like any other update from Google. It is just a matter of when it gets to your account.