https://www.techradar.com/news/essential-phone-receives-long-awaited-android-oreo-81-update

After numerous beta updates and delays, Android Oreo has finally landed on the Essential Phone. Originally intended to launch with the vanilla version of Oreo, Essential opted instead for the latest version due to some stability concerns.

If you check for a software update, you should have immediate access to the overdue upgrade, which will require a restart once the download is complete.