This is because Essential has launched the beta program for the Oreo update, and the best part is that this beta program is open to all. This means that all you’ll need to do is sign up to be part of it and you should be able to start testing out the update on your phone already. Of course given that this is a beta build, it also means that you should expect the various kinks and bugs that typically accompany beta builds.
Whether or not you should be using this as your daily driver is entirely up to you, but it will also depend on whether or not the update will break the functionality of existing apps, so it could be a case-to-case basis. Essential has yet to confirm when exactly the update will be ready, but presumably with the beta program being open to all Essential Phone owners, the company must be pretty confident (to a certain extent) about the stability of the build, which hopefully indicates that a release isn’t too far off.