The previous reply is a little bit outdated (10 years), so here's an updated information:
See here for early access release:
Playstore : How to release early access app?
and here is the direct information from Google:
https://developers.google.com/assistant/console/releases?hl=en
Basically you have these options:
- Draft
- Close testing (Alpha) - only users who knows about the app, no review required
- Open testing (Beta) - early access, requires review
- Production - before review
- Released/To-be-fixed - after review
Here is the scheme from the Google page:
