Level 6+ Local Guides can apply to preview new Google Maps features before they go public.
Google's Local Guides program for Google Maps has proven to be quite successful, with tons of people offering additional feedback and providing photos about various destinations. Part of this is due to the rewards that Google gives to Local Guides; The latest reward is kind of a double whammy for Google - an opportunity to preview new Google Maps features before the public does.
"A secret app for top Local Guides" . The threshold to qualify as a "top" Local Guide is Level 6 (I'm a Level 6 with 2600 points, for what it's worth). The application entailed telling Google what kind of device I have (options included Android, iOS, and "other"), and nothing else. The link to the application is here, but I must caution you that you won't be able to apply at all if you're not a Level 6 Guide.
Link: https://maps.google.com/localguides/home/beta-opt-in
2022
