Google is now reportedly expanding the Maps Go beta to all users globally, as indications of the app in beta form have started appearing for users in the Middle East, the UK, Europe and other regions. Prior to this expansion the app was only available to users in the U.S. and a very small collection of other regions, but now Google seems keen on pushing it out for everyone to give it a try and you aren't necessarily required to have an Android Go phone to give the app a shot.
There isn't a comprehensive list of locations where the beta for Maps Go is now accepting users into the testing period, so if you reside in a region or country where it wasn't available before today or the last few days, then the best way to find out if you're able to enter the beta now is to simply head to the Play Store and see if it's available for installation. That said, Google Maps Go is a form of the full-fledged app that aims to help keep things running smoothly for users who run Android on a device that doesn't exactly have a lot of RAM to begin with, so if you're using a top-of-the-line smartphone like the Galaxy Note 8, Galaxy S8, Galaxy S8 Plus, or any of the Google Pixel devices or any number of other high-end flagships, then you really don't have a need for this particular app beyond wanting to see the differences in how it runs on your device compared to the normal version of Maps.
Another thing to pay attention to is that to help cut down on the size of the APK for Maps to help devices with less RAM as well as help them run the app in an optimized state, Maps Go does cut some features out of the mix that you'll still find in the full version of Maps, so if you want the full experience Google intended, then you'll want to stick with the standard version. Maps Go is the latest of Google's applications to roll out to more users alongside other offerings like YouTube Go.