Leanplum now supports Google's Firebase Cloud Messaging (FCM) for push notifications!
FCM is Google's replacement for Google Cloud Messaging (GCM). While Google is still technically supporting GCM (and you can continue to use GCM with Leanplum), all of Google's new development is focused on Firebase. In fact, all new Android apps must now use Firebase for push notifications.
If you're already sold on Firebase, and want to transition to it from GCM, check out or guide on how to Migrate your app to Firebase Cloud Messaging.
Or, if you're still not sure and want to read up on FCM a bit more first, check out Google's page on Firebase.