Google says that the GoogleCloudMessaging object is required for upstream messaging, which I believe is part of Google Play services. Glass does not have Google Play Services and has been opened as an issue to Google.
I've gotten downstream messaging to work on Glass using an older GCM API with the help of this post, however none of the questions I've seen (1, 2, 3) address upstream messaging. I was able to use the older GCM API as it did not require Google Play Services but unfortunately it doesn't support upstream messaging.
Can anyone please help me somehow implement upstream messaging on Glass? Perhaps there is a way to add Google Play Services to Glass?
Thanks