Google has been quite pragmatic about their Glass program, especially as it relates to development. At Google I/O this year, developers were told a Glass Development Kit (GDK) would be coming to fruition soon, and available for them to start work on apps for the Glass interface.
It’s been a few months since I/O, and developers continue to go wanting for the GDK they were promised. Rather than commit to a timeframe for when it would be available, Google is instead asking developers interested in Glass to develop for Android.
Asking developers to use API level 15, which pertains to Android 4.0.3, Google is still “hard at work” on the GDK. Glass is running Android 4.0.3, so it makes a bit of sense that developers would familiarize themselves with that particular API.
This leads us to believe that the GDK is very similar to the Android SDK as “some features that you want in the GDK are already supported by the Android SDK”, and that the GDK is nowhere near ready for release. According to the Google+ post, “Although you won’t have all the tools necessary to design the perfect experience for Glass, developing with the Android SDK (API Level 15) lets you try out ideas while you wait for the GDK.”
The team behind Google Glass development has released a few APK samples to get everyone on the right track, and notes that “When we release the GDK, we’ll update these samples to demonstrate the migration path between a traditional Android app and a full Glass experience.”