I am on the latest AS version (3.1) with gradle plugin 4.4. I've been getting the same error as stated in this SO issue https://stackoverflow.com/questions/49512629/android-studio-error-default-interface-methods-are-only-supported-starting-with While the solution seems to work, and there is an explanation to what might be the cause of the problem, I do not know the full extent of the problem and what this fix does. Is anybody else getting this as well? Anybody using Google's Architecture Component should be running into this same issue as well.