Shortly after the announcement of iOS 8 in 2014, Google made headlines by saying that it would make full-device encryption mandatory for new Android devices running version 5.0. It then made more headlines several months later when we discovered that the company backed down, “strongly recommending” that Android device makers enable encryption but stopping short of actually requiring it.
Now Google has published an updated version of the Android Compatibility Definition Document (PDF) for Android 6.0, and it looks like mandatory encryption is back with a couple of exceptions. New devices that come with Marshmallow and have AES crypto performance above 50MiB-per-second need to support encryption of the private user data partition (/data) and the public data partition (/sdcard).
The relevant portion of the document, emphasis ours: