Google has announced the official rollout of Android 6.0 Marshmallow, and from the 5th of October, supported Nexus devices will begin to receive the update to this latest version of Android. Specifically, the Nexus and Nexus 6 phones, as well as the Nexus 7 (2013) and Nexus 9 tablets qualify for this update. Android One devices will also start getting the update.
At the same time, Google will be pushing the Android 6.0 source to the Android Open Source Project (AOSP), so manufacturers can start working on updates for their smartphones and tablets. Different manufacturers are at different stages of confirming which of their existing smartphones will get updated to Marshmallow.