Android Marshmallow was initially announced at Google I/O on May 28, when it was released as the Android M developer preview. Several updates to the preview came out before Marshmallow was officially named on August 17. Google finally unveiled Android 6.0 Marshmallow, alongside the 2015 Nexus devices, on September 29, 2015.
As usual, Google's Nexus family was first to get the goods, and the brand new and were the launch devices for Android 6.0. Factory images for most of the existing Nexus range – the Nexus 5, Nexus 6, Nexus 9 and Nexus Player – appeared on October 5.