Android M will now officially be known as Android 6.0 Marshmallow.
Google revealed the next version with the unveiling of a new Android statue in front of the iconic Building 43 at their Mountain View campus. Some people were speculating that Android M might have been called Android 6.0 Milkshake, as indicated by the watch face that was on the watch that Google’s VP of Engineering, David Burke was wearing back at Google I/O 2015.

But that just turned out to be Google trolling us and getting us speculating about this year’s desert name.
In years past, a new version of Android has always launched with a new piece of hardware (more commonly a Nexus phone) to launch alongside it.
Google hasn’t said when Android 6.0 Marshmallow will launch but typically both the new version of Android and Nexus devices launch between September and November of each year.
Google has also released the SDK for Android 6.0 so then developers can start to make their apps compatible with the new version. Also if you have a Nexus 5, 6, 9 or the Nexus Player, you can install the 3rd developer preview of Android M (now called Marshmallow).
We might see two Nexus phones this year. One will be made by LG which will be like an updated Nexus 5 (below is what it is rumoured to look like), which a lot of people loved when it first came out in 2013. The other Nexus phone we might see is one made by Huawei and will be closer in size to last year’s Nexus 6 at 5.7-inches.

Now all we have to do is just wait a bit longer.
Source: Google