Jason Eason, Product Manager at Android, announced this over on the android developers blog with the release of the Android 6.0 SDK.
Google Android MarshMellow
The new Operating System will come with a host of improvements, including better battery life, faster transitions and executions, as well as the introduction of Google's new mobile payment platform.
The official release date is yet to be revealed. After last year's somewhat 'buggy' release of the Lollipop Operating System, Google are probably going to take extra care with the roll out of Marshmallow.
Google has always found inspiration from sugary treats when naming the Android Operating systems.
As mentioned above, Lollipop is the name of the current Android Operating system, with KitKat being Lollipop's predecessor.