A few weeks ago Chainfire released a root method for Android 6.0 Marshmallow. The only downfall to the method is that it requires you to flash a modified boot image. Chainfire has now released a new root method for Marshmallow on Nexus devices that does not require you to flash a modified boot image! This is experimental and Chainfire adds to the top of the thread "Do you really want this?". He has a full explanation of the process at the link below. You can also find all files needed and the full method there!
via XDA