CyanogenMod has officially released CyanogenMod 13 nightly build (CM13) for a range of devices, which includes OnePlus One, Moto X 2014, LG G3, LG G4 and Nexus 7. Based on the Android 6.0 Marshmallow, CM 13 updates bring a number of useful additions to marshmallow, like the theme engine to enhance your Android experience.
Currently, official CyanogenMod 13 nightly builds (Android 6.0 Marshmallow) are available on OnePlus One (bacon), Nexus 7 (deb & flo), LG G4 (h815), Galaxy Tab Pro 8.4 (mondrianwifi), LG GPad 7.0 (v400 & v410), LG G3 Verizon (vs985) and Moto X 2014 (victara). Other devices are imminent.
One of the advantages of CM 13 is that it updates many devices to the newer version of Android before the manufacturer has officially made available. Also, while the ROM combines a near stock look and feel, it enables users to customize their devices completely.
Official CyanogenMod 13 Nightly builds are now available for download [HERE]. If you are on CM 21.1 nightly, you can dirty flash CM 13 nightly on your device. If you use Xposed, Open Gapps, etc. flash a Marshmallow compatible after installing CM 13.
It is advised that CM 12.1 snapshot (stable build) users wait for the CM 13 snapshot, which may release in Jan 2016. (Source – CM)