CyanogenMod must be getting ready to move on to Android Marshmallow. They just released a Stable build of CyanogenMod 12.1 bringing the stable Android version to 5.1.1. When CM says stable it means that an actual person checked the build. CyanogenMod is known for their self compiling robots that release updates nightly. Most of these updates are incredibly minute and sometimes amount to nothing. Other times the nightlies fix one thing to break another.
Everything that CyangeMod puts out you can assume is in Beta unless it is labeled as Stable. This means that there may be some bugs present. The great thing about running a Stable version of CyanogenMod is you really don't have to worry about the bugs. Head to the link below to see if your cell phone is compatible.
via cyanogen