The folks at CyanogenMod work fast. It was only two days ago that the AOSP code was updated with October's security fixes (following Google's promise to issue monthly security updates to Android) and now these changes have been merged into the custom ROM's code and are stable enough to deserve a "snapshot" label instead of the nightly status.
This isn't the first 12.1 stable(ish) release from CyanogenMod. The title goes to last month's snapshot which brought Android 5.1.1 to many of CM's supported devices. But this new build should be even more stable and reliable than that thanks to the new fixes. It isn't yet available for all devices, but the list includes the likes of the Nexus 4, Nexus 7 2013, Nexus 9, HTC One M7, and more. Check it out and if your device isn't there yet, it might be coming as soon as the maintainers are ready to mark it as "good to go."
CyanogenMod also noted that it's assessing the source code for Marshmallow and will have more details regarding its plans with Android's new version later.