CyanogenMod 12.1 is now officially available for the OnePlus One. So if your Phone does not shows up an OTA update here is how you can get it
What is new in CM12.1 ?
Smarter Screen: LiveDisplay intelligently adjusts your screen based on environmental conditions.
Calendar Together with Email: Enjoy the latest Boxer powered experience where you can seamlessly share your availability and schedule appointments.
Cyanogen Browser: The new Cyanogen browser delivers search results and loads web sites faster and more securely than leading browsers.
Redesigned Launcher: App Drawer and Folders have been redesigned for one-handed use.
Fresh AudioFX: The user interface has been updated for consistency across all devices.
More Playback support: We’ve substantially increased our support of codecs for video and audio playback.
Read more on Cyanogen blog
update and flash it via recovery mode.
1. Download the OTA equivalent zip file from the below link to your phone (645 MB) or download to your PC and move it to your phone.,
2. Turn off device.
3. Turn on device while holding volume down (select recovery) and press power.
4. Apply update (from device) navigate your way to your download folder and select the zip file and apply. To navigate use volume up and down and select with power.
5. When the updates done go back and wipe cache.
6. Reboot and enjoy.
Read more here (Do it at your own risk).
I upgraded my device from COS12-YNG1TAS2I3 to the new CM 12.1 – YOG4PAS1N0 with out any issues