The Cyanogen team has resumed Cyanogen OS 12 OTA rollout for OnePlus One, which was withheld due to the missing Ok OnePlus feature. The latest OTA, which bumps the build version of the phone to YNG1TAS17L adds a number of fixes along with the voice command functionality.
However, if for some reason you wish to revert to CyanogenMod 11S (CM11S) from Cyanogen OS 12, here is a guide to help you restore the older firmware, for which credit is due to OnePlus forum member pmdsp.
Note that this method will wipe your device and restore the stock CyanogeMod 11S firmware. Create a backup before following the guide. IBTimes UK will not be held liable for any mishap with the device.
How to roll back from Cyanogen OS 12 to CyanogenMod 11S on OnePlus One
Step-1: Download the appropriate stock fastboot ROM file for OnePlus One from here
Step-2: Unzip the downloaded file and keep it on your desktop
Step-3: Boot your OnePlus One into fastboot mode. Disconnect the phone from the computer if it is connected to it and switch off the phone. Hold Volume Up and Power buttons together simultaneously until the fastboot menu appears on your phone's screen
Step-4: Install ADB drivers if you have not done so
Step-5: Download one of the following zip files depending on the storage capacity of the phone
Step-6: Unzip the downloaded file and copy it to the folder where you have kept the stock ROM. Run the file by double clicking on it
Step-7: The script will unlock the bootloader of the phone, before installing the CyanogenMod 11S file. Follow the on-screen instructions
If the phone reboots after unlocking the bootloader then just disconnect the phone from the computer and enter into fastboot mode again
Step-8: The script will do the rest for you and continue installing the CM11S
Note: If you have already unlocked the bootloader of your OnePlus One, there will be no interruption as the script will install the CM11S.
You can now enjoy the CM11S software on your OnePlus One.
Head over to OnePlus forum for help if you have trouble restoring CM11S on OnePlus One.