OnePlus One, which is currently running on the CyanogenMod 11S (Android 4.4 KitKat) ROM will receive the CyanogenMod 12S (Android 5.0.2 Lollipop) OTA update shortly. However, an unofficial build of CyanogenMod 12.1 (Android 5.1) is now available for OnePlus One. Interested users can update their OnePlus One to Android 5.1 with CM 12.1(Unofficial) custom ROM.
The new CyanogenMod 12.1 (Android 5.1 Lollipop) custom ROM (unofficial) for OnePlus One brings some of the key features of the new Android 5.1 OS, including the revamped Material Design user interface, animations and graphics. Besides, it will enhance the phone’s performance and extend the battery life.
The following guide shows you how to install unofficial CyanogenMod 12.1 (Android 5.1 Lollipop) custom ROM on OnePlus One. However, please note that this is an experimental build. It might have many bugs that have not been fixed yet. According to the developer, the major bugs on this ROM are: When open “Select and order tiles” settings force close, when installing apk with file manager, package installer crashes, but App will be installed, when receive SMS, SMS app force close, alarm function force close.
Disclaimer: Please follow this guide at your own risk. Though we are putting our level best to provide this tutorial at its maximum perfection and accuracy, we can’t take responsibility for anything that goes wrong. This guide is intended for technically talented users only.
Important: As always, create a backup of all important data in your OnePlus One. Also, make a Nandroid back up of your device from recovery.
Note: This is a nightly build, which means it will contain many bugs.
1. Connect your phone to your computer and transfer the downloaded CM 12.1 ROM zip file and Gapps zip file to the phone.
2. Disconnect your OnePlus One from computer, then power off it and then boot it into Recovery mode by holding the Volume Down and Power buttons.
3. From recovery, make a Nandroid backup. Next, wipe the cache and the dalvik cache.
4. Now, go to “Install zip” option and then “Select zip”. Choose the CM 12.1 ROM zip file.
5. Once the process completed, once again, go to “Install zip” option and then “Select zip”. Choose the Gapps zip file.
6. Now, again wipe dalvik cache and then select wipe data/factory reset. After the process is complete, reboot the phone.
Note that the first boot will take a few minutes. Do not press any button until your phone boots up (source – XDA).