The new official ROM is based on the Android 5.1.1 (Lollipop), which is designed to increase performance and reliability over stock Android for your device. CM12.1 is one of the most famous ROM and comes with lots of features and customizations. Without wasting much time outlining the features of this rom, lets begin.
To get started, you will be needing a custom recovery to flash two zip file on your phone. Before following this tutorial do take full backup of your Xiaomi phone and save the backup file in some safe place. Read all the steps carefully and follow them one by one on your Xiaomi Mi4 and Mi3 phone.
GUIDE TO INSTALL CYANOGENMOD 12.1 ON XIAOMI MI4 AND MI3
Step 1. First of all, download the TWRP recovery here to your phone and Go to Setting>Updater or Open Updater App from home screen. From here Press menu button and then “Select update package”. Select the recovery zip and install it. Reboot device. If you already done this then proceed.
Step 2. Download the CM 12.1 ROM for Mi 3 and Mi4 here and save it on your desktop. Don’t extract the folder on your desktop.
Step 3. Now download Google Apps package zip file here (IMPORTANT) and save the zip file on your desktop.
Step 4. Now move both the downloaded file to your phone and remember the location of the files.
Step 5. Reboot your phone into TWRP recovery mode (Go to Tools > Updater > press Menu key and select ‘Reboot to Recovery mode’)
Step 6. Now from the recovery menu, Select ‘Wipe’ > Advanced > select Wipe data & cache and confirm.
Step 7. Go back and select "Install". Select the CM 12.1 ROM File and Flash it.
Step 8. Once the flashing process is done again select the Google apps package and flash.
Step 9. Now go back and Reboot your phone by selecting ‘reboot system now’.
That’s it! Now your MI 3 and Mi 4 phone is running on the CyanogenMod 12.1 Android 5.1.1 ROM.