CyanogenMod 12.1 for Google nexus 4 is based on Android Lollipop 5.1.1. This is an official build and you will be getting daily OTA updates oce you flash this ROM.
CyanogenMod is a free, community built, aftermarket firmware distribution of the latest Android version, which is designed to add some more features, increase performance and reliability over stock Android for your device.
CyanogenMod is primarily based on the Android Open Source Project with extra contributions from many people within the Android community.
Installing custom ROM requires a custom recovery to be installed on your device, which may VOID your warranty and may delete all your data.
Before proceeding further you may consider backup your all data.
Please visit the Disclaimer page below to agree with the risks involved and proceed before flashing this ROM to your phone:
ROM Disclaimer link
Recommended files of CyanogenMod 12.1 for Google nexus 4 installation:
Flashing CyanogenMod 12.1 for Google nexus 4:
Copy the ROM zip and the GApps zip file to your internal memory (By using a USB cable or via adb push command).
Reboot into recovery by pressing key combination or type the following command if you are on a PC:
$ adb reboot recovery
Wipe Data/Factory Reset
Format /system, clean Dalvik Cache (If you are coming from KitKat ROM) and then Format Cache
This step may delete all your data.
Consider backup your data out of your phone.
Data Backup guide
Select the Install Zip from SDcard option.
Select the ROM zip file where you have kept in the SD card and do the same for GApps also.