Cyanogenmod itself is a custom ROM that comes as the default firmware in the device.
Oneplus officially just announced astock android rom.
It does require you to unlock your bootloader and install a custom recovery to flash.
If somebody needs an AOSP ROM on your OnePlus One just to try out then this one is for you for sure.
Flashing this does not void your warranty unless you screw up and brick the phone.
WARNING:
Please visit the ROM disclaimer link before you proceed to flash this.
Understand that I am not at all responsible for your broken device.
ROM disclaimer link.
Please visit the ROM disclaimer link before you proceed to flash this.
Understand that I am not at all responsible for your broken device.
ROM disclaimer link.
Pre-requisites for this installation:
- AOSP ROM for OnePlus One
- Google Apps
- Unlocked bootloader and a Custom recovery
Installing AOSP ROM on OnePlus One:
STEP 1:
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Copy the ROM package on your phone's SD card.
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STEP 2:
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Boot into recovery.
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STEP 3:
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Flash the ROM zip package using the custom recovery
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STEP 4:
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Reboot your phone and check out the AOSP ROM
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Source: Xda-Developers