Galaxystuffs provides the magnificent news about Official CM13 ROM For Oneplus One.
Before starting let me do share more things about this rom as we know it is in beta stage as a result there are some broken stuffs and bugs in it.I can't share the bugs here as it keeps on changing time to time so for bugs report I refer you to check out the Oneplus One forum.
1. Oneplus One with Unlocked boot loader & Custom Recovery Installed(TWRP recovery)
2. After above steps Make backup of current rom your recovery.
#How to Install/Flash Official CM13 ROM On OnePlus One-
Step By Step Guide
1 . Download official CM 13
Download Gapps 6.0 package Copy it in your in your device.
2. Now place the official Cyanogenmod 13 rom and gapps 6.0 zip file in sd card.
3 .Now reboot to custom Recovery mode.
4. Then flash CM13 rom and Gapps 6.0 from recovery in it.
5 .Now Clear cache and Clear Data.
6. Reboot your device.Done! you just flash official cyanogenmod 13 rom in your Oneplus One.
Enjoy Android Marshmallow 6.0 !.