As you can see, it is official cm12.1 and i am just a person who maintains this thread.
The following people are maintainers for this device : @epinter
The following people and/or organizations have contributed to this device: @Hashcode0f, @dhacker29, @Skrilax_CZ, @kabaldan
/* * ~ Please READ ME ~ * * I do not guarantee any successful flashing. I am not responsible * for bricked devices, dead SD cards, or a broken device. YOU are * choosing to make these modifications, and if you point the finger * at me for messing up your device, I will laugh at you. But I will try * my best to explain all the necessities, so you won't mess up your Device. * * ~ END OF AGREEMENT ~ */
! Download the zip file
! Make sure you have atleast 50% battery left
! Make sure you have backed up your current rom
! factory reset your device, erase delvik cache and format /system (if you are using philz recovery, use clean to install new rom)
! flash the ROM zip, GApps zip
! reboot device
! First boot takes around 10 - 15 minutes. Its normal.
For More details, please visit Cyanogen wiki page of Atrix HD
Download cm12.1 from here
Download GApps from here
Click here for changelog