The HTC One M9 has had an unofficial build of CyanogenMod 12.1 for a few weeks now, but a few major features just are not working since developers have not had access to Kernel source for the device. The camera force closes and there were a few other big bugs. Now that developers will have access to the 5.1 kernel source they will be able to start squashing bugs. Who knows we may end up with an official build CyanogenMod 12.1 from CM. This is pretty big for development. Other rom developers will be able to use CM as a base to bring us many more roms.
via HTC Developer Center