HAMR is a new recording systems that uses CMR but with lasers to heat the surface to achieve higher density. Heating the surface allows a better magnetic recording and allows the reduction of the track sizes resulting in higher recording densities.
You can now buy drives with 32TiB of data storage, which is approximately 29TB in the proper way of describing storage. How reliable? Well the manufacturers believe so and willing to risk destroying the data centre and NAS market if they get it wrong. Guess the drive dies when the laser dies, but they are still quoting the 2.5 million hours for MTBF (2 centuries)
Mozaic is Seagates implementation of HAMR
EDIT: Not as new as I first thought, I even have a HAMR drive (24TB) bought a couple years ago.
EDIT2: pulled the drive out of the NAS to check for the laser marking on the case and its not there. Seems only the new 24TB drives are HAMR