https://www.anandtech.com/show/12169/seagates-multi-actuator-technology-to-double-hdd-performance : "Seagate says that the Multi-Actuator Technology is to be deployed on products in the near future, but does not disclose when exactly. As the company's blog post on the matter mentions both MAT and HAMR, it is highly likely that commercial hard drives featuring HAMR due in late 2019 will also have two actuators on a single pivot. At the same time, it does not mean that the MAT is not going to find itself a place in products using conventional PMR."
US patent 2915594, Burns Jr., Leslie L. & Keizer, Eugene O., "Magnetic Recording System", published 1959-12-01, assigned to Radio Corporation of America
Seagate statement 4 December 2018: "The Exos HAMR drives run like all other drives in a standard suite of integration benchmarks. At this point in early testing, they're meeting our expectations for how a drive should interact in each benchmark".