It is.
- Classified in the 2xx series
- two power cars working in multiple with a number of intermediate trailers
- coach designations are TS etc (i.e trailer standard) not SO etc
- the prototype unit was originally configured as locos-and-coaches, but modifications during the development programme led to the vehicles being renumbered and reclassified as a unit train because the heating/aircon circuits were not standard ETH connections, so the carriages could not take ETH/Aircon from anything other than an HST power car.
- The locos 41001 and 41002 became coaches 43000 and 43001 (no loco has a TOPS number ending 000 - locos D5000, D8000 and D9000 were renumbered 24005, 20050 and 55022 respectively) and the coaches were renumbered from the 1xxxx series (used for Mark 3 LHCS) to 4xxxx.
That HST trailers are not LHCS was illustrated when the Class 91s were first introduced. As their production was running ahead of that of Mark 4 coaching stock, some of them were put to work hauling HST sets. However, one power car had to remain in the formation as the Class 91 could not provide ETH and aircon for the HST coaches. (The HST power cars were modified to emulate a Mark4 DVT to allow push-pull operation and, after some failures due to spending too long running at idle speed, were also used to augment the traction provided by the class 91, producing some very lively performance).