Due to be revealed at the 2018 Detroit motor show in January, the hybrid four-door coupé is part of the latest-generation CLS line-up that was launched at the recent LA motor show and kick-starts a range that'll sit below AMG's 63-badged models.
The CLS 53, spotted testing on the public road for the first time, is powered by a 3.0-litre straight six engine, as used by AMG's 43 models, in conjunction with a 67bhp electric motor to produce a total of 429bhp.
The hybrid CLS is expected to come with regenerative braking technology to help replenish its lithium ion batteries when on the move. This technology is already in use elsewhere in Mercedes’ range and would come as part of 48V electrical architecture.
The CLS 53 development car caught in the video above offers few clues as to what design changes we can expect with the AMG model. Most likely, it'll receive AMG wheels, different bumpers and a lower ride height, but the car's luxury focus should ensure the changes will be discreet.
Following the CLS 53, an E53 will be launched with the same six-cylinder hybrid powertrain. This will be the only powertrain available on AMG coupé and convertible E-Classes, while larger saloon and estate models will remain as E63s with V8 engines.
AMG boss Tobias Moers confirmed to Autocar in LA that the '53' nomenclature will feature exclusively on AMG models that use petrol-electric hybrid powertrains. Recent sales from Porsche, which has sold 60% of its latest Panamera in hybrid form, show that global market demand for high performance hybrids is surging.