Spy photographs taken at the Nürburgring show a disguised prototype version of the four-door coupé, confirming that the facelift will feature minimal styling changes over the outgoing model.
Only the front bumper carries any major camouflage, with the rear bumper and other body panels seemingly unchanged from the third-generation CLS that was launched in 2018. Even the front and rear headlights appear unchanged from the current model.
The Audi A7 rival's low-riding suspension may indicate this is a powertrain test mule, which could suggest Mercedes is working on a plug-in hybrid version for certain markets.
While these images don't give a clear glimpse at the interior, the refreshed CLS is expected to feature an extensively reworked interior, in line with the Mercedes E-Class saloon with which it shares a platform. New driver assistance systems, uprated MBUX infotainment technology based around two 10.25in screens, and a new steering wheel design featuring capacitive touch controls are all likely to make an appearance.
When it arrives, the CLS is likely to receive an updated EQ Boost 48V mild-hybrid powertrain, which was refined for the E-Class to deliver fuel economy gains. There's also the possibility of a plug-in hybrid using the same 2.0-litre four-cylinder engine as the new E-Class, which would help Mercedes lower its fleet emissions figures.
An AMG-developed CLS 53 is also expected, though with the AMG GT63 now filling the four-door coupé performance niche, a return for the CLS 63 seems unlikely.
The CLS is expected to be officially revealed towards the middle of 2021. Prices are likely to see a slight increase over the current model, which starts at £66,395 in the UK.