Development of the SL was, for the first time, handled entirely by the Mercedes-AMG performance division in Affalterbach - and the GT will essentially serve as a hard-top coupé version of that car, sharing the bulk of its underpinnings.
As such, the stylistic differences – even through the heavy camouflage worn at this early testing stage – look to be limited chiefly to a more rakish rear roofline and a bespoke treatment for the front grille. When it is eventually revealed, unique wheel designs, paint colours and option packs could be introduced to further differentiate the cars.
The current-generation GT is exclusively a two-seater, but with the SL adopting a pair of rear seats for the first time in several generations and direct rivals in the form of the Porsche 911 and Ferrari Roma carrying a pair of child-sized buckets in the rear, AMG could see fit to expand the cabin. It is not clear in these photos how different the GT's interior will be from that of the SL.
The GT can be expected to follow largely the same formula as its convertible sibling. It rides on the same all-new aluminium platform, claimed to boost transverse rigidity by 50%, which allows the engine and axles to be mounted lower in the chassis. It is unclear whether the GT will follow the SL in making the switch to a four-wheel-drive layout, but it is likely to use the same rear-wheel steering system for improved cornering performance, while the electronically controlled limited-slip differential could be fitted as standard.
It will also use the same twin-turbocharged 4.0-litre V8 as the two SL variants already revealed, although likely in just the more potent state of tune, with 577bhp and 590lb ft for a sub-4.0sec 0-62mph time and a top speed nudging 200mph. A plug-in hybrid GT 63e variant should follow soon after, using a variation of the 831bhp electrified V8 deployed in the new AMG GT 4-Door Coupé PHEV.