Mercedes-AMG will add a third model to its GT Roadster line-up, with the mid-spec GT S set to hit Aussie showrooms sometime next year.

The GT S will slot in between the GT and GT C variants in the Roadster family, matching the coupe line-up with all but the range-topping 430kW GT R, which is built exclusively in coupe guise.

While local pricing has yet to be disclosed, existing pricing structures suggest that customer can expect to pay around $320-$330,000 before on-road costs for the new GT S.

Drive is sent to the rear wheels through a seven-speed dual-clutch automatic transmission, with an electronically-controlled locking differential administering power to the ground.

Like all GT variants, the GT S is powered by a 4.0-litre twin-turbocharged V8 engine, and is tuned to match its coupe sibling with 385kW of power and 670Nm of torque.

Drive is sent to the rear wheels through a seven-speed dual-clutch automatic transmission, with an electronically-controlled locking differential administering power to the ground.

The German rag-top sprints from 0-100km/h in 3.8 seconds, before hitting a top speed of 308km/h.

Distinguishing the car from the entry-level GT Roadster, the GT S features 'AMG Ride Control' sports suspension with active dampers, variable performance exhaust, 20-inch alloy wheels at the rear and 19-inch at the front, 360mm composite rear brake discs and five-mode drive select.

Inside, the GT S is fitted with the 'Silver Chrome' package with the 'Piano Lacquer' package also available as an option.

AMG's 'Airpanel' active air regulation system is also featured as standard, which opens and closes louvres at the bottom of the front apron to optimise aerodynamics and cooling.

Inside, the GT S is fitted with the 'Silver Chrome' package with the 'Piano Lacquer' package also available as an option.

The German rag-top sprints from 0-100km/h in 3.8 seconds, before hitting a top speed of 308km/h.

Detailed Australian pricing and specifications will be confirmed closer to the vehicle's release in 2019.

Do you prefer the coupe or roadster version of the Mercedes-AMG GT S? Let us know what you think in the comment section below.