Porsche is extensively testing this model.
This one appears to wear the same light concealment as other examples of the upcoming GT4 RS. The engineers continue to put a covering over the top of the front wings/fenders that are likely concealing vents like the ones on the previous-gen GT3 RS.
Gallery: Porsche 718 Cayman GT4 RS Spy Photos
There is also something affixed to the top of the windscreen on the passenger side. This is likely a sensor of some kind or an antenna for sending back telemetry to the track-side engineers.
Compared to the standard 718 Cayman GT4, the RS gains NACA ducts in the bonnet and larger openings in the rear quarter panels. There are also now inlets occupying the back portion of the side windows. At the back, there's a huge, swan-neck wing with similarly large endplates.
Mechanically, the Cayman GT4 RS reportedly has a naturally aspirated 4.0-litre flat-six engine making 500 bhp (373 kilowatts). The gearbox options aren't currently clear. As a possible hint, the latest 911 GT3 adopted a six-speed manual and a seven-speed PDK with a gearshift that makes it look like a manual.
While not easily visible here, there are almost certainly suspension and brake upgrades to match the extra power. It rides on centre-lock wheels.
Given the long testing regimen for the GT4 RS, we expect this model finally to debut soon. Sales should start this year, too, putting the long wait to an end. An earlier rumour suggested the model would have an asking price of $130,000 (£95,000). For comparison, the new 911 GT3 goes for £123,100.