German tuner 9ff is proposing to build a speedster version of it extreme 1120bhp 9ff GT9R.
Although details are slight, an artist's rendering of the car was displayed on 9ff's new dedicated website for the United Arab Emirates. Underneath the image, it said: 'Fastest Car in the World - 257 MPH - Now available as Coupe or Convertible'.
The convertible version of the car is expected to be based on the coupe model, which is sold by 9ff as 'the world's fastest street-legal car'. Performance figures of 0-60mph in 2.8 seconds and a 257mph top speed are claimed.
Power comes from a tuned version of Porsche's 4.0-litre flat six, which is mid-mounted and mated to twin-turbos to produce 1120bhp and 774lb ft of torque.
The coupe weighs 1326kg, which will increase with the weight of a folding roof mechanism and the additional body strengthening required.
Just 20 versions of the coupe are slated to be built and prices are not known. However, the convertible version is likely to be just as exclusive, with speculation suggesting it will be sold in the Middle East only.