New model has retractable hardtop, and a 441kW 3.8-litre twin-turbo V8.

The McLaren 600LT Spider has been unveiled, becoming the fifth model to wear the Longtail name.

Like other Longtail models, the 600LT Spider will be built in limited numbers – exactly how limited isn't clear – and is significantly lighter than the car on which it's based.

When fitted with the full gamut of optional lightweight features, things like titanium wheel bolts and carbon-fibre racing seats, interior trim, and wheel arch louvres, the 600LT Spider tips the scales at 1297 kilograms, or 100kg sprightlier than the 570S Spider.

The Spider shares much of its carbon-fibre body, as well as the fixed rear wing, Pirelli P-Zero Trofeo R tyres and retuned steering, with the 600LT coupe launched late last year.

Those who want to shave a few extra kilograms can also delete the car's audio and climate control systems, although the logic of killing air conditioning in somewhere like Australia is questionable at best. With its power-retractable hardtop and various structural reinforcements, the Spider is 50kg heavier than the 600LT coupe.

Thanks to its shorter exhausts, upgrade cooling system and revised software, the 600LT's 3.8-litre twin-turbo V8 cranks out 441kW of power and 620Nm of torque.

Coupled to a seven-speed dual-clutch transmission, the 600LT Spider can blast from 0-100km/h in 2.9 seconds, and hit 200km/h in 8.4s, or 0.2s slower than the coupe. Top speed is said to be 324km/h with the roof up, and 315km/h when in open-top mode.