The new vehicle will make its public debut at the upcoming Geneva motor show alongside the 675LT.
Compared to the road going P1, the GTR features an 80mm wider front track, retuned suspension that sits 50mm lower to the ground, and Pirelli slicks wrapped around centre-locking 19-inch alloy wheels.
Downforce has been increased by 10 percent thanks to a new flaps ahead of the front wheels and a 40cm tall fixed rear wing. A drag reduction button on the steering wheel instantly reduces the pitch of the rear wing from 32 to zero degrees.
There's also an aerodynamic blade down the flanks, which is said to clean up air flow along the car's sides.
The hybrid drivetrain has been given a tweak and now develops a total of 736kW. Of that, the 3.8-litre twin-turbo V8 is responsible for 588kW, while the electric motor produces 147kW.
That's up from the 673kW/900Nm hybrid drivetrain used on the road going car, which uses a 542kW/720Nm version of the twin-turbocharged V8 and a 132kW/260Nm electric engine.
The livery on the P1 GTR that will be on display at Geneva mimics that of chassis #06R (below, left) from the mid-1990s McLaren F1 GTR endurance racing programme.
As part of the ownership experience programme, P1 GTR buyers will be able to customise the livery designs on their vehicles, and will have a racing seat tailored to their body shape.
Private track events for P1 GTR owners, confirmed by McLaren so far, include a testing session at Silverstone in England and a meeting at the Circuit de Catalunya in Spain.