It's based on the existing 650S, but more powerful, with 675 metric power (geddit?) and 666 hp. The LT bit is short for 'Longtail' and refers to the active airbrake on the back.
What else? It's got a 3.8 litre V8, a 0-62 time of 2.9 seconds and a top speed of 205 mph. That'll do.