I just went to the Audi dealer and asked for a litre for my car. It was about £8 plus vat and was actually 1.5 litres.
It's quite likely it's the same as other brands of coolant, but for the sake of a couple of quid I thought I'd get the proper stuff.
As Adam says, G12 plus plus was written on my bottle.
Looking at the expansion bottle on the car should tell you too. I've just noticed mine has G12 written on it.