PCIe 1.1 compliant - it's in the motherboard manual.
But if you mean can you use a PCIe 2.0 card in it, yes you can and it will run at PCIe 1.1 specs. Instead of running 8GB/s for x16 like it would in a PCIe 2.0 slot your PCIe 2.0 card will run at 4GB/s for x16, about the same as a PCIe 2.0 x8 slot would run ...