AMD confirmed it will release a six-core desktop processor in 2010. The chip maker told MaximumPC that the hexa-core CPU is codenamed Thuban, it's a 45nm part and the interesting thing is that will be backwards compatible with existing AM3 and AM2+ motherboard. The product's name isn't official yet, but unless AMD does another makeover of its naming scheme the Thuban will likely be introduced as the Phenom II X6.
Extrapolating from the hexa-core Opteron, Thuban is likely to be a 346mm2 chip and have a massive 904 million transistors. As a comparison, Intel’s Core i7-975 Extreme Editions have 731 million transistors on a 262mm2 die, the Core i5-750 has 774 million transistors with 296mm2 die and the Phenom II X4 965 Black Edition 758 million transistors on a 258mm2 die.
The chip is expected to have 3MB of L2 and 6MB of L3 cache. The company did not specific initial clock speeds but they are not expected to be as high as the quad-core parts. That’s likely due to added thermal output from the two additional cores.