We already mentioned in our Phenom II X4 965 that the next logical step for AMD is to intro six-core processors. It is now confirmed that the company will indeed release six-core desktop processors next year, the processor will be backwards compatible with existing AM3 and AM2+ motherboards.
AMD's chip is codenamed Thuban and will feature all six cores on single 45nm die. Thuban will feature an integrated DDR3 controller. The company didn't confirm branding but the chip is expected to be labeled as the Phenom II X6. The chip is derivative of the six-core Opteron chip which made its earlier this summer.
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.
Thuban is not due until sometime next year and is unlikely to beat Intel's Gulftown to stores shelves. Intel's Gulftown, likely to be called Core i9, when it is released, will slip into existing LGA1366 boards and will offer 12-threads to the OS with six of those coming from cores, and the other six from HyperThreading.