The Larrabee-derived Xeon Phi will initially be in the form of a Xeon Phi 5110P card, which consists of 60 cores on its "Many Integrated Cores" architecture running at 1GHz with 8GB of GDDR5 video memory. The Xeon Phi 5110P will be available in January of next year while launching later in H1'2013 will be the lower-end Xeon Phi 3100, but there's less details about on that MIC card. The Xeon Phi 5110P will be initially priced at $2649 USD while the Xeon Phi 3100 is said to cost below $2000 when that product family launches.
More details on the new Xeon Phi products can be found with the Intel Delivers New Architecture for Discovery with Intel Xeon Phi Coprocessors press release. Xeon Phi hardware is already found in the Beacon super computer on the Top 500 super-computer list.
There's already open-source Linux support for the Xeon Phi on Linux with modifications to GCC and the Linux kernel. The many-core co-processors can be tapped using OpenMP and other programming models.