The K-processors are the unlocked ones that are very easy to overclock with push of a button. The newest unlocked CPUs are i7-4790K and i5-4690K. i7-4790K has the base clock at 4.0 GHz, boost at 4.4 GHz, with 4 cores and 8 threads, while i5-4690K has base clock at 3.5 GHz, boost clock at 3.9 GHz with 4 cores and 4 threads.
The processors works with 9-series intel chipset, such as H97 and Z97. According to the picture the unlocked CPUs will be released mid 2014.