The Pentax 645D IR is a special version of the Pentax 645D with the infrared filter in front of the sensor removed.
This is the first such DSLR from Pentax, though third parties can convert many regular DSLR cameras to support IR photography as well.
The 645D IR can be used for normal photography if you put an IR blocking filter in front of the lens. Apart from the removal of the IR filter, the camera itself is identical to the 645D.
Pentax Ricoh Imaging Co. announced this camera on December 12, 2012 and anticipates a very limited production run of about 100 units per year.