The title says it all. Link to download: http://www.adobe.com/support/downloads/thankyou.jsp?ftpID=5488&fileID=5498
Raw support for the D600 was a total surprise because the 4.2 release candidate didn't have D600 support and DPReview was mentioning that they used a 4.3 private beta to convert D600 raw files.
LR 4.2 includes this disclaimer about the D600 support:
* Please note that the support for Nikon D600 is preliminary and there is a minor risk that the appearance of your images may change when the final support for Nikon D600 is available in an upcoming release.