The final version of the Configuration Manager 2012 SDK has been released. You can download it from here: http://www.microsoft.com/en-us/download/details.aspx?id=29559.
Documentation can be found here: http://msdn.microsoft.com/en-us/library/hh948960.aspx.
If you had been using the client messaging SDK from the RC version of the SDK, there have been numerous fixes and improvements in the RTM version thanks to some great feedback collected during the RC period. Please make sure you update to the latest version of this SDK if you had been using the RC bits.