Microsoft released the dynamics CRM 2011 software development kit version 5.0.12 on August 17, 2012. This SDK coincides with update rollup 10 for Microsoft Dynamics CRM 2011. It also looks like Microsoft skipped a version number like they did with rollup 10. There is a long list of new functions and updates they can be found in the crmsdk2011.chm help file in the SDK root directory.
You can download the SDK here: http://www.microsoft.com/en-us/download/details.aspx?id=24004
Rollup 10 is available here: http://www.microsoft.com/en-us/download/details.aspx?id=30711
The knowledge base article for rollup 10 is available here: http://support.microsoft.com/default.aspx?kbid=2710577