Have a look on what’s new document of technical in Dynamics AX 2012 for development.
This training material provides individuals with an introduction to the new features and functionality in Microsoft Dynamics AX 2012. The purpose of this training is to introduce new features so that participants can learn about the main differences in the software since the last version.
This training does not cover functionality that has not changed since the earlier versions of Microsoft Dynamics AX 2012. It assumes participants have baseline knowledge of the earlier version.
Have a look on the details here.