This video highlights a few of the new features of mental ray found in Autodesk 3ds Max 2014. Some of these include rendering an AO pass on the hardware GPU as well as disabling Final Gather and using Image Based Lighting (IBL) to illuminate your scene. Also detailed is a new, more granular method of antialiasing, among other features.
The mental ray string for GPU mrAO used in this video is...
"ambient occlusion gpu" on
"ambient occlusion framebuffer" "fb_re#0"