A user from facepunch found that there are multiple graphical improvements in the way
http://facepunch.com/showthread.php?t=1415582&p=45619337&viewfull=1#post45619337
The editor references source engine 1.0 here:
The editor compiles to a new map format, vmap_c
It also uses a new model format, vmdl.
You can import tgas, FBX files, and here's a list from facepunch of the rest:
• Brushes are now meshes and act like models. You can edit by face, edge, and...