Right now the latest version of RAT is 5, but PRMan 11 is coming soon so I expect to either see RAT 5.5 or 6
PRMan 11 will include GI, caustics, etc. This should be a major overhaul, I'm really looking forward to it!
Red bellows of flame have blackened my stones
Convulsing my frame and cracking my bones
Hell's dragons of steel who roar in their chains
Crawl into my caves to suck out my veins.....
-The Mountain P.F.M.