Like I dunno, the 6th? Called it b3 tho. Yes it has some stuff that is still being worked on, and I know about the pyramid base on the one side of the skybox.
Feel free to noclip around; might help to do r_fastsky 1 before doing so to find the skybox.
Been working with external lightmaps (one of the reasons the bsp is so small, and there's those mysterious tga's in the maps/beta3 directory)
remember you need the internal wfa mapper's build to see the skyportal stuff, so head into #wfamaps at irc.enterthegame.com if u don't have it and ask someone.