Tony said it was in pre-alpha back during E3. I don't know about now, but to answer the stages of development.
Alpha is the stage where you can play the game from start to finish without any crashes (this may mean that sound and music is minimal, shading and lighting effects may still need work as well). Beta is when the game is almost in it's final form, but still needs testing for glitches, bugs, exploits, etc. That's the description in a nutshell though, and, really, that's about as far as my knowledge goes.
Uncharted 2 Machinima Voice Actor. Currently playing Sully and Lazarevic. Add me on PSN if you want to get involved: Geo_Chronic.