[boost] [phoenix] What is its state of play?

Hi I've just started looking at the Boost.Phoenix library, from a cold start, and I'm a bit confused! What version is current atm? It seems to be in flux between v1.2.1 and v2.0. Also, if someone could say a few words about any relationship between Phoenix and Lambda I'd really appreciate it. Does Phoenix replace Lambda, complement or coexist with it? Many Thanks, Rob.