We have had plenty of people asking about the L4D2 Beta showing up in their steam catalog. So in case you missed it or were confused, here is some more info.

Currently, changes to L4D2 will first appear in the Beta before they appear in the main game. The Beta will change often. This mean this build is very active so you might want to avoid it if you have bandwidth caps. Today we released another update for it. You can read the release notes for the update here.