New content delivery system which allows diff patching (and installing to other than default folder in the beta). Recent releases already use it, the back catalogue is gradually being converted.

Ah. Ok. Guess patching no longer means downloading half the game in some cases. I just wish Steam would do that in the background like they do everything else. The reason I use this client is so they do it while I'm doing other stuff!

That's exactly why they introduced it. Bandwidth is expensive.

I assume it will convert the game content to a new efficient format. :3