As streaming becomes a bigger and bigger part of video games, it's not exactly surprising to see Valve jump into the action with today's newly announced Steam Broadcasting feature.
In its current form, Steam Broadcasting is pretty different from Twitch. There are no archives, no ads, and everything lives through Steam. You simply click on "watch game" while a friend is playing, and a broadcast begins. It's on-demand.
It's possible Valve could eventually develop Steam Broadcasting into a competitor for Twitch, but it seems more likely Valve wants to encourage players to purchase more games.
Right now, Steam Broadcasting is in beta, but you can get in by joining the Steam beta program. Valve warns bandwidth might be limited, however, so if a stream doesn't start, that might be your answer.
More details are available on the Steam Broadcasting website.