Announced and rolled out to Beta Client users in December, Valve has made Steam Broadcasting available in the regular client today. That means you can start broadcasting gameplay right now, or when the new Client Update has properly downloaded and installed.
While broadcasting is the biggest feature in the new update, the frames-per second overlay is now available to the regular client as well (it rolled out to beta testers earlier this month). Most other changes are either fixes or tweaks, though now future game updates will be indicated in the UI. Check out the full update notes over here.
While the new broadcasting functionality is a welcome addition, our own Tyler Wilde thinks it's unlikely to challenge Twitch's dominance in the area.