The Steam Link now supports local co-op by simultaneously streaming to multiple devices.
There's no supporting information and the update isn't particularly detailed, but according to the most recent Steam Client patch notes - which note that the patch has been updated since it was originally deployed on 11th October to include a "crash workaround" for the AMD driver on Windows - streaming to more than one device is now available providing you have a "high quality 5 GHz WiFi" network (thanks, PC Gamer).
It also confirms that Android phones can now also be used it as a touch controller, too.
Valve has also addressed a bug which stopped streaming from the in-game Big Picture overlay, and adds a opportunity to select a language before game install if your selected Steam UI language "isn't supported".
Other tweaks come to Steam Chat, including better functionality if you're appearing offline, so the app no longer tries to start chat or open the friends list if you're booting up in offline mode, nor if you clicking Friends & Chat in the overlay whilst offline.
A bug that caused duplicate sounds for friends coming online or going in-game has also been addressed, chat tabs can be scrolled through using the mouse wheel, and you can now test your microphone, too.
For the full details, head on over to Steam.