Quake Live developer sponge has announced on IRC that the upcoming patch is now available for everyone to test on steam. To get access you just have to open the steam game properties for Quake Live and enable the beta branch under the "Betas" tab.

Sponge IRC Quote
<sponge-> if anyone wants to try out the new quake live, just right click quake live on steam, properties, beta, and opt into the beta branch
<sponge-> we're basically at a near release candidate state!

As was previously announced this update will remove support for the standalone launcher and move the game exclusively to steam, bringing with it support for the steam workshop, in-game achievements, voice chat support and lobbies among other things.

Sponge has also announced the move of the official forums to the Steam Community forums and recommended archiving any useful threads or information on Steam, in the form of forum posts or guides as the current forums will be shut down once the update is live.

Links: QuakeLive update announcement, Forum move announcement