Source SDK beta now available.

[Jimmy422]

There is a Source SDK update available now. Please opt into this beta via the Steam UI under File|Settings.

Here are the release notes:

=Enhancements=
-Particle Editor, Material Editor, and Commentary Editor are now included in the Source SDK
-Updated SDK source code for Orange Box mods
-Added example particle system files to SDK content

=Fixes=
-Updated Linux binaries and makefiles for dedicated servers and server plugins
-The Faceposer phoneme editor now pops up a warning message when a phoneme cannot be saved

=Known Issues=
-SDK shaders have not yet been updated for Orange Box games
-New editors can be accessed by adding ‘-tools’ to the launch options for Orange Box games or mods utilizing the Orange Box engine

Source:
http://forums.steampowered.com/forums/showthread.php?t=691717