This update also include an update to the L4D2 Authoring Tools

- Added the Extended Mutation System
- Included demo EMS modes Holdout, Dash, L4D1
- Added support for Linux

- Server operators can now specify whether or not custom content is allowed when playing on their servers. This can be set on a per game mode basis – see cfg/addonconfig.cfg for details.

- Fixed yellow screen corruption that occurs on AMD Radeon HD 6000 Series hardware.
- Updated database to include video cards from the Steam survey through April 2013.

Add-ons
- If a found game is using a Mutation add-on from the workshop, the "Download Add-on" button will open the workshop page
- Adjusted add-on sorting when loading the main menu so Mutation add-ons can override UI elements.
- Reworked add-on management to improve stability and properly support custom mutations.
- Fixed the download progress panel sometimes not updating because it was referencing a different file than the one currently downloading.
- Added a drop-down menu to the add-on screen to filter by tags.
- Fixed occasional focus problem when clicking on the Addons list panel.
- Allow keyboard scrolling of the Addons list panel.

Publishing Tools
- Fixed published file browser not updating after publishing new content.
- Fixed published file browser showing only the first fifty items of a users workshop.
- Fixed upload tool throwing an error when replacing an existing file, if the file size was greater than the available space in the cloud.
- Fixed upload tool sometimes showing an error dialog for files that had been deleted from workshop.

Changes:
- Fixed a possible buffer overflow in keyvalues
- Fixed player_death event setting "victimname" to "Charger" when the Spitter gets killed.
- Fixed a bug that sometimes caused the rescue vehicle to arrive immediately when the second team in a versus match started the finale.

Left 4 Dead 2 Workshop Manager
- Updated scheme
- Added new tags
- New field for change notes when editing existing workshop items

- Added support for dedicated servers to load addons from the "workshop" subdirectory. Fixes consistency errors when playing workshop campaigns on dedicated servers.

NOTE TO SERVER OPERATORS: To host workshop campaigns on your dedicated server, they should now be placed in the same location as on the client (/left4dead2/addons/workshop/…) Campaigns not downloaded from the workshop can still go in the "addons" directory.

Custom Campaign select screen:
- Show all installed custom campaigns, not just the ones that support the current mode.
- Disable list items for campaigns that don't support the current mode, and sort them to the bottom of the list.
- Fixed some uninitialized text fields when no campaign is selected.
- Moved an informational string so it doesn't overlap the campaign list.

Workshop Publishing Tool:
- Removed the file count from the download progress bar to avoid confusion when stale meta-data indicates there are more files than actually exist.
- Don't show the download progress bar if no valid files were found.
- Fixed the "Failed to write file chunk…" error message not correctly showing the number of bytes written.

- Fixed Workshop add-ons not mounting correctly on the Mac

- Updated a Steam binary that may have been causing some Windows Dedicated Servers to crash

• Workshop now available for Left 4 Dead 2.
• Added Workshop Manager upload tool to Left 4 Dead 2 Authoring Tools.
• Add-ons screen now supports browsing the workshop and subscribing to workshop content.
• Moved add-on menu option to main menu
• Added the ability to filter add-on content by tags.
• Fixed scoreboard not showing the campaign name for custom campaigns.
• Fixed "Rescue" label not drawing correctly in the scoreboard for campaigns with more than five maps.
• Cleaned up DLC add-on file dependencies and simplified talker file structure - the manifest has changed.
• Fixed an issue where some L4D1 vocalizations that were also present in L4D2 weren't firing.
• Fixed transition dialog in L4D1 campaigns.
• Various fixes for character dialog including conversations, weapon spotting, defibs, and other misc audio.
• Added data on L4D1 characters so corresponding Talker rules would work (ie Elevator Speech in No Mercy)

- Updated menu navigation for Big Picture Mode so the joystick doesn't always have to be active

- Fixed the Tank's primary attack sometimes choosing different sequences between the client and server. Fixes hit traces not always matching the visible animation.
- Fixed the Tank's left-handed attack using the right hand's position for hit traces.
- Player-controlled Tanks now always choose the right arm horizontal swing sequence for primary attacks. Fixes some attacks not connecting when it appears they should have, due to the inability to predict which swing animation would be randomly chosen.