To access the beta right click on the game in the library and press properties, then navigate to the beta tab and select "public_beta" in the dropdown. You may have to restart steam if the game does not start downloading the beta.
Patch notes:
- Fixed issues where downloaded content would not show up in the campaigns list
- Added tabs for different type of content in the campaigns menu
- Added icons for different type of content in the workshop browser
- Loading downloaded battles in sandbox mode now displays the correct image