If you have Gang Beasts on Steam Early Access and want to playtest the three new stages shown in the E3 trailer (the "chute", "elevators", and "tower" stages) you can download the current "unstable" alpha build (it is referenced as "unstable" as it is updated more frequently than the default build and has had less testing).
To download the current "unstable" alpha build right-click on the game name on the Steam library page and select 'Properties' from the dialogue window that opens, from this window select the 'BETAS' tab then the 'unstable' option from the dropdown menu (the menu labelled 'Select the beta you would like to opt into:' (to revert back to the last 'stable' branch select 'NONE- Opt out of all beta programs' from the same menu).
For reference switching between 'unstable' and 'stable' branches of the game forces the selected build to download to the Steam client.
Gang Beasts is an Early Access game and is currently in uninterrupted development, the 0.1.x and 0.2.x builds have bugs, partially implemented gameplay content and mechanics (please see the Steam Early Access FAQ at store.steampowered.com/earlyac... for more information).