Changelog and instructions to try it. It will be free until some time before release.

How to change to testing branch in Oxygen Not Included (Steam)

In Steam, click on Library > Games.
Scroll down to Oxygen Not Included.
Right-click and select Properties.
Go to the BETAS tab.
In the dropdown, select the name of the branch you want to play. In this case, the branch name is "public_testing"
    This branch does not require a password.
In that same Properties window, go to the Local Files tab and press "Verify Integrity Of Game Cache."
Your game will be updated to the the previous branch.
Launch and play Oxygen Not Included"