You are welcome to participate in the Open Beta freely by switching to the Beta build in Steam. Right-click your entry for VRChat in Steam, select the Properties menu, and click the Beta tab. Select
open-beta from the dropdown list. Press OK, and Steam will update you to the latest version of the Open Beta. If you don't see the option, VRChat is not currently running an Open Beta.
As an important note, if you're on the Open Beta, you will usually not be on the "Live" version of the game. In other words, you will be unable to see users on the current Live release if you are in the Open Beta. The Open Beta is meant primarily for testing and feedback.