Since it's just a test, though, it's only live for very small number of accounts -- only one Engadget editor has access to it at the moment. That editor has an ordinary account with no YouTube Red subscription, so it's safe to say that the platform isn't giving Red subscribers the special treatment. As you can see in the GIF below, the minimized panel has Pause, Play and even Next controls, so you can keep playing video after video in the background. Clicking on the title underneath the small panel takes you to that video's page.

If that sounds like a great feature to have, you'll have to cross your fingers and hope for the best. Like any other YouTube or Google test, the feature might or might not see wider release in the future.