It looks like they've just taken the release that we've already had (4.0.249.30) and made it more public. If you've already had the developer channel build, then you've already got it. Please correct me if I'm wrong.
If you're on the developer channel you'll continue to be on the developer channel. That is, eventually a stable 4.0 release will happen, but because you're on the dev channel you'll be updated to an unstable 5.X beta.
At least that's how it is on Windows.
Looks good, imported all my bookmarks from Firefox, seems really snappy and responsive. Unfortunately extensions do not currently work under OSX, so no AdSweep extension. Once extensions work I'll give it a shot at replacing Firefox on my desktop. I can't go back to the web with advertisements, I just can't.