I was able to use it for free without a wait.

"We’re happy to confirm the new Bing is running on GPT-4"
[link to twitter.com (secure)]

1. Install Edge (also available for mac)
2. Create/Sign-in to account
3. In an Edge sign-in, visit bing.com/new and Join Waitlist. on macOS I was approved immediately.
4. Relaunch and/or wait some time for it to activate
5. Use the chat/compose from bing.com/new. It's also supposed to work from the browser's built-in Discover pane (click blue 'B' in top-right of window), but that wasn't working for me.

-It will say "Searching for [keywords]" before it generates a response.
-There are limits in place.