The Beta badge is achieved by "Actively participating in the private beta." Does that mean the private beta for Stack Overflow (which I believe never happened) or just any site on the Stack Exchange network?
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
- Your voice helps shape the way Stack Exchange operates
There was a private beta for Stack Overflow - it was in July 2008!
The badge is site specific so you get it for a site when you participate in the private beta for that site. It's way too late to get it for Stack Overflow, but if you commit to a site on Area 51 and ask and answer questions in it's private beta you'll the badge for that site.