I noticed that there isn't a sandbox toggle in the Game Center settings on iOS9. Are we going to be able to start doing beta testing without forcing testers to go into Sandbox mode? That would be awesome.
Sandbox for Game Center
I seem to recall a one-sentence statement in one of the What's New WWDC videos saying that the sandbox and development environments are being merged. What that means, specificially, I don't know.
I found the sanbox enviromnet very different to the “real enviroment”.
The sandbox never lost packets, messages never got lost and arrived very quickly. (This resulted in design desisions based on this experience.)
This was not the case when my game was released and was played in the real world. The result was games that would fail, where they did not in the sandbox.
Sandbox environment has been merged with the live environment now. The sandbox switch is now gone. More info here: https://developer.apple.com/videos/wwdc/2015/?id=605
A brilliant move by Apple.