Apple has released the fourth beta of its iOS 6 software to developers. The build number is 10A5376e and it comes in at just over 280MB for the iPhone 4S. The update is available over-the-air now, though some users are having issues installing it and are getting an error message.
The build appears to be quite a but more stable than beta three. You can view the full release notes on the Apple Developer Portal.
An updated Xcode beta and Apple TV iOS 6 beta has also been released.