It's been 16 days since WWDC, when Apple released the first developer betas for iOS 11, macOS 10.13 High Sierra, watchOS 4, and tvOS 11. If you're one that's been willing to put up with the various bugs in the first build, you'll be pleased to hear that the second betas are now available for each, along with Xcode 9, macOS Server 5.4, Classroom 2.1, and Apple Configurator 2.5.
The news was all a bit surprising. Historically, the second developer beta would be released on a Monday or a Tuesday, and it's almost always at 10am Pacific Time. Of course, today is a Wednesday, and the builds were seeded in the middle of the afternoon.
All of these are major updates, so it's quite understandable that the first builds were loaded with bugs. Presumably, this build will be better, although still not perfect. To make things easy, we'll just say that the release notes cite quite a few resolved issues, but there are also still a bunch of known issues and even some new issues.
It seems likely that this is the build that Apple has deemed worthy of a Public Beta, as it promised public releases for iOS 11, macOS 10.13 High Sierra, and tvOS 11 before the end of the month, and a new developer beta doesn't seem likely by then. With this in mind, one might speculate that there could even be a Public Beta by the end of the week.