The third developer beta for OS X El Capitan 10.11.5 is now available from Apple. Interested developers will find the configuration utility needed to install the release can be found at Apple's Mac Developer Resource Center. It can also be installed from the Updates section of the Mac App Store on a machine running the previous beta.
Apple has also released the third version of the OS X 10.11.5 public beta. If you're a member of the Beta Software Program, you'll find the new release in the Mac App Store as well.
It's not known at this time what changes will come with OS X 10.11.5 when it launches publicly. It will likely feature a number of bug fixes and performance improvements.