The third beta of OS X 10.11.6 has just been seeded to developers. We see this release two weeks after the last one. With this version of El Capitan, we find some bug fixes and security improvements. Other than that, there are no other outward changes that the user will notice.
To get this version, developers can go to the Mac App Store and get it from the updates page. If this version is not yet installed, they can download it from the downloads page in the Apple Developer Center.