OS X 10.11.5 focuses on security enhancements, performance improvements, and bug fixes to address problems that have surfaced since the release of OS X 10.11.4. As with prior betas, the changes appear to be mi**r in scope, and ** obvious outward-facing tweaks have been discovered in the first three OS X 10.11.5 betas.
We'll update this post if any new features are found in the Fourth beta.