GitHub Enterprise 2.6 includes a new feature mix to "create efficient, flexible, and friendly processes [for teams] at every step of their development cycles." In other words, this isn't about the speed of the application, but about streamlining how teams work with GitHub -- how they collaborate on code, merge it, manage it, and discuss it.
Many of the new changes are tools for administrators managing workflows on GitHub repositories. Some of them have showed up before on GitHub's public site, such as templates for issues and pull requests.
Other new features are for use cases that appear more often with GitHub Enterprise deployments. Admins can now set up "pre-receive hooks," which enforce policies for pushing code before it enters the repository. Along with protected branches (another enterprise-grade feature rolled out in 2.5), admins can elect to merge outdated pull requests -- for example, if it turns out they're actually useful -- and restrict branch-merging privileges to specific users or teams.
There's plenty new for the rank-and-file user, too, like the ability to add a file to a repository by simply dragging and dropping it into the GitHub interface. For those who have long had trouble with the Markdown syntax used by GitHub to style issues and comments, the editor now has tools to help out.
Git users have long had the ability to perform a "squash merge," where a batch of commits can be consolidated into a single commit. GitHub Enterprise now supports this as well. This cuts down on the traffic that takes place around a project and reduces the notifications an admin has to wade through for the projects they oversee.
Many of the other time-saving features are little ones, like being able to find and filter files in a repository by name or extension, or to filter changes by commit, with GitHub suggesting this can be used "to see how a pull request has evolved through time."