Mir 0.0.8 came a couple weeks ago and since then there's been numerous developments for this Linux display server that's developed by Canonical for Ubuntu Linux on desktop and mobile devices. Mir 0.0.9 isn't a breakthrough release for this Wayland competitor, but it does have a lot of fixes and improvements scattered throughout. The Mir 0.0.9 release happened on Sunday.
For end-users, one of the visible changes with Mir 0.0.9 is that it now supports VT switching to move over to a virtual terminal via the Ctrl + Alt + Fn keys without killing or losing the Mir session.
There's been almost 100 revisions to the Mir Bazaar repository since the 24 July 0.0.8 release. Some of the other changes include various Android improvements/fixes, the --nested-mode Mir option for configuring Mir-on-Mir, support for monitor input channels from the shell, platform abstraction for graphics handling is now split off into its own (LGPL-licensed) shared library, display change events are now sent to Mir clients with the API/protocol, documentation improvements, and much more. The lag fix deals with addressing the lag time on the Mir compositor side with the time between input events and reaction on the screen.
With no public release announcement, other Mir 0.0.9 changes can be learned by looking through the Mir Bazaar Launchpad log.