Besides security fixes, this new update lets us set a default category for new posts. I have set it to #community for now. Other than that, there are fixes to the new sidebar interface that will be enabled as part of our Fall Cleaning: simpler navigation, new server coming that is still planned for some time during the next few weeks.
This was followed one day later by another security update, 2.9.0.beta14, which I applied. That should have introduced no new site behavior, so I’m not announcing it more widely.