UPD: looks like this feature was rolled out to all clients.
As I mentioned in Twitter, this time Instagram got a complete new UX element. This side-bar can be easily swiped from the right so you don't need to move your finger to the top of your screen. I would assume that they want to check if these menus will perform better in case if you will have an easier access to them. This UI change will definitely make it easier.
Additionally, the Settings icon was also moved to the bottom of this sidebar. I would imagine that it will take a couple of seconds from people who don't expect it to be there.
I also discovered one more new feature but I am not sure if it was introduced in this update. Now you can link to your IGTV videos from your story. This probably can be a good feature to promote videos from your IGTV channel.
What do you think about this new sidebar?