The main addition is Instagram-Messenger cross-app group chats. It's not a major change, given that the option to chat across the two apps between individuals has been available since last September. But it does add another element, while it's also another step in Facebook's broader messaging integration plan, which, eventually, will also include WhatsApp, enabling users of each individual platform to message others on whatever app they choose.
Facebook is also adding polls In Instagram DMs, which will also be accessible in cross-app group chats. That could provide another engagement option, while the cross-app functionality is, again, another big step in solidifying its integration effort, and melding together its full suite of messaging tools.
Facebook is also adding new group typing indicators, which will show when your friends are typing at the same time. You'll now be able to see when several people are typing at once, which could add to the discussion buzz in active rooms.
Facebook is also adding new chat themes on both Messenger and IG, as well as an 'Astrology art suite', including backgrounds and new AR effects. Astrology has become increasingly popular over the past year, with Snapchat also adding new astrology integrations to boost engagement.
And finally, Facebook will now enable Watch Together from the Instagram Feed, providing another way to spark in-chat discussion and engagement.