Here's the official changelog for Twitter UWP v184.108.40.206 (note that some items are for the PC only):
- We’re changing replies so that you have all 140 characters to express yourself. When you reply to a Tweet, @usernames will not automatically be added to the beginning of the reply, giving you all 140 characters to use in your response. You can see the full list of participant usernames in the conversation by tapping the prompt above the Tweet.
- We added a ‘Tweets & Replies’ tab to Profiles.
- Hold ‘Ctrl’ key and then click to create a new tab.
- We improved the display of images & video in Moments.
- The Live events page now supports multiple timelines.
The biggest cosmetic glitch is that user profiles aren't shown properly, with text corruption and with '0' follower counts. But I'm sure this will get fixed up soonish. In the meantime, some screenshots of the new version of Twitter in action: