Moments basically groups a bunch of prominent tweets surrounding a particular news story or trending topic so that users can quickly check out the trending messages without having to perform a search. The new version number for the official Twitter Windows 10 PC app is 4.3. This is just for the PC app; it has not been updated for the official Twitter app on Windows Phone and Windows 10 Mobile.
Aside from the Moments feature, there's nothing else that appears to be new with the Twitter update on Windows 10. If you do see something new, please let us know in the comments.