Apps that support the new Card functions can be installed directly from a link within Twitter. Currently, that includes apps like Vine, Etsy, Flickr, Foursquare, Jawbone, and Path, among others. When a user tweets from one of the aforementioned third party apps, the tweet will include a link to download the app.
The update also includes faster launch times and performance upgrades along with bug fixes.
Twitter for iPhone now helps you discover, install and launch your favorite apps from Tweets. This update also includes the following improvements:Twitter for iOS is a free app that can be downloaded from the App Store. [Direct Link]
-Faster launch times and general performance upgrades
-"Retweeted by" in Tweet detail is now tappable
-Fix for reply-to-self in conversations
-Fix for bug that prevented undoing retweets in some cases