This release uses the new Twitter REST API version 1.1. The main difference between 1.0 (used by Twitter 7.x-3.0) is that all requests must be authenticated with OAuth.
Since March 2013 Twitter API 1.0 will be turned off so sites using Twitter 7.x-3.0 or earlier must upgrade in order to keep on interacting with Twitter. More details can be found at https://dev.twitter.com/blog/changes-coming-to-twitter-api.