Although most of the API changes were previously announced, the overview of the final API highlighted some that were previously unknown. The one sure to cause the most immediate frustration: Twitter is ending support for RSS, XML and Atom.

While it was easy to see the loss of XML coming — Twitter has slowly dropped support for XML in favor of JSON over the last year and a half — dropping support for RSS and Atom is a major shift.

via New Twitter API Drops Support for RSS, Puts Limits on Third-Party Clients.