Twitter last week officially increased the number of characters users can post in a single tweet from 140 to 280. The company first announced the change in September, introducing the longer messages to a select group of users. In a post on the company's blog, Twitter product manager Aliza Rosen writes that during the trial phase, even with the additional characters, only 5 percent of tweets sent by users were longer than the format's original 140 characters. Users given the additional space also tended to use Twitter more, according to Rosen.