«Twitter has also grown exponentially in the years since the library started its collection. That year, 2010, about half a billion tweets were posted every two weeks. In November, that many were sent each day. The messages are now longer: The company recently doubled its limit for tweets to 280 from 140 characters. Such complications have plagued public access to the archive, too, which is limited while the library works to find a cost-effective and sustainable way to open the archive to the public».
Source : The Library of Congress No Longer Wants All the Tweets – The New York Times