From casual tweeters to the White House's tweeter-in-chief, the Library of Congress has digitally stored every public post shared on Twitter since the social media platform's inception in 2006.

But starting Jan. 1, the nation's oldest federal cultural institution will change its policy from collecting every tweet to saving ones on a select and more scrutinizing basis. There are an average 200 billion tweets sent each year, according to tracking site Internet Live Stats.

The Library of Congress on Capitol Hill. J. Scott Applewhite / AP file

With the new guidelines, the Library announced in a press release Tuesday, "the tweets collected and archived will be thematic and event-based, including events such as elections, or themes of ongoing national interest, e.g. public policy."

In 2010, Twitter gifted the Library the "entire archive of public tweet text beginning with the first tweets of 2006 through 2010," continuing with all tweets made after that time.

"The Library took this step for the same reason it collects other materials — to acquire and preserve a record of knowledge and creativity for Congress and the American people. The initiative was bold and celebrated among research communities," the release said.

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But the Library gave several reasons, including the "explosion in use," changes to terms and services, and modifications in functionality for why the agreement with Twitter was being altered.

The Library says it will continue to preserve and secure its collection of tweet text, and work with Twitter to acquire tweets selectively.

For people hoping to actually pore through all of the tweets, however, that's still not possible. The Library said its Twitter collection won't be available to the public until access issues can be resolved in a cost-effective and sustainable manner.