Mayer's Yahoo will be paying $1.1 billion for Tumblr, most of it in cash, but the social network will continue to run independently.
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Both Karp and Mayer used their blogs to assure users that Tumblr will continue to function the same, with Karp staying as CEO and continuing to lead the company. Tumblr will also continue to be based in New York. The only difference, they said, is Tumblr will now have Yahoo's resources to improve quickly.
"So what's new? Simply, Tumblr gets better faster," Tumblr's Karp, 26, said on his post. "The work ahead of us remains the same -- and we still have a long way to go! -- but with more resources to draw from."
As for any users concerned that Yahoo may make Tumblr uncool -- the way it has with many of its past acquisitions (read: Flickr, Del.icio.us, GeoCities, etc.) -- Mayer said "We promise not to screw it up."
"Tumblr is incredibly special and has a great thing going," she said on Yahoo's Tumblr blog.
Mayer also revealed that Tumblr is now receiving more than 300 million unique users per month. She said the acquisition could grow Yahoo's audience by as much as "50% to more than a billion monthly visitors."
Yahoo has a news conference scheduled in New York for 2 p.m. PDT where it is expected to discuss the acquisition.