"We are proud of what the team has accomplished and are happy to have found the ideal partner in Automattic, whose expertise and track record will unlock new and exciting possibilities for Tumblr and its users".
The price comes as a surprise, as the site was previously sold to Yahoo for $1.1 billion back in 2013. Full details of the deal have not yet been revealed, but the micro-blogging service is being bought by Automattic, the company behind WordPress.
Automattic's lineup already includes WordPress.com, Jetpack, Simplenote, WooCommerce, Longreads, and more.
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"When the possibility to join forces became concrete, it felt like a once-in-a-generation opportunity to have two beloved platforms work alongside each other to build a better, more open, more inclusive - and frankly, more fun web", Automattic CEO Matt Mullenwag said in a Tumblr blog announcing the deal.
Tumblr was founded by David Karp in 2007 as one of the first microblogging services.
Tumblr's popularity, and presumably value, took a significant hit at the end of previous year as it responded to a push to limit child exploitation material on the site by deploying an artificial intelligence-powered filter to remove any and all sexually explicit material. Experts suggest Tumblr's mobile interface could be a model for Wordpress.com's mobile platform. Verizon acquired the site as part of its 2017 purchase of Yahoo.
A large number of Tumblr users criticised Verizon for banning all types of adult content on Tumblr, forcing them off of the site. It has cut jobs and sold some Yahoo properties, including the photo-sharing site Flickr and Polyvore, a fashion and collaging site that was then shut down.