So a reverse Google image search of that “tumblr is shutting down” helped me find the website that’s from. It’s sopastrike.com. And under their “Confirmed”, no where does it list tumblr. Staff has not told us. Tumblr’s twitter account has not made an announcement. If they are, they have yet to come out and say it.
Google is your friend.
Also, if you manage to find a source that shows that Tumblr as a whole is striking, please let me know. I don’t want to spread misinformation.