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Threads already has over 95 million posts, 30 million signups
(www.theverge.com)
This is a most excellent place for technology news and articles.
Instagram has more than 2 billion active users, and each (non-EU) Instagram user can conveniently login Threads just pressing a button. If they're fudging the numbers, activating only 1.5% of their potential userbase seems odd. Why not activating hundreds of millions of accounts?
As for the posts, an average of 3.2 posts/users for just the first day sounds reasonable to me.