Bluesky may still be the underdog in the race for alternatives to X, but the once Twitter-affiliated service is gaining momentum. The app just passed the 15 million user mark after adding more than a million new users over the last week, the company said in an update.

While Bluesky is still considerably smaller than Threads, which with 275 million users is its biggest rival, there are signs that Threads users have been increasingly curious about the upstart. “Bluesky” has been a trending topic on Threads in recent days and an in-app search suggestion shows there are more than 19,000 posts about “Bluesky.” Bluesky itself has also made a push to win over Threads users in recent weeks by posting regularly on the Meta-owned service.

That effort seems to be working. A month ago, Engadget noted, the service had just under 9 million users. Its mobile app also has the top spot in Apple’s App Store, followed by Threads and ChatGPT. Its recent success also seems to be driven, at least in part, by frustration with Elon Musk and X following the US presidential election.

A recent report from web analytics company SimilarWeb found that “more than 115,000 US web visitors deactivated their accounts,” on November 7, “more than on any previous day of Elon Musk’s tenure.” The report also noted that “web traffic and daily active users for Bluesky increased dramatically in the week before the election, and then again after election day,” with Bluesky at points seeing more web traffic than Threads. (Threads’ mobile usage, however, is still “far ahead” of Bluesky.)