Meta’s Threads app is coming back down to Earth after a blockbuster first week that saw the app become the fastest growing of all time. New data from analytics firm SimilarWeb suggests that the app’s engagement has since declined from initial highs despite its status as the fastest-growing app of all time.

Threads saw daily active users decline from 49 million on July 7th, to 23.6 million on July 14th, SimilarWeb writes in a new report. And in the United States, which reportedly saw the highest engagement, usage declined from 21 minutes per day to just over six minutes in the same time period.

While SimilarWeb cautions that its data is based only on Android usage of Threads, its findings line up with those of other companies. Market intelligence firm Sensor Tower reported a similar decline in engagement, writing in a report that the app “has experienced a double-digit decline in DAUs [daily active users] and user engagement since launch.”

On some level, the drop-off is expected. Threads launched at a moment when many Twitter users were seeking alternatives, and its ties to Instagram made it extraordinarily easy for users to sign up and port over their existing social graph. At the same time, the app is missing a lot of basic features, including a non-algorithmic feed not easily dominated by brands and influencers.

In a Threads post on Friday, Instagram’s top exec, Adam Mosseri, suggested the company wasn’t particularly focused on engagement metrics at this stage. “Our focus right now is not engagement, which has been amazing, but getting past the initial peak and trough we see with every new product, and building new features, dialing in performance, and improving ranking,” he wrote.

Whether or not Meta is able to fully take advantage of those conditions, though, will likely depend on how quickly it can add new features to keep its users coming back, as well as whether it’s able to launch within the European Union. The company is also dealing with issues around spam, according to Mosseri, who said Threads would be putting rate limits and other protections. “Spam attacks have picked up so we’re going to have to get tighter on things like rate limits, which is going to mean more unintentionally limiting active people (false positives),” he wrote.

While the declining engagement with Threads may seem like good news for Twitter, the company still has plenty of reasons to worry about its latest competitor. As SimilarWeb’s Senior Insights Manager David Carr writes, there are “some signs” that at least some of Threads’ engagement has come at the expense of Twitter’s. “In the first two full days that Threads was generally available, Thursday and Friday, web traffic to twitter.com was down 5% compared with the same days of the previous week and Android app usage, by time spent, was down 4.3%,” Carr says. He also notes that “Twitter user retention has been on the decline” since last year.