Interest in Threads, Meta’s supposed ‘Twitter-killer’ app, may already be fraying.

Just a week after the app’s peak usage on July 7, average time spent on the app each day fell from 21 minutes to six minutes among U.S. users, according to an analysis by Similarweb, a digital data firm. The company tracked usage based on the social media service’s Android app.

Time spent on Twitter also took a slight knock over this period, falling by 4.3% (at least on Android). Yet the total, at 25 minutes, was still far above Meta’s competing app.

Daily active users on Meta’s Android app for Threads also fell between July 7 and 14, from 49 million to 23.6 million. Twitter had about 107 million users on July 14, according to Similarweb.

Meta executives suggested that they were expecting a fall in interest. “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,” Instagram head Adam Mosseri wrote on Threads on Sunday, eight days after the app’s release.

“Early growth was off the charts, but more importantly tens of millions of people now come back daily,” Meta CEO Mark Zuckerberg wrote on Threads on Monday, saying the growth was “way ahead of what we expected.” He continued that “the focus for the rest of the year is improving the basics and retention.”

Meta launched its Twitter competitor, built on Meta’s existing Instagram platform, to a massive reception on July 5. Just five days after release, Zuckerberg claimed that the new social media service had over 100 million users.

If accurate, that number would make Threads the fastest-growing consumer app ever, beating OpenAI’s ChatGPT, the previous record holder.

Over a quarter of users for Threads are in India, reports Nikkei Asia citing data from Sensor Tower, a market research firm. The U.S. is in second place, with a 17.6% share of users.

After Meta released Threads, both users and advertisers noted that the app was missing features common to other social media platforms, like the ability to search via hashtags.

Meta decided to release Threads “sooner rather than later” to see “if people were even interested” in the platform, Mosseri wrote on the platform a week ago.

That lack of basic features compared to Twitter may be one reason for the drop in engagement, writes David F. Carr, senior insight manager for Similarweb. Meta’s app “still needs to offer a compelling reason to switch from Twitter or start a new social media habit with Threads,” he continues.

Meta announced new features for Threads on Tuesday, including an easier way for users to see who is following them and a translation function.

A spokesperson for Meta, when asked for comment, referred Fortune to Zuckerberg and Mosseri’s posts on Threads.

Threads vs. Twitter

Meta reportedly accelerated its plans to launch Threads following missteps from Twitter and its owner Elon Musk.

Musk’s policy changes, particularly around content moderation, have unnerved brands and creators. Public figures were interested in a platform that was “sanely run,” Chris Cox, Meta’s chief product officer, said in an internal meeting earlier this year, reported The Verge.

Twitter’s owner has not taken the launch of Meta’s competitor well.

Musk has griped about Threads’ privacy permissions, challenged Zuckerberg to a cage fight, and threatened to sue Meta for poaching ex-Twitter employees and stealing trade secrets. (Meta dismissed Musk’s allegations, saying that “no one on the Threads engineering team is a former Twitter employee.”)

Zuckerberg has also explicitly referred to Twitter when discussing Threads. “I think there should be a public conversations app with 1bn+ people on it. Twitter has had the opportunity to do this, but hasn’t nailed it,” he wrote on the app soon after its launch.

Meta will “need a more compelling value proposition than simply ‘Twitter, but without Elon Musk,’” Anthony Bartoloacci, managing director at the online analytics firm Sensor Tower, told CNBC before the weekend. (Sensor Tower also reported drops in engagement and daily users for Threads.)

Threads is unlikely to completely replace Twitter, social media experts previously told Fortune.

Instead, the world of text-based social media would likely split into multiple platforms that offered different content: Twitter would be for breaking news and commentary, while Threads (like its parent app Instagram) would be for influencer-driven content.

Twitter has its own problems. On Saturday, Musk revealed that Twitter’s advertising revenue was still down by 50%, and that the company had “negative cash flow.”

Update, July 20, 2023: This piece has been updated with a response from Meta.