Why the Early Success of Threads May Crash Into Reality

Mr. Seufert, the mobile analyst, called the numbers that Threads had racked up “objectively impressive and unprecedented.”

Elon Musk, who owns Twitter, has appeared agitated by Threads’ momentum. With 100 million people, Threads is quickly surging toward some of Twitter’s last public user numbers. Twitter disclosed it had 237.8 million daily users last July, four months before Mr. Musk bought the company and took it private.

Mr. Musk has taken action. On the same day last week that Threads was officially unveiled, Twitter threatened to sue Meta over the new app. On Sunday, Mr. Musk called Mr. Zuckerberg a “cuck” on Twitter. Then he challenged Mr. Zuckerberg to a contest to measure a specific body part and compare whose was larger, alongside an emoji of a ruler. Mr. Zuckerberg has not responded.

(Before Threads was announced, Mr. Musk separately dared Mr. Zuckerberg to fight a “cage match.”)

What Mr. Musk lacks at Twitter, Mr. Zuckerberg has in abundance at Meta: enormous audiences. More than three billion users regularly visit Mr. Zuckerberg’s constellation of apps, including Facebook, Instagram, WhatsApp and Messenger.

Mr. Zuckerberg has had plenty of experience nudging millions of people in those apps to use another of the apps. In 2014, for instance, he removed Facebook’s private messaging service from inside the social network’s app and forced people to download another app, called Messenger, to continue using the service.

Threads is now tied closely to Instagram. Users are required to have an Instagram account to sign up. People can import their entire following list from Instagram to Threads with just one tap of the screen, saving them from trying to find new people to follow on the service.

On Monday, Mr. Zuckerberg suggested there was more he could do to push Threads’ growth. He had not “turned on many promotions yet” for the app, he wrote in a Threads post.