More than 10 million people have signed up to Threads, Meta’s rival to Twitter, within the first few hours of its launch, the Facebook parent’s CEO Mark Zuckerberg said Thursday.

Threads is the biggest challenger yet to Elon Musk-owned Twitter, which has seen a series of potential competitors emerge but not yet replace one of social media’s most iconic companies, despite its epic struggles.

The app went live on Apple and Android app stores in 100 countries at 2300 GMT on Wednesday, and will run with no ads for now.

“10 million sign ups in seven hours,” Zuckerberg wrote on his official Threads account Thursday.

Accounts were already active for celebrities such as Jennifer Lopez, Shakira and Hugh Jackman, as well as media outlets including The Washington Post and The Economist.

Zuckerberg spent the first few hours of the platform’s launch replying to new users.

“One thing that’s up is the number of world champion MMA fighters on Threads, especially now that you’re here!” he wrote in a reply to American MMA fighter Jon Jones.

“Round one of this thing is getting off to a good start,” he said in another.

Zuckerberg also offered a shot across the bow at Musk — the pair are known to be bitter rivals, and have even offered to meet each other in a fighting cage to wrestle it out.

In his first tweet in over a decade, Zuckerberg posted a Spiderman pointing at Spiderman meme in an apparent reference to the similarity of the two platforms.

Back on Threads, he wrote: “It’ll take some time, but I think there should be a public conversations app with 1 billion+ people on it. Twitter has had the opportunity to do this but hasn’t nailed it. Hopefully we will.”

Twitter has said it has more than 200 million daily users.

Threads was introduced as a clear spin-off of Instagram, which offers a built-in audience of more than two billion users, thereby sparing the new platform the challenge of starting from scratch.

Zuckerberg is widely understood to be taking advantage of Musk’s chaotic ownership of Twitter to push out the new product, which Meta hopes will become the go-to communication channel for celebrities, companies and politicians.

“It’s as simple as that: if an Instagram user with a large number of followers such as Kardashian or a Bieber or a Messi begins posting on Threads regularly, a new platform could quickly thrive,” strategic financial analyst Brian Wieser said on Substack.

Analyst Jasmine Engberg from Insider Intelligence said Threads only needs one out of four Instagram monthly users “to make it as big as Twitter.”

“Twitter users are desperate for an alternative, and Musk has given Zuckerberg an opening,” she added.

Instagram chief Adam Mosseri told users that Threads was intended to build “an open and friendly platform for conversations.”

“The best thing you can do if you want that too is be kind,” he said.

Under Musk, Twitter has seen content moderation reduced to a minimum with glitches and rash decisions scaring away celebrities and major advertisers.

Musk hired advertising executive Linda Yaccarino to steady the ship, but she has not been spared his whimsy.

The Tesla tycoon said last week that he was limiting access to Twitter to ward off AI companies from “scraping” the site to train their technology.

Musk then angered Twitter’s most devoted aficionados by declaring that access to its TweetDeck product — which allows users to view a fast flow of tweets at once — would be for paying customers only.

Meta has its legion of critics too, especially in Europe, and despite Instagram’s massive user base, they could slow the site’s development.

The company is criticized mainly for its handling of personal data — the essential ingredient for targeted ads that help it rake in billions of dollars in profits every quarter.

Mosseri said he regretted that the EU launch was delayed, but if Meta had waited for regulatory clarity from Brussels, Threads would remain “many, many, many, months away.”

“I was worried that our window would close, because timing is important,” he added to Platformer, a tech news site.

According to a source close to the matter, Meta was wary of a new law called the Digital Markets Act (DMA), which sets strict rules for the world’s “gatekeeper” internet companies.

One rule restricts platforms from transferring personal data between products, as would potentially be the case between Threads and Instagram.

Meta was caught out for doing just that after it bought the messaging app WhatsApp, and European regulators will be on high alert to ensure that the company doesn’t do so illegally with Threads.

Globally, the Threads hashtag on Twitter has garnered over a million tweets, with many users jokingly suggesting users would be returning to Twitter.

“10 mins into threads app. Me coming back to Twitter,” one user wrote, sharing a video of a man sprinting.

Another shared an image of Homer Simpson running back and forth between the Twitter and Threads logos.

By midday local time Thursday, Threads was the top trending topic on Japan Twitter, but many users expressed concerns over data privacy.

“Threads is run by Meta, isn’t it? It will definitely leak your real name or the game you are playing, or put you in the list of your workplace company friends,” wrote one user.

Another said: “Meta loves to collect private information and I don’t trust the way it treats private information. I also have the impression that this is a company hated by EU, so I’m reluctant.”