Meta’s Twitter rival, Threads, logged five million sign-ups in its first four hours of operation, according to CEO Mark Zuckerberg, as the company seeks to woo users from Elon Musk’s troubled platform through an offer of lengthier posts, a handful of celebrity backers – and a strong resemblance to its competitor.

The Facebook and Instagram owner brought forward the app’s debut by 15 hours to 7pm EDT in the US and midnight in the UK, making it freely available in 100 countries on the Apple and Google app stores, although regulatory concerns mean it will not be available in the EU.

Brands such as Billboard, HBO, NPR and Netflix, and even us here at Business Matters had accounts set up within minutes of launch. Meta said initial celebrity backers included Shakira and Gordon Ramsay, with a recent report suggesting that Oprah Winfrey and the Dalai Lama had also been approached.

Thread users will need an Instagram account to log in. Once they have signed up, they can choose to follow the same accounts they follow on Instagram, if they too have joined the new app.

The app closely resembles Twitter visually, although some of the wording has been changed, with retweets called “reposts” and tweets called “threads”. Meta has not been averse to copying rival products in the past, including the 2020 launch of Instagram’s Reels feature, noted for its similarity to TikTok’s short-form videos.

Posts on Threads can be 500 characters long, compared with 280 for most Twitter users, and videos of up to five minutes in length can be posted while a post can be shared as a link on other platforms. Users can unfollow, block, restrict or report others. Users can also filter out replies with certain words in them.

Meta has launched Threads in the wake of another turbulent period at Twitter, which imposed tweet viewing limits at the weekend in a move it blamed partly on data harvesting by companies building artificial intelligence models.

In subsequent Threads posts, Zuckerberg addressed those challenges. “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,” he wrote.

Reaction to the debut on Wednesday ranged from caution to enthusiasm, many praising its ease of use and some saying that Elon Musk should be worried. Others pointed out the app’s speedy integration with Instagram showed just how powerful Meta has become. Much of the conversation, ironically, took place on Twitter, where the hashtag “Threads” was trending on Wednesday evening.

News of Zuckerberg’s impending unveiling of Threads had resulted in the Facebook founder and Musk apparently agreeing to a cage fight over the matter, although a date has not been set for the unlikely confrontation.

Meta described Threads as a “new, separate space for real-time updates and public conversations”, aiming to “take what Instagram does best and expand that to text, creating a positive and creative space to express your ideas”. Twitter has a user base of more than 250 million, while Instagram reportedly has 2 billion users.

Meta said the app would also resemble Twitter’s rivals such as Mastodon, which is based on a decentralised platform that would allow accounts to be transferred to other services. It said: “We are working toward making Threads compatible with the open, interoperable social networks that we believe can shape the future of the internet.”

Meta said it was planning to make Threads compatible with ActivityPub, technology that also underpins Mastodon and allows social networks to be interoperable, which would let users of Threads take their accounts and followers to other ActivityPub-supported apps.

Meta said users could stop using the Threads app and transfer their content to another service that uses the same underlying technology – such as Mastodon. “Our vision is that people using compatible apps will be able to follow and interact with people on Threads without having a Threads account, and vice versa, ushering in a new era of diverse and interconnected networks.” As with Mastodon, Meta envisages mini-communities forming with their own community standards and moderation policies.

Currently, the main feed is a mixture of content that users follow, as well as content recommended from the algorithm. There are currently no plans to allow people to limit that to only people they follow. People will keep their usernames from Instagram, reducing the possibility of people name-squatting high profile usernames.

Mindful of criticism from politicians and campaigners over the safety of children on its platform, Meta is defaulting every UK Threads user under 18 to a private profile that can only be viewed by people the user approves.

Mike Proulx, research director at the analysis firm Forrester, said Threads was “yet another” copycat move but had been launched at a time of “peak Twitter frustration”, although the marketplace for rivalling Twitter was already flooded with alternatives such as Hive, Bluesky and Mastodon. “This only serves to fracture the Twitter alternative-seeking user base,” he said.