It is the most successful launch in the history of technological applications, surpassing the ChatGPT application, the chatbot based on artificial intelligence.
ChatGPT reached 100 million users in two months, while TikTok did it in nine months.
Instagram, launched in 2010, took two and a half years to reach that number.
Threads is available in the Apple and Android app stores in more than 100 countries since Wednesday, although not in the European Union, where the giant Meta (parent company of Facebook and Instagram), maintains differences with the authorities on the right to data protection.
Twitter has about 200 million users, according to observer estimates.
Bought by billionaire Elon Musk last year, the network has suffered technical mishaps.
Musk fired thousands of Twitter employees after the controversy that erupted in the United States, where the company maintained close contacts with the authorities to combat false news.
The eccentric billionaire also created controversy by imposing payments on Twitter users for services that were previously free.
Although competitors have already sprung up trying to take advantage of the turmoil, none have succeeded in dethroning Twitter.
With Meta’s muscle, Threads begins to break records
Threads, on the other hand, is a serious rival because it takes advantage of the huge user base of Instagram, regularly used by more than a billion people.
According to online monitoring service Quiver Quantitative, Threads surpassed 100 million users as of 0700 GMT on Monday.
Other sites calculate that the application could exceed that number before, based on the downloads detected among Instagram users.
Threads uses a Twitter-like interface, and Musk has threatened to sue Meta for alleged intellectual property theft.
Musk recently challenged Meta boss Mark Zuckerberg to a fight, who assured that he accepted the challenge.