Threads went live on Apple and Android app stores in 100 countries late on Wednesday, though it is not available in Europe due to legal issues the parent company Meta has had with the European Union’s data privacy legislation.
Twitter is thought to have around 200 million regular users but it has suffered repeated technical failures since Elon Musk bought the platform last year and sacked thousands of staff.
Musk, who also serves as the boss of Tesla and SpaceX, has also alienated many users by introducing charges for previously free services and allowing banned right-wing accounts back on the platform.
Several rivals have emerged, but most are niche platforms without the capacity to grow at the necessary scale to dethrone Twitter.
Threads is finding it easier because it is linked to Instagram, which has more than one billion regular users.
Online data service Quiver Quantitative reported that the app passed 100 million users at 07:00 GMT on Monday.
Other websites using a count of the “badges” received by Instagram users who have downloaded Threads reckoned the mark had been passed earlier.
