X does not share its total user numbers but it is understood to be measured in the hundreds of millions.
Bluesky was started by Twitter co-founder Jack Dorsey in 2019. The platform announced this week it had surpassed 19 million users.
Despite helping fund and start it, Mr Dorsey is no longer part of the team behind the social network.
The key difference between Bluesky and most other social media platforms is that it is decentralised, meaning it is operated on independent servers and not those owned by the company.
It describes itself as “social media as it should be” – a place where people can come together over shared interests “and have some fun again”.
Many new users have said their decision to join Bluesky was driven by Elon Musk, who heavily backed Donald Trump’s election campaign and intends to remain involved in the new administration.
Last week, the Guardian announced it will no longer post on X, saying the US election underlined its concerns that Musk had been able to use X to “shape political discourse”.
