The Bluesky social network has risen in popularity recently with one million new daily sign-ups in the past week.
It has become a serious rival to Elon Musk's X (formerly Twitter), which it resembles in colour and branding.
The Hollywood Reporter reported that it hit 20 million users on Tuesday.
X reportedly had 588 million users as of September.
Treasury Minister Darren Jones and former Labour leader Jeremy Corbyn are among the British politicians who have created Bluesky accounts.
But Prime Minister Sir Keir Starmer has no plans “at the moment” to create a personal or official UK Government account in his name.
Jack Dorsey, a co-founder of Twitter, founded Bluesky in 2019.
But Mr Dorsey left its board of directors in May 2024. He deleted his Bluesky account in September.
He said Bluesky's shift toward a traditional corporate structure and the introduction of centralised moderation tools influenced his leaving. He added that Bluesky was "repeating all mistakes" Twitter made.
Bluesky is now a US public benefit corporation primarily owned and operated by CEO Jay Graber.
But who is she?
Here’s all you need to know.
Who is Jay Graber?
Jay Graber is a prominent software engineer, entrepreneur, and decentralised social media advocate.