Just a week after Bluesky, an open-source alternative to Twitter, opened its platform to the public, it has seen an enormous increase in users. Specifically, more than 850,000 new users, bringing the total number of logins to just over 4 million.

The service was in an invite-only beta for about a year, and at the time of its official opening to the public, it had just over 3 million users. It currently has nearly 4.1 million subscribed users, and the number continues to grow rapidly.

Bluesky CEO Jay Graber said Bluesky planned to grow at a slower pace so that it could build a platform and underlying protocol without the pressure that a sudden spike can cause. Some of these concerns were confirmed over the past day, when a surge in activity led to some technical issues on the site, including issues with the app’s own channels and a brief outage overnight. According to the company, the outage was resolved within a few hours.

Although Bluesky may look a bit like Threads or X, it is a completely different kind of platform and part of a growing movement for decentralized social media. Its open-source protocol works as an always-open API, according to Graber, and dozens of developers are already working on the site. Bluesky also offers users more customization options, such as custom algorithms and the ability to choose their own content moderation settings.

However, Bluesky’s future success will largely depend on whether it manages to sustain the growth and interest of all new users.