Bluesky, the open source Twitter alternative, has seen a surge in new users just one day after opening its platform up to the public. The service has gained more than 850,000 users bringing its total sign-ups to just over 4 million.

The service had been in an invitation-only beta for about a year and had grown to just over 3 million users when it officially opened to the public. It currently has close to 4.1 million sign-ups, according to an online tracker. “Things are rolling over here,” Bluesky CEO Jay Graber wrote in a post on X.

The surge in new users suggests that there is still ample curiosity about the Jack Dorsey-backed platform that began as an internal project at Twitter in 2019. It also indicated that Meta hasn’t entirely cornered the market for a text-based Twitter alternative. The company’s Threads app has grown to 130 million monthly users, Meta announced last week.

Graber has said that Bluesky intended to grow at a slower pace so that it could build it the platform, and the underlying protocol, without the added pressure sudden surges in growth can cause. Some of those concerns were borne out over the last day as the spike in activity led to some technical issues on the site, including problems with the app’s custom feeds and a brief outage overnight. The outage was resolved within a couple hours, according to the company.

Much of Bluesky’s future success will hinge on whether it can maintain new growth and keep the interest of all its new users. Threads also saw an initial spike in new users, only for it to drop-off before eventually rebounding.

Though Bluesky may look a bit like Threads or X, it’s a fundamentally different kind of platform and part of the growing movement for decentralized social media. Its open-source protocol functions like a “permanently open” API, according to Graber, and the site already has dozens of developers building their own experiences. Bluesky also offers more customization features for users, with features like custom algorithms and the ability to choose your own content moderation settings.

Threads is beginning to test a bookmarking feature to allow users to save posts, according to Instagram head Adam Mosseri. The update is beginning as a “limited test,” but the “heavily requested” feature will eventually have a permanent place on the service, the company said.

According to screenshots shared by Meta, the “save” button on Threads will look very similar to Instagram’s version of the feature. Users will be able to access their bookmarked posts from the “save” section of the app’s settings.

While the ability to save posts may not seem like the most exciting update, it will help bring a little more organization to the app. threads currently lacks direct messaging, search filtering, lists and a number of other features often requested by power users looking to replace the functionality of Twitter (now known as X).

Threads recently introduced searchable tags, but Meta has so far resisted adding chronological search or trending features. Mosseri has said chronological search could be easily gamed by spammers, though an “internal prototype” of the feature was recently spotted in the wild. Meta employees have also been spotted sharing images of a feature that looks a lot like trending topics, though it’s unclear what the company’s plans for it may be.

In a statement, a Meta spokesperson said the company “will continue listening to community feedback for ways to improve the Threads experience.” The app has climbed to 130 million monthly users, Mark Zuckerberg revealed last week. He has said that the app has the potential to be the company’s next billion-user service.