Threads will also use ActivityPub, adding a significant boost to that project and introducing the biggest player yet to the scene. A handful of other sites also already allow ActivityPub integration, including the blogging site WordPress.com and the content curation site Flipboard.

“Threads is really the biggest commercial network that has connected to this universe by far,” said Evan Prodromou, an ActivityPub co-author. “It’s really exciting. My guess is that this is going to be a gradual process, that they’re going to be doing this over weeks and months. It’s not going to be all today.”

The fediverse is still tiny compared to Threads, with about 11 million users, the vast majority of them on Mastodon. While Meta has not yet broken out Threads users in its public filings, Zuckerberg said the platform reached 100 million users in its first five days in July. That growth appears to have since cooled, and data from December has shown its activity has dropped off somewhat.

But there is growth on the horizon. Zuckerberg said Thursday that Threads would open to more European countries. That announcement comes as X, formerly Twitter, faces potential legal fallout in Europe, which has much stricter rules for large social media platforms than the United States. In October, European Union regulators said they’re investigating X for allegedly being a hub of disinformation surrounding the Israel-Hamas war. On Thursday, a European activist sued X, alleging it violated E.U. privacy laws.

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Zuckerberg described the integration with ActivityPub as “a test” but didn’t offer a clear timeline for the integration. Meta didn’t respond to a request for clarification.

Adam Mosseri, head of Instagram, wrote on Threads that the platform is starting with the ability to follow Threads users from other ActivityPub platforms, adding that the ability for Threads users to follow accounts from other platforms is in the works.

If Threads goes through with full ActivityPub integration, people will be able to follow Threads users and see their posts without having to join the platform (Threads currently forces users to sign up through an Instagram account). Similarly, Threads users will be able to follow users and see posts from across ActivityPub’s network.

“The network effect for ActivityPub is gaining some serious momentum right now,” Mike McCue, co-founder and CEO of the newsreader Flipboard, posted on Threads. “As more services adopt the protocol, more people, more communities and more content are added to the network making it increasingly more valuable for everyone. This will only accelerate in the coming months as Threads, WordPress, Tumblr, Flipboard and others federate.”

A widespread fediverse would still likely face significant challenges in large part due to its decentralized nature. Moderation becomes much more complicated among platforms, and disinformation and misinformation will likely be hard to tackle. Mozilla, the tech-focused nonprofit group behind the Firefox web browser, has already launched an effort to see what content moderation could look like in the fediverse.

Christine Lemmer-Webber, an ActivityPub co-author and co-editor, said she was excited about Threads joining the fediverse but had reservations about a tech giant suddenly dominating the technology. Meta, because of its size, could start dictating how the network operates.

In such a scenario, Meta would “come in, hook up to the system, and then say, ‘Well, we’re the biggest player really. Actually you all have to do it our way or the highway,’” she said.