Bluesky’s challenge to Elon Musk’s X is gaining momentum with nearly 5 million sign-ups

Early last week, the buzzy social network Bluesky—a onetime Twitter spinout that’s soaking up many refugees from the cesspit now known as X—finally started letting people in without invitations. And so far, the results are very encouraging for CEO Jay Graber and her roughly 40-strong team.

I had a chat with Graber yesterday, precisely a week after Bluesky flung open its doors. She said 1.5 million people had signed up in that time, adding to the 3.3 million who had already joined the platform—invited by other users—in the year or so since its test launch. That’s 45% growth. Not bad. Now comes the fun part.

This is a fascinating time in social networking, largely thanks to Elon Musk’s defilement of Twitter’s corpse. Mastodon, the long-running federation of decentralized social networks that are bound together with the ActivityPub protocol, is livelier than ever. Meta has created Threads and started testing its integration into the ActivityPub “fediverse.” But the most experimental action is happening over on Bluesky, now, as all those new users flood in.

Bluesky has a modular approach to federation—“one piece at a time,” as Graber puts it. Already, Bluesky has given people the ability to post their own curated timelines in the form of feeds that might specialize in, say, cats. There are now around 25,000 such feeds, which makes it easy for new users to quickly find and follow content that interests them.

Next week, the service will start to roll out data federation, allowing people to host their own data and identity if they want to. “One of our goals was to build a way to package all your data together so it’s always with you if you want to download it and keep a backup somewhere,” Graber said. As for why this might be useful … well, look at what just happened to members of the “queer.af” Mastodon instance, which got abruptly nuked by the Taliban (as we reported yesterday, this is because the .af top-level domain belongs to Afghanistan). “If something like that happened to your domain provider, [with Bluesky’s approach] you wouldn’t lose everything,” Graber claimed.

And in perhaps the wildest piece of federation experimentation, Bluesky will later this month start letting users create and offer their own moderation filters on the network, so users can choose whether they want their feeds to be filtered with a heavy or a light hand (there will be baseline standards of decency though, which Graber said would be roughly in line with those deployed at pre-Musk Twitter).

“We’re taking pieces of the social experience and handing them to third parties to run as they wish and create and develop on,” she said. (Incidentally, around half of Bluesky’s staff already work on support and/or moderation. Twenty people or less is not a lot of moderators when the user base is nearing 5 million, and I couldn’t get a clear answer about how many moderators are capable of handling non-English content—Bluesky is very big in Japan, for example.)

Why is Bluesky running with its own AT (Authenticated Transfer) protocol rather than ActivityPub? A bunch of reasons. A big one is ActivityPub’s aforementioned vulnerability to domain shutdowns. Another is the fact that, as Mastodon users will know well, discovering content across different ActivityPub services is a janky and limited experience.

“We wanted to give users control as well, but give them the option to participate in this global real-time firehose of information if they wanted to find out what’s happening on the other side of the world, or find all the posts on the network that contains cats,” Graber explained. “That required building something upfront that was very focused on discovery and data being public, and that’s something that the ActivityPub community still has a lot of resistance towards.”

So there’s a lot going on at Bluesky—and unlike Mastodon, users don’t have to get geeky if they just want a simple, Twitter-like experience. “It’s like we’ve built a lobby in a hotel where there’s many wings that branch off, but everyone can just come in the front door, have a good time if they want to stay in the lobby, and then there’s many more paths to explore if they want to go down another path,” Graber said.

Definitely one to watch—and if you do venture into Bluesky’s lobby, please say hi! More news below.

David Meyer

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This story was originally featured on Fortune.com