The upstart social network has been by invitation only since its launch last year

“I didn’t see the future,” Graber said in an interview Monday, referring to the subsequent ouster of Dorsey as Twitter’s CEO and sale of the company to Elon Musk. “But as I like to say, the captain can always sink the ship.”

Today, Bluesky is opening to the public after nearly a year as an invitation-only app, with Graber as its CEO. With a little over 3 million users, it’s mounting a long-shot bid to take on the company that spawned it — and to set social media on a course that no single captain can control.

On the surface, Bluesky looks familiar to anyone who has used Twitter or Meta’s Threads, with a feed full of text posts and images from people you follow. Underneath, however, the company is building what Graber calls “an open, decentralized protocol” — a software system that allows developers and users to create their own versions of the social network, with their own rules and algorithms. She compared the idea to email, where users of different apps like Gmail, Outlook and Yahoo Mail can interact freely because they all run on the same underlying technology.

That system is a work in progress. So far, Bluesky is the only social network using its protocol. But it already has some features that set it apart.

For instance, users can subscribe to feeds where algorithms prioritize the most popular posts overall or the posts most popular among the people they follow. There are also options for feeds geared to their specific areas of interest, such as science or art. And users can toggle personal moderation settings that either “hide,” “warn” or “show” categories of content such as nudity, violence, spam and hate-group iconography.

Along with today’s public launch of Bluesky, the company said it will roll out in the coming weeks a step toward its broader vision, inviting some outside developers to host servers that plug in to the main Bluesky network. It also announced a new feature that will let users and organizations begin todevelop their own content moderation services, which other users can then subscribe to. For instance, a fact-checking organization could apply “false” or “misleading” labels to certain posts, which would then be seen by users who opt in to seeing them.

The idea of a decentralized social media system is similar to that behind Mastodon, a seven-year-old nonprofit that relies on individual users and organizations to host and moderate their own, sometimes insular corners of its network. But Bluesky said its protocol would work differently, letting users customize their experience but keeping the network fundamentally public.

First launched on iOS in February 2023, Bluesky quickly surged in popularity among users disenchanted with Musk’s Twitter. Savvy social media users begged one another for “invite codes” to join the fledgling network, whose quirky first adopters gave it a vibe that some likened to the early days of Twitter. Vibrant communities sprang up around art, transgender identity and media, drawing large pockets of users in Brazil and Japan as well as the United States.

But with fewer than a dozen employees at the time, Graber put off a public launch, fearing that it would force the company to spend all its resources on maintaining and moderating the Bluesky network rather than building out the underlying “decentralized” system.

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In the meantime, social media behemoth Meta launched Threads, which has rocketed to 130 million monthly active users in just seven months, according to the company’s latest earnings report. In a call with investors last week, Meta CEO Mark Zuckerberg said it’s “on track, I think, to be a major success.”

X has more than half a billion monthly active users, CEO Linda Yaccarino said last fall, though apples-to-apples comparisons are difficult because X does not regularly report industry-standard metrics.

Rose Wang, who oversees operations and strategy for Bluesky, said its goal is to combine the ease of use and shared experience of closed platforms like X and Threads with the user choice and openness of systems like Mastodon’s. With Mastodon, which requires you to select and join one of thousands of differently managed servers before you can participate, “there’s almost too much user choice,” Wang said. “You don’t understand what you’re joining.”

For Bluesky, which now has a few dozen employees, mounting a serious challenge to X or Threads would be an uphill battle. Some of the early enthusiasm appears to have waned, with high-profile users such as Chrissy Teigen and Rep. Alexandria Ocasio-Cortez (D-N.Y.) going dormant or leaving the platform after making headlines when they joined last year. Even Dorsey, who remains a Bluesky board member, appears no longer to have an active account.

A page that tracks user statistics on Bluesky shows that the number of users actively posting each day has dipped slightly over the past month.

Still, at a time when the content moderation decisions of tech’s giants routinely alienate swaths of users, Wang said she’s optimistic the company’s choose-your-own-adventure approach will have enduring appeal.

“Lots of people want a different experience that’s not something run by Mark Zuckerberg or another billionaire,” she said. “I don’t think we’re going to go back to a world where there’s only one microblogging client like Twitter.”

Mike Masnick, editor of the blog Techdirt and a longtime tech analyst, has followed Bluesky’s progress from the start, after a paper he wrote helped to inspire Dorsey to create the project. “They’re doing a lot of smart things that give me hope,” he said of Graber and her team. “I think it could carve out a successful space even if it doesn’t beat Threads.”

Instagram CEO Adam Mosseri, who runs Threads, has said he also hopes to eventually make it interoperable with federated protocols such as Mastodon’s. But Threads so far has only tested limited versions of that functionality.

Amy Zhang, a professor at University of Washington’s Allen School of Computer Science & Engineering, has been researching Bluesky to study how users respond when given options to control their feeds and moderation systems. Whether Bluesky takes off, she said she’s interested to see whether other platforms adopt some of the features it’s pioneering.

“This idea that there’s one algorithm for everybody’s feeds — that there’s one moderation setting for millions of people — it’s kind of impossible, and it doesn’t fit a lot of people’s needs,” Zhang said.

Naomi Nix contributed to this report.