The ongoing Twitter exodus sparked life into a new way of doing social media. Instead of a handful of platforms trying to control your life online, people are reclaiming control by building more open and empowering approaches to social media. Some of these you may have heard of: Mastodon, Bluesky, and Threads. Each is distinct, but their differences can be hard to understand as they’re rooted in their different technical approaches. 

The mainstream social web arguably became “five websites, each consisting of screenshots of text from the other four,”  but in just the last few years radical and controversial changes to major platforms were a wake up call to many and are driving people to seek alternatives to the billionaire-driven monocultures.

Two major ecosystems have emerged in the wake, both encouraging the variety and experimentation of the earlier web. The first, built on ActivityPub protocol, is called the Fediverse. While it includes many different kinds of websites, Mastodon and Threads have taken off as alternatives for Twitter that use this protocol. The other is the AT Protocol, powering the Twitter alternative Bluesky.

These protocols, a shared language between computer systems, allow websites to exchange information. It’s a simple concept you’re benefiting from right now, as protocols enable you to read this post in your choice of app or browser. Opening this freedom to social media has a huge impact, letting everyone send and receive posts their own preferred way. Even better, these systems are open to experiment and can cater to every niche, while still connecting to everyone in the wider network. You can leave the dead malls of platform capitalism, and find the services which cater to you.

To save you some trial and error, we have outlined some differences between these options and what that might mean for them down the road.

ActivityPub and AT Protocols


The Fediverse goes a bit further back,  but ActivityPub’s development by the world wide web consortium (W3C) started in 2014. The W3C is a public-interest non-profit organization which has played a vital role in developing open international standards which define the internet, like HTML and CSS (for better or worse). Their commitment to ActivityPub gives some assurance the protocol will be developed in a stable and ostensibly consensus driven process.

This protocol requires a host website (often called an “instance”) to maintain an “inbox” and “outbox” of content for all of its users, and selectively share this with other host websites on behalf of the users. In this federation model users are accountable to their instance, and instances are accountable to each other. Misbehaving users are banned from instances, and misbehaving instances are cut off from others through “defederation.” This creates some stakes for maintaining good behavior, for users and moderators alike.

ActivityPub handles a wide variety of uses, but the application most associated with the protocol is Mastodon. However, ActivityPub is also integral to Meta’s own Twitter alternative, Threads, which is taking small steps to connect with the Fediverse. Threads is a totally different application, solely hosted by Meta, and is ten times bigger than the Fediverse and Bluesky networks combinedmaking it the 500-pound gorilla in the room. Meta’s poor reputation on privacy, moderation, and censorship, has driven many Fediverse instances to vow they’ll defederate from Threads. Other instances still may connect with Threads to help users find a broader audience, and perhaps help sway Threads users to try Mastodon instead.

AT Protocol

The Authenticated Transfer (AT) Protocol is newer; sparked by Twitter co-founder Jack Dorsey in 2019. Like ActivityPub, it is also an open source protocol. However, it is developed unilaterally by a private for-profit corporation— Bluesky PBLLC— though it may be imparted to a web standards body in the future. Bluesky remains mostly centralized. While it has recently opened up to small hosts, there are still some restrictions preventing major alternatives from participating. As developers further loosens control we will likely see rapid changes in how people use the network.

The AT Protocol network design doesn’t put the same emphasis on individual hosts as the Fediverse does, and breaks up hosting, distribution, and curation into distinct services. It’s easiest to understand in comparison to traditional web hosting. Your information, like posts and profiles, are held in Personal Data Servers (PDSes)—analogous to the hosting of a personal website. This content is then fetched by relay servers, like web crawlers, which aggregate a “firehose” of everyone’s content without much alteration. To sort and filter this on behalf of the user, like a “search engine,” AT has Appview services, which give users control over what they see. When accessing the Appview through a client app or website, the user has many options to further filter, sort, and curate their feed, as well as “subscribe” to filters and labels someone else made.

The result is a decentralized system which can be highly tailored while still offering global reach. However, this atomized system also may mean the community accountability encouraged by the host-centered system may be missing, and users are ultimately responsible for their own experience and moderation. This will depend on how the network opens to major hosts other than the Bluesky corporation.

User Experience

Mastodon, Threads and Bluesky have a number of differences that are not essential to their underlying protocol which affect users looking to get involved today. Mastodon and Bluesky are very customizable, so these differences are just addressing the prevalent trends.

Timeline Algorithm

Most Mastodon and most ActivityPub sites prefer a more straightforward timeline of content from accounts you follow. Threads have a Meta-controlled algorithm, like Instagram. Bluesky defaults to a chronological feed, but opens algorithmic curation and filtering up to apps and users. 

User Design

All three services present a default appearance that will be familiar to anyone who has used Twitter. Both Mastodon and Bluesky have alternative clients with the only limit being a developer’s imagination. In fact, thanks to their open nature, projects like SkyBridge let users of one network use apps built for the other (in this case, Bluesky users using Mastodon apps). Threads does not have any alternate clients and requires a developer API, which is still in beta.


Threads has the greatest advantage to getting people to sign up, as it has only one site which accepts an Instagram account as a login. Bluesky also has only one major option for signing up, but has some inherent flexibility in moving your account later on. That said, diving into a few extra setup steps can improve the experience. Finally, one could easily join Mastodon by joining the flagship instance, However, given the importance of choosing the right instance, you may miss out on some of the benefits of the Fediverse and want to move your account later on. 


Threads has a reputation for being more brand-focused, with more commercial accounts and celebrities, and Meta has made no secret about their decisions to deemphasize political posts on the platform. Bluesky is often compared to early Twitter, with a casual tone and a focus on engaging with friends. Mastodon draws more people looking for community online, especially around shared interests, and each instance will have distinct norms.

Privacy Considerations

Neither ActivityPub nor AT Protocol currently support private end-to-end encrypted messages at this time, so they should not be used for sensitive information. For all services here, the majority of content on your profile will be accessible from the public web. That said, Mastodon, Threads, and Bluesky differ in how they handle user data.


Everything you do as a user is entrusted to the instance host including posts, interactions, DMs, settings, and more. This means the owner of your instance can access this information, and is responsible for defending it against attackers and law enforcement. Tech-savvy people may choose to self-host, but users generally need to find an instance run by someone they trust.

The Fediverse muffles content sharing through a myriad of permissions set by users and instances. If your instance blocks a poorly moderated instance for example, the people on that other site will no longer be in your timelines nor able to follow your posts. You can also limit how messages are shared to further reduce the intended audience. While this can create a sense of community and closeness,  remember it is still public and instance hosts are always part of the equation. Direct messages, for example, will be accessible to your host and the host of the recipient.

If content needs to be changed or deleted after being shared, your instance can request these changes, and this is often honored. That said, once something is shared to the network, it may be difficult to “undo.”


All user content is entrusted to one host, in this case Meta, with a privacy policy similar to Instagram. Meta determines when information is shared with law enforcement, how it is used for advertising, how well protected it is from a breach, and so on.

Sharing with instances works differently for Threads, as Meta has more restricted interoperability. Currently, content sharing is one-way: Threads users can opt-in to sharing their content with the Fediverse, but won’t see likes or replies. By the end of this year, they will allow Threads users to follow accounts on Mastodon accounts.

Federation on Threads may always be restricted, and features like transferring one's account to Mastodon may never be supported. Limits in sharing should not be confused with enhanced privacy or security, however. Public posts are just that—public—and you are still trusting your host (Meta) with private data like DMs (currently handled by Instagram). Instead these restrictions, should they persist, should be seen as the minimum level of control over users Meta deems necessary.


Bluesky, in contrast, is a very “loud” system. Every public message, interaction, follow and block is hosted by your PDS and freely shared to everyone in the network. Every public post is for everyone and is only discovered according to their own app and filter preferences. There are ways to algorithmically imitate smaller spaces with filtering and algorithmic feeds, such as with the Blacksky project, but these are open to everyone and your posts will not be restricted to that curated space.

Direct messages are limited to the flagship Bluesky app, and can be accessed by the Bluesky moderation team. The project plans to eventually incorporate DMs into the protocol, and include end-to-end-encryption, but it is not currently supported. Deletion on Bluesky is simply handled by removing the content from your PDS, but once a message is shared to Relay and Appview services it may remain in circulation a while longer according to their retention settings.



Mastodon’s approach to moderation is often compared to subreddits, where the administrators of an instance are responsible for creating a set of rules and empowering a team of moderators to keep the community healthy. The result is a lot more variety in moderation experience, with the only boundary being an instance’s reputation in the broader Fediverse. Instances coordinating and “defederating” from problematic hosts has already been effective in the Fediverse. One former instance, Gab, was successfully cut off from the Fediverse for hosting extreme right-wing hate. The threat of defederation sets a baseline of behavior across the Fediverse, and from there users can choose instances based on reputation and on how aligned the hosts are with their own moderation preferences.

At its best, instances prioritize things other than growth. New members are welcomed and onboarded carefully as new community members, and hosts only grow the community if their moderation team can support it. Some instances even set a permanent cap on participation to a few thousand to ensure a quality and intimate experience. Current members too can vote with their feet, and if needed split off into their own new instance without needing to disconnect entirely.

While Mastodon has a lot going for it by giving users a choiceavoiding automation, and avoiding unsustainable growth, there are other evergreen moderation issues at play. Decisions can be arbitrary, inconsistent, and come with little recourse. These aren't just decisions impacting individual users, but also those affecting large swaths of them, when it comes to defederation. 


Threads, as alluded to when discussing privacy above, aims for a moderation approach more aligned with pre-2022 Twitter and Meta’s other current platforms like Instagram. That is, an impossible task of scaling moderation with endless growth of users.

As the largest of these services however, this puts Meta in a position to set norms around moderation as it enters the Fediverse. A challenge for decentralized projects will be to ensure Meta’s size doesn’t make them the ultimate authority on moderation decisions, a pattern of re-centralization we’ve seen happen in email. Spam detection tools have created an environment where email, though an open standard, is in practice dominated by Microsoft and Google as smaller services are frequently marked as spammers. A similar dynamic could play out with the federated social web, where Meta has capacity to exclude smaller instances with little recourse. Other instances may copy these decisions or fear not to do so, lest they are also excluded. 


While in beta, Bluesky received a lot of praise and criticism for its moderation. However, up until recently, all moderation was handled by the centralized Bluesky company—not throughout the distributed AT network. The true nature of moderation structure on the network is only now being tested.

AT Protocol relies on labeling services, aka “labelers”  for moderation. These special accounts using Bluesky’s Ozone tool labels posts with small pieces of metadata. You can also filter accounts with account block lists published by other users, a lot like the Block Together tool formerly available on Twitter. Your Appview aggregating your feed uses these labels to and block lists to filter content. Arbitrary and irreconcilable moderation decisions are still a problem, as are some of the risks of using automated moderation, but it is less impactful as users are not deplatformed and remain accessible to people with different moderation settings. This also means problematic users don’t go anywhere and can still follow you, they are just less visible.

The AT network is censorship resistant, and conversely, it is difficult to meaningfully ban users. To be propagated in the network one only needs a PDS to host their account, and at least one Relay to spread that information. Currently Relays sit out of moderation, only scanning to restrict CSAM. In theory Relays could be more like a Fediverse instance and more accurately curate and moderate users. Even then, as long as one Relay carries the user they will be part of the network. PDSes, much like web hosts, may also choose to remove controversial users, but even in those cases PDSes are easy to self-host even on a low-power computer.

Like the internet generally, removing content relies on the fragility of those targeted. With enough resources and support, a voice will remain online. Without user-driven approaches to limit or deplatform content (like defederation), Bluesky services may be targeted by censorship on the infrastructure level, like on the ISP level.

Hosting and Censorship

With any internet service, there are some legal obligations when hosting user generated content. No matter the size, hosts may need to contend with DMCA takedowns, warrants for user data, cyber attacks,  blocking from authoritarian regimes, and other pressures from powerful interests. This decentralized approach to social media also relies on a shared legal protection for all hosts, Section 230.  By ensuring they are not held liable for user-generated content, this law provides the legal protection necessary for these platforms to operate and innovate.

Given the differences in the size of hosts and their approach to moderation, it isn’t surprising that each of these platforms will address platform liability and censorship differently.


Instance hosts, even for small communities, need to navigate these legal considerations as we outlined in our Fediverse legal primer. We have already seen some old patterns reemerge with these smaller, and often hobbyist, hosts struggling to defend themselves from legal challenges and security threats. While larger hosts have resources to defend against these threats, an advantage of the decentralized model is censors need to play whack-a-mole in a large network where messages flow freely across the globe. Together, the Fediverse is set up to be quite good at keeping information safe from censorship, but individual users and accounts are very susceptible to targeted censorship efforts and will struggle with rebuilding their presence.


Threads is the easiest to address, as Meta is already several platforms deep into addressing liability and speech concerns, and have the resources to do so. Unlike Mastodon or Bluesky, they also need to do so on a much larger scale with a larger target on their back as the biggest platform backed by a multi-billion dollar company. The unique challenge for Threads however will be how Meta decides to handle content from the rest of the Fediverse. Threads users will also need to navigate the perks and pitfalls of sticking with a major host with a spotty track record on censorship and disinformation.


Bluesky is not yet tested beyond the flagship Bluesky services, and raises a lot more questions. PDSes, Relays and even Appviews play some role in hosting, and can be used with some redundancies. For example your account on one PDS may be targeted, but the system is designed to be easy for users to change this host, self-host, or have multiple hosts while retaining one identity on the network.

Relays, in contrast, are more computationally demanding and may remain the most “centralized” service as natural monopolies— users have some incentive to mostly follow the biggest relays. The result is a potential bottle-neck susceptible to influence and censorship. However, if we see a wide variety of relays with different incentives, it becomes more likely that messages can be shared throughout the network despite censorship attempts.

You Might Not Have to Choose

With this overview, you can start diving into one of these new Twitter alternatives leading the way in a more free social web. Thanks to the open nature of these new systems, where you set up will become less important with improved interoperability.

Both ActivityPub and AT Protocol developers are receptive to making the two better at communicating with one another, and independent projects like  Bridgy Fed, SkyBridge, RSS Parrot and Mastofeed are already letting users get the best of both worlds. Today a growing number of projects speak both protocols, along with older ones like RSS. It may be these paths towards a decentralized web become increasingly trivial as they converge, despite some early growing pains. Or the two may be eclipsed by yet another option. But their shared trajectory is moving us towards a more free, more open and refreshingly weird social web free of platform gatekeepers.