White paper: Impact of the Digital Choice Act on Social Media Services

Open protocol choices

/whitepapers/impact-digital-choice-act-on-social-media-services/open-protocol-choices/

At the time of this writing, there is no ready-made stack of protocols and formats that meets all of the requirements of the Digital Choice Act. However, there are several protocols that are good candidates to build with. We will discuss them in this section.

The ActivityPub stack

For the purposes of this paper, the “ActivityPub stack” refers to a set of official standards (from W3C and IETF) plus various community conventions that together make today’s ActivityPub-based Fediverse.

The ActivityPub stack defines a federated server-to-server architecture, with optional separate clients, in which independently operated websites exchange messages directly with each other, so that users on different websites can follow each other, react to each other’s content etc. All participating websites are peers to each other; there are no components in the architecture that have a special or globally unique role. There is no central party that has a global view into the system, and unless an SMS is either the originator of a message or the receiver, it has no access to the message.

The ActivityPub-based Fediverse today consists of:

tens of thousands independently operated SMS instances;
interoperating using the ActivityPub stack;
implemented in close to 100 code bases (including well-known ones such as Mastodon, Meta’s Threads, Pixelfed but many built by independent developers for their own projects);
with millions of users.

The ActivityPub stack is largely defined in the following standards and other documents:

ActivityPub. Christopher Webber; Jessica Tallon. W3C. 23 January 2018. W3C Recommendation. URL: https://www.w3.org/TR/activitypub/
Activity Streams 2.0. James Snell; Evan Prodromou. W3C. 23 May 2017. W3C Recommendation. URL: https://www.w3.org/TR/activitystreams-core/
ActivityPub and HTTP signatures. Ryan Barrett, nightpool. Draft Community Group Report. 03 August 2025. URL: https://swicg.github.io/activitypub-http-signature/
HTTP Signatures. Mark Cavage; Manu Sporny. IETF. 4 May 2013. W3C Working Draft. URL: https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures
ActivityPub and WebFinger. a, Evan Prodromou. Final Community Group Report. 21 October 2024. URL: https://swicg.github.io/activitypub-webfinger/
Data Portability in ActivityPub. Evan Prodromou. Draft Community Group Report. 15 July 2025. URL: https://swicg.github.io/activitypub-data-portability/
In addition, the community maintains extension proposals, called “Fediverse Enhancement Proposals” (FEPs), created and maintained by a variety of authors, at URL https://codeberg.org/fediverse/fep

Further standards development is ongoing, the Social Web working group at the W3C that created ActivityPub is currently in process of being re-chartered for updates to the ActivityPub stack.

The Bluesky / ATProto stack

At the time of this writing, the Bluesky / ATProto stack is being developed and documented primarily by Bluesky PBC, a venture capital-backed startup company spun out of Twitter. Bluesky PBC has announced their intention to bring the protocol to the IETF for possible standardizationWhile this process is being started, it remains at the very beginning and no predictions can be made at this time whether it will be successful or on what timeline. .

The Bluesky / ATProto architecture is centered around a global firehose (called “relay”), which conveys data elements created or updated by users in their own personal data stores to websites or other server-side applications (called “app views”) that aggregate and render certain types of data for users, and enables those users to create new records in their personal data stores. All data on the global firehose must be public.

The Bluesky / ATProto network today is dominated by Bluesky PBC. The company operates the vast majority of personal data stores, the default social media service built on ATProto used by most users, as well as the global firehose. However, independent developers are working on alternate software implementations of most components of the stack; some users are hosting their own personal data stores and some developers have started running complements or alternatives to the global firehose and app views.

Core documentation for the Bluesky / ATProto stack includes:

Authenticated Transfer: Architecture Overview. B. Newbold, D. Holmgren. IETF Internet Draft. 14 September 2025. URL: https://datatracker.ietf.org/doc/draft-newbold-at-architecture/
Authenticated Transfer Repository and Synchronization. D. Holmgren, B. Newbold. IETF Internet Draft. 14 September 2025. URL: https://datatracker.ietf.org/doc/draft-holmgren-at-repository/
ATProto website, containing ATProto documentation. URL: https://atproto.com

The Bluesky / ATProto stack is under active development. A number of independent developers are also developing extensions beyond what Bluesky PBC is developing.

The DSNP stack

«Proposed as candidate; need to research details»

Other candidates

We consider the following protocols and standards as less promising as a baseline to implement support for the Digital Choice Act, but we’d like to list them for completeness reasons: