ATproto
Federated Protocol
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License MIT / Apache 2.0 (dual license for patent assurance); github.com/bluesky-social/atproto (TypeScript reference); github.com/bluesky-social/indigo (Go BGS/Relay)
Dev Status 🟢 Active
Dev Status Detail Released (production; Bluesky app with 20M+ users; Internet Drafts submitted to IETF September 2025 for repository and sync specs; IETF working group charter published January 2026; OAuth deployed to network)
Owner Bluesky Social PBC (CEO: Jay Graber, CTO: Paul Frazee); originally funded by Jack Dorsey/Twitter; IETF working group charter published January 2026 for standardization
Country USA (Seattle)
Start Year 2019
Stack TypeScript (reference PDS implementation); Go (BGS/Relay, indigo); Lexicon (JSON-based schema definition language, similar to JSON Schema/OpenAPI)
Funding Twitter/Block grant (initial $13M); VC funding ($8M Series A 2023, $15M 2024 = $23M+ after Twitter split)
Last Investigated Jan 15, 2026
Federated Protocol Attributes
Origins Social networking (decentralized Twitter alternative; addresses perceived issues with ActivityPub and Nostr including UX, semantic interoperability, discoverability, scalability, and data portability)
Database Repository (signed Merkle Search Tree / DAG) + AppView databases for indexing; CBOR-encoded records; CIDs for content addressing
Query Language XRPC (HTTP-based RPC protocol) + Lexicon schemas (define structure of data records, API endpoints, and event stream messages; DNS-like lookup for lexicon resolution)
Data Formats CBOR (DAG-CBOR for repositories and records) + JSON (API responses); borrows formats from IPFS ecosystem (IPLD, CID) but does not use IPFS network
Collaborative Live Editing N/A (designed for social posts and records; not collaborative editing)
Rich Text Editing Application-level (Bluesky supports rich text facets — mentions, links, tags as byte-range annotations)
Mobile Support Yes (Bluesky official apps for iOS/Android; third-party apps like Graysky, Skeets)
Web Support Yes (Bluesky web app at bsky.app; third-party web clients)
Native Apps Yes (iOS, Android; third-party desktop clients; independent apps like Blacksky, Leaflet)
Terms Self-hosting (PDS) + Free public PDS (bsky.social operated by Bluesky) + Third-party PDS hosting
Funds $23M+ in VC funding (post-Twitter split; Bluesky Social PBC)
Based On IPLD data structures (CID, DAG-CBOR); DID standards (did:plc custom method + did:web); OAuth 2.0/OIDC for authentication; does not use IPFS network despite borrowing formats
Content Addressing Yes (CIDs for blobs and repo commits; content-addressed via IPLD/CID format; self-authenticating data verifiable from any copy)
E2EE Not yet implemented (planned as 'entire second phase of protocol development'; encompasses private accounts, direct messages, encrypted data; MLS being explored; recommended against 'bolting on' encryption with existing primitives)
Signature DID-based signatures (K-256/secp256k1 elliptic curve for repository signing; all repo commits cryptographically signed; self-authenticating — data integrity verifiable from any copy without trusting source server)
Permissions DID-based + Lexicon-defined permissions; OAuth 2.0 scopes for client authorization (deployed to network); Labelers for content classification; atproto-native scopes system integrating with Lexicons under development
Semantic Web Compatibility N/A (custom schema language 'Lexicon' — not RDF; Lexicons are JSON-based schema definitions similar to JSON Schema or OpenAPI; provide semantic interoperability within ATproto ecosystem)
Federation Model Shared-heap via Relay: PDS (Personal Data Servers) host user repositories; Relay/BGS (Big Graph Service) aggregates global firehose of all repo events; AppViews index and serve application-specific APIs; modular microservice architecture separating data hosting, aggregation, and application logic
Instance / Server Requirements PDS: Low (~1GB RAM, modest hardware); Relay/BGS: High (resource-intensive global indexing of entire network); AppView: Moderate to high (application-dependent)
Account Portability Full portability (DID-based identity; can migrate between PDS providers; designed for account migration even with non-cooperative PDS; social graph survives migration because DIDs are server-independent; some migration details still being finalized)
Discovery / Relay Architecture Global Relay (BGS firehose — aggregates all PDS events via WebSocket streams) + AppViews for application-specific indexing/search + Labelers for content classification; DNS-like lexicon resolution for schema discovery
Server Authority Model Minimal server authority (PDS stores user data but doesn't control identity; Relay is unopinionated indexer; AppView filters and curates; user can move PDS without losing identity or social graph; Labelers provide moderation without controlling speech)
Protocol Maturity / Standardization Proprietary open standard transitioning to IETF: Internet Drafts for repository format and data sync submitted September 2025; IETF working group charter published January 2026; additional specs (schemas, identity, OAuth, private data) under development by Bluesky PBC
Data Sovereignty User-controlled via PDS (Personal Data Server); self-authenticating data (signed Merkle trees verifiable independent of hosting server); users own their repositories and can verify data integrity without trusting PDS