The Agent Trust Handshake Protocol uses semantic version identifiers following the format MAJOR.MINOR (e.g., 0.1, 0.2, 1.0).

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Version Scheme

ComponentMeaning
Major (e.g., 1.x)Breaking changes to the protocol interface
Minor (e.g., 0.2)New features, backward-compatible additions
The protocol version will not be incremented for backward-compatible changes. This allows incremental improvements while preserving interoperability between implementations targeting the same major version.

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Current Version

The current protocol version is v0.1, which covers:
  • Agent identity model (URI-based Agent_ID + signed JWT attestation)
  • Three discovery modes (manual, gateway catalog, service-side .well-known)
  • Trusted handshake flow (Phase A: agent registration, Phase B: user OAuth consent)
  • PKCE (RFC 7636) and Resource Indicators (RFC 8707)
  • Scope intersection enforcement
  • API endpoints (register, authorize, token, proxy, revoke)
  • Security considerations

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Discovery Document Versioning

The ath_version field in discovery documents (/.well-known/ath.json and /.well-known/ath-app.json) indicates which protocol version the implementation supports: 
{
  "ath_version": "0.1",
  ...
}
Agents SHOULD check this field to ensure compatibility before proceeding with registration.

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Planned Versions

See the Roadmap for details on planned protocol versions.