AGTP Session Protocol

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Table of Contents

1. Introduction

Base AGTP defines request-and-response semantics for individual method invocations between agents. Many real-world agent interactions span multiple invocations under shared context: a chatbot conversation that continues across hours, an agentic commerce flow that completes a transaction across a sequence of methods, a research agent maintaining working state across a long-running task.¶

These interactions need session semantics that base AGTP does not specify. AGTP-SESSION defines those semantics as a companion protocol that builds on base AGTP without modifying it.¶

The architectural commitment is straightforward: a session in AGTP is an agent-level abstraction. It is not a TLS connection, a QUIC connection, or a transport-layer session. It is a logical context shared between two or more agents (or between an agent and an API), within which multiple method invocations carry shared identity, authority scope, and attribution chain.¶

A session may map to a single underlying transport connection, may span multiple connections over time, or may persist while the underlying transport is intermittently disconnected and reestablished. The session state is the agent-level fact; the connection is the mechanism that carries traffic when active.¶

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

Session:

A logical context shared between AGTP participants under which multiple method invocations are correlated, identity and authority remain consistent, and shared state evolves across the lifetime of the session. Sessions are agent-level abstractions, not transport- level constructs.¶

Bounded Session:

A session with an explicit termination condition: a time limit, an action completion, or a transaction outcome. Bounded sessions are appropriate for commerce flows, multi-step delegations with finite scope, and any agent interaction with a defined end state.¶

Persistent Session:

A long-lived session intended to span hours, days, or longer. State is maintained across reconnections. Persistent sessions are appropriate for chatbot interactions, research agents, monitoring agents, and other contexts where the agent retains continuity.¶

Session Identifier:

A unique identifier assigned at session establishment that is carried in every method invocation within the session. Format and scope of session identifiers are TBD.¶

Session Context:

The shared state associated with a session, including (but not limited to) participant Agent-IDs, Authority-Scope grants applicable to the session, accumulated Attribution-Records for invocations within the session, and any session-specific governance metadata.¶

3. Session Models

AGTP-SESSION defines two session models. Implementations MAY support one or both depending on deployment profile.¶

4. Session Establishment

A session is established explicitly via an ESTABLISH method invoked between two AGTP participants. Implicit establishment via an extended- context flag on a standard method invocation is noted as an alternative under consideration but is NOT RECOMMENDED as the primary mechanism. Explicit establishment provides:¶

• Unambiguous negotiation of session model (bounded or persistent), session lifetime, and any session-scoped Authority-Scope grants¶

• A clear root for the session attribution chain, with the ESTABLISH invocation serving as the first signed Attribution-Record under the session¶

• Clean error semantics when negotiation fails (e.g., 451 Scope Violation if session-scoped grants exceed the establishing agent's Authority-Scope, 4xx for unsupported session models, 5xx for governance platform unavailability)¶

• Predictable enforcement boundaries for governance platforms and Scope-Enforcement Points, which can recognize session establishment as a distinct event rather than inferring it from method context¶

The full wire format and parameter set for ESTABLISH is not specified in this version. At minimum, the method MUST carry:¶

• The proposed session model (bounded or persistent)¶

• A proposed session lifetime (session_ttl) for bounded sessions¶

• Any session-scoped Authority-Scope grants the establishing agent proposes for the session context¶

• Standard AGTP request fields (Agent-ID, Principal-ID, Authority- Scope, signature)¶

A successful ESTABLISH response MUST carry:¶

• A session identifier (format TBD; see Open Questions)¶

• The accepted session model and lifetime¶

• The accepted Authority-Scope grants for the session¶

• A governance platform signature binding the session identifier to the participating Agent-IDs¶

Rejection of an ESTABLISH request follows base AGTP status code semantics. Implementations MUST NOT establish a session by side effect of any other method invocation; the absence of a successful ESTABLISH response means no session exists.¶

5. Inheritance from Base AGTP

AGTP-SESSION inherits all base AGTP properties:¶

• Agent-only at the wire level. Sessions exist between agents, not between general-purpose actors.¶

• Agent-ID and Principal-ID present on every method invocation, including invocations within a session.¶

• Authority-Scope enforced on every method invocation. Scopes are not relaxed inside sessions.¶

• Attribution Records signed for every invocation, including those within sessions, with the session identifier included in the attribution metadata.¶

• Status codes, including 451 Scope Violation and 551 Authority Chain Broken, apply within sessions exactly as outside them.¶

• Three-level verification model. Sessions do not weaken verification.¶

AGTP-SESSION adds session-specific semantics on top of these properties; it does not replace or modify them.¶

6. Transport Considerations

Base AGTP runs over TCP with TLS 1.3 or over QUIC. AGTP-SESSION inherits these transport options.¶

QUIC is a particularly natural fit for persistent sessions because of its connection migration capability [RFC9000], which allows a logical connection to survive IP address changes and network path changes without renegotiation. AGTP-SESSION over QUIC can leverage QUIC's connection migration to maintain a persistent session across network transitions transparently.¶

7. Relationship to MOQT and Real-Time Media

The proposed AI Agent Communication Protocols (acp) charter under discussion at IETF anticipates a session protocol on webtransport or MOQ as a foundational building block for agent communication. That work and AGTP-SESSION reflect inverse architectural commitments.¶

The acp approach treats session and transport semantics as the foundation, with agent-specific concerns (identity, authority, attribution) layered on top by the protocols that compose on the session. Under this model, the session protocol does not know that its traffic is agent traffic; agent semantics are an application- layer concern.¶

AGTP-SESSION reflects the inverse: agent-specific concerns are the foundation (in base AGTP), and session semantics layer on top of an agent-aware substrate. Under this model, a session is, by definition, an agent session. The protocol carries identity, authority, and attribution at the wire level for every method invocation within the session, because the substrate beneath the session already commits to carrying agent traffic structurally.¶

The two architectures are not mutually exclusive in deployment. MOQT-style relay-based pub/sub patterns and real-time media streaming address use cases (particularly voice with sub-100ms barge-time interruption) that AGTP-SESSION does not currently address. A future companion draft (or a later version of AGTP-SESSION) may define how AGTP composes with MOQT-style transport for real-time agent media, or how MOQT-style sessions can carry AGTP semantic envelopes.¶

The architectural choice between these two foundations is a question for community discussion. Both deliver session semantics; they differ on which layer commits to knowing the traffic is agent traffic.¶

8. Application Layering: Voice and Multi-Modal Agents

AGTP-SESSION focuses on session semantics for agent communication. It does not specify protocols for real-time voice, video, or multi-modal data exchange.¶

Voice agents, video agents, and multi-modal agents are application- layer constructs that can compose on top of AGTP and AGTP-SESSION. They are not different kinds of agents at the protocol layer; they are agents that produce or consume specific media types.¶

This raises a related architectural question worth surfacing for community discussion: AGTP may benefit from an agent type system, analogous to HTTP Content-Type, that allows the protocol to identify the kind of agent or kind of agent payload involved in a given exchange. This is not part of AGTP-SESSION as currently scoped but is flagged here as adjacent work that may warrant its own companion specification.¶

9. Out of Scope for v00

The following are deliberately out of scope for this version:¶

• Real-time voice and barge-time interruption semantics¶

• Pub/sub and relay-based session patterns (MOQT-style multicast)¶

• Session migration across organizations or governance platforms¶

• Session state synchronization across multiple agents in a chain¶

• Detailed protocol specification for ESTABLISH/OPEN methods¶

• Session encryption beyond what TLS 1.3 or QUIC already provides¶

• Wire format for session metadata¶

These are flagged as future work or as open questions to be resolved through community input.¶

10. Security Considerations

Base AGTP security considerations apply to every method invocation within a session, including invocations occurring under bounded or persistent session models. This section identifies session-specific risks and mitigations that supplement the base AGTP threat model.¶

11. IANA Considerations

TBD.¶

12. References

Appendix A. Open Questions

• Should sessions be established explicitly via an ESTABLISH method, or implicitly via an extended-context flag on a standard method?¶

• What is the canonical format and scope for session identifiers? (256-bit similar to Agent-ID, or shorter for performance?)¶

• How does session attribution interact with the base AGTP Attribution-Record? Are session-level attribution rollups defined?¶

• How are persistent sessions migrated across governance platform changes (e.g., merchant changes governance providers mid-session)?¶

• Should AGTP define an agent type system (Agent Content-Type) separately, or as part of session establishment?¶

• What is the right composition story with MOQT for real-time agent media use cases?¶

• Should multi-party sessions (more than two participants) be in scope for this draft, or deferred to a separate companion?¶

Appendix B. Contributors

This draft is informed by the IETF agent2agent charter formation discussion and by feedback on the architectural layering question raised in that thread.¶

Author's Address