A transport-agnostic wire protocol for submitting, observing, and controlling long-running AI agent jobs.

Current draft: v1 — Standards Track — expires November 13, 2026

ARCP defines the durable execution envelope around AI agent work: sessions, jobs, resumable event streams, capability-bounded leases, and delegation. It stays agnostic about agent implementation and tool transport — MCP exposes tools, OpenTelemetry handles telemetry export, and ARCP composes with both.

Four concerns, scoped tightly:

• Identity — who is talking, what session, what trace
• Durability — resumable streams, gap-free sequencing, idempotent submission
• Authority — leases over filesystem, network, tools, sub-agents, and cost
• Observability — structured events, progress, metrics, streamed results

• Sessions — authenticated, resumable, with capability negotiation in session.hello / session.welcome
• Liveness — explicit session.ping / session.pong heartbeats (§6.4)
• Flow control — session.ack for window-based event acknowledgement (§6.5)
• Introspection — session.list_jobs for read-only job inventory (§6.6)
• Idempotent submission — idempotency_key on job.submit for safe retries
• Subscription — job.subscribe to attach to a running job from a different session, without inheriting cancel authority (§7.6)
• Agent versioning — name@version identifiers with inventory advertised in session.welcome (§7.5)
• Leases — capability-bounded authority over fs.*, net.fetch, tool.call, agent.delegate
• Time-bounded authority — lease_constraints.expires_at (§9.5)
• Budget enforcement — cost.budget capability with runtime-maintained counters and per-currency tracking (§9.6)
• Delegation — sub-agent jobs with strict lease subsetting (§10)
• Progress reporting — structured progress events (§8.2)
• Result streaming — result_chunk events for large outputs (§8.4)
• Trace propagation — W3C Trace Context across sessions, jobs, and delegations (§11)
• Fifteen-code error taxonomy — including BUDGET_EXHAUSTED, LEASE_EXPIRED, AGENT_VERSION_NOT_AVAILABLE (§12)

Out of scope, deliberately:

• Agent implementation
• Tool exposure (use MCP)
• HITL UX
• Agent state persistence across process restarts
• Telemetry export (use OpenTelemetry)
• Auth mechanisms beyond bearer tokens
• Scheduling, priority, federation, pause/resume, LLM token streaming — deferred

Eleven first-party SDKs track the same spec version. Pick the one closest to your stack.

The full draft lives in SPEC.md.

Draft specification distributed for review. Implementations are encouraged but should expect breaking changes before v1 is finalized. The wire format is the contract — anything not specified here is implementation-defined.

Capability negotiation is the forward-compatibility story: both peers advertise a features list in session.hello / session.welcome, and the effective feature set is their intersection. New features land behind new flags so older clients keep working.

Issues and pull requests welcome. For protocol-level changes, open an issue first to discuss intent before sending a PR — once a feature flag ships in a registered implementation it is effectively frozen.

When proposing changes, please indicate:

1. Which section(s) are affected
2. Whether the change is backward-compatible with the feature-negotiation rules in §6.2
3. Whether it introduces a new feature flag, error code, event kind, or capability namespace (these require IANA-registry coordination per §15)

[TBD]