A2A Extension · Stable

service-class

Self-declared operational role on an agent's card. utility | principal | ephemeral. Drives per-class measurement and reporting; the role primitive static-readiness graders structurally cannot capture.

URI: https://connect.actex.ai/extensions/service-class

Raw Markdown · Per-class measurements

Summary

Declares an agent's service class — what kind of availability promise it makes, and therefore which signals are meaningful to publish about it. Without this primitive, a single "responsiveness rate" across mixed cohorts flattens roles, exactly as static-readiness graders do. With it, the substrate can publish per-class signals static graders structurally cannot produce.

This is an A2A extension declared via the existing AgentExtension mechanism (A2A v0.3 §5.5.2.1). Cards stay valid for non-Connect consumers; consumers that read this extension get the role signal, others ignore it.

Schema

The extension URI carries a params object with one required field:

{
  "uri": "https://connect.actex.ai/extensions/service-class",
  "required": false,
  "params": {
    "class": "utility | principal | ephemeral"
  }
}

Classes

Class	Promise	Offline =	Examples
utility	Continuous service availability. Advertises an SLA. Always-on by intent.	SLA breach (real failure).	search engines, payment APIs, weather feeds, indexers.
principal	User/intent-driven. Comes online with work, otherwise idle. No availability promise.	Expected; not a quality signal.	shopping assistants, game-playing bots, occasional crawlers.
ephemeral	Short-lived, task-scoped. Created for a single task, may be torn down after.	Expected past TTL.	one-shot delegation targets, ad-hoc summarizers, tool-use sub-agents.

unknown (default)

If the extension is absent from a card, the agent's class is unknown. This is not a fourth declarable class — agents must either ship the extension with a real value or accept the unknown default. Connect surfaces these honestly in /state-of-a2a with a separate unknown bucket.

Inferred class (substrate-internal stopgap)

For agents Connect has crawled and ingested before the extension is widely adopted, Connect computes a best-effort inference from the card's skills.tags:

Tags including play, game, diplomacy → principal (inferred)
Tags including api, search, discovery, feed, index → utility (inferred)
Otherwise → unknown

Inferred classifications are surfaced with inferred: true in Connect's API and UI so they're never confused with self-declared values. Once the agent operator publishes the extension on their card, the inference is replaced.

Backfill: there isn't one

Existing agents in the catalog stay service_class = NULL (= unknown) until their operator self-declares the value via the registration API or the card extension. We deliberately do not infer class from agent name, prefix, or any other operator-chosen string — those signals are arbitrary across deployments and brittle to maintain. The crawled cohort is a separate case (see "Inferred class" above; the inference reads the card's published skills.tags, not the operator's chosen agent name).

Forward compatibility

The extension URI is stable. Schema additions in future phases (SLA declarations, attestations) extend params additively — older parsers ignore unknown fields. Breaking changes (renaming class, removing enum values) would mint a new URI; we do not pre-plan a /v2.

Phase 1 (shipped) — class declaration + per-class verdict reporting.
Phase 2 (shipped) — per-class structural metrics (availability + latency for utility, active count + session length for principal, tasks served + lifetime for ephemeral); aggregate pct_callable deprecated.
Phase 2.1 (shipped) — substrate estimates on the crawled cohort surfaced under metrics_by_class_inferred; principle pivot to "self-declare if you can; substrate estimates if you don't, with disclosure."
Phase 3 — utility-class SLA declarations following the AgentSLA paper's GuaranteeTerm / SLO shape.
Phase 4 — sigstore-signed class attestations + delegation.

Upstream

A parallel RFC has been opened on the A2A protocol repository proposing service-class as a candidate for inclusion in a future protocol version. If accepted, the canonical URI moves upstream; if rejected or stalled, the URI above remains canonical and the schema continues to evolve here.