Data: Managed Agents events and steering

Managed Agents — Events & Steering

Events

Sending Events

Send events to a session via POST /v1/sessions/{id}/events.

Receiving Events

Three methods:

1. Streaming (SSE): GET /v1/sessions/{id}/events/stream — real-time Server-Sent Events. Long-lived — the server sends periodic heartbeats to keep the connection alive.
2. Polling: GET /v1/sessions/{id}/events — paginated event list (query params: limit default 1000, page). Returns immediately — this is a plain paginated GET, not a long-poll.
3. Webhooks: Anthropic POSTs session state transitions to your HTTPS endpoint — thin payloads (IDs only), HMAC-signed, Console-registered. See shared/managed-agents-webhooks.md.

All received events carry id, type, and processed_at (ISO 8601; null if not yet processed by the agent).

⚠️ Robust polling (raw HTTP). If you bypass the SDK and roll your own poll loop, don't rely on requests or httpx timeouts as wall-clock caps — they're per-chunk read timeouts, reset every time a byte arrives. A trickling response (heartbeats, a wedged chunked-encoding body, a misbehaving proxy) can keep the call blocked indefinitely even with timeout=(5, 60) or httpx.Timeout(120). Neither library has a "total wall-clock" timeout built in. For a hard deadline: track time.monotonic() at the loop level and break/cancel if a single request exceeds your budget (e.g. via a watchdog thread, or asyncio.wait_for() around async httpx). Prefer the SDK — client.beta.sessions.events.stream() and client.beta.sessions.events.list() handle timeout + retry sanely.

If GET /v1/sessions/{id}/events (paginated) ever hangs after headers, you've likely hit GET /v1/sessions/{id}/events by mistake or a server-side stall — report it; don't treat it as a client-config problem.

Event Types (Received)

Event types use dot notation, grouped by namespace:

The stream also echoes back user-sent events (user.message, user.interrupt, user.tool_confirmation, user.custom_tool_result, user.define_outcome).

Steering Patterns

Practical patterns for driving a session via the events surface.

Stream-first ordering

Open the stream before sending events. The stream only delivers events that occur after it's opened — it does not replay current state or historical events. If you send a message first and open the stream second, early events (including fast status transitions) arrive buffered in a single batch and you lose the ability to react to them in real time.

// ✅ Correct — stream and send concurrently
const [response] = await Promise.all([
  streamEvents(sessionId),   // opens SSE connection
  sendMessage(sessionId, text),
]);

// ❌ Wrong — events before stream opens arrive as a single buffered batch
await sendMessage(sessionId, text);
const response = await streamEvents(sessionId);

For full history, use GET /v1/sessions/{id}/events (paginated list) — the stream only gives you live events from connection onward.

Reconnecting after a dropped stream

The SSE stream has no replay. If your connection drops (httpx read timeout, network blip) and you reconnect, you only get events emitted after reconnection. Any events emitted during the gap are lost from the stream.

The consolidation pattern: on every (re)connect, overlap the stream with a history fetch and dedupe by event ID:

def connect_with_consolidation(client, session_id):
    # 1. Open the SSE stream first
    stream = client.beta.sessions.events.stream(session_id=session_id)

    # 2. Fetch history to cover any gap
    history = client.beta.sessions.events.list(
        session_id=session_id,
    )

    # 3. Yield history first, then stream — dedupe by event.id
    seen = set()
    for ev in history.data:
        seen.add(ev.id)
        yield ev
    for ev in stream:
        if ev.id not in seen:
            seen.add(ev.id)
            yield ev

Message queuing

You don't have to wait for a response before sending the next message. User events are queued server-side and processed in order. This is useful for chat bridges where the user sends rapid follow-ups:

// All three go into one session; agent processes them in order
await sendMessage(sessionId, "Summarize the README");
await sendMessage(sessionId, "Actually also check the CONTRIBUTING guide");
await sendMessage(sessionId, "And compare the two");
// Stream once — agent responds to all three as a coherent turn

Events can be sent up to the Session at any time. There is no need to wait on a specific session status to enqueue new events via client.beta.sessions.events.send()

Interrupt

An interrupt event jumps the queue (ahead of any pending user messages) and forces the session into idle. Use this for "stop" / "nevermind" / "cancel" commands:

await client.beta.sessions.events.send(sessionId, {
  events: [{ type: 'interrupt' }],
});

The agent stops mid-task. It does not see the interrupt as a message — it just halts. Send a follow-up user event to explain what to do instead. If an outcome is active, the interrupt also marks span.outcome_evaluation_end.result: "interrupted" (see shared/managed-agents-outcomes.md).

Note: Interrupt events may have empty IDs in the current implementation. When troubleshooting, use the processed_at timestamp along with surrounding event IDs.

Event payloads

some events carry useful metadata beyond the status change itself:

session.status_idle — includes a stop_reason field which elaborates on why the session stopped and what type of further action is required by the user.

{
  "id": "sevt_456",
  "processed_at": "2026-04-07T04:27:43.197Z",
  "stop_reason": {
    "event_ids": [
      "sevt_123"
    ],
    "type": "requires_action"
  },
  "type": "status_idle"
}

span.model_request_end contains a model_usage field for cost tracking and efficiency analysis:

{
  "type": "span.model_request_end",
  "id": "sevt_456",
  "is_error": false,
  "model_request_start_id": "sevt_123",
  "model_usage": {
    "cache_creation_input_tokens": 0,
    "cache_read_input_tokens": 6656,
    "input_tokens": 3571,
    "output_tokens": 727
  },
  "processed_at": "2026-04-07T04:11:32.189Z"
}

agent.thread_context_compacted — emitted when the conversation history was summarized to fit context. Includes pre_compaction_tokens so you know how much was squeezed:

{
  "id": "sevt_abc123",
  "processed_at": "2026-03-24T14:05:15.787Z",
  "type": "agent.thread_context_compacted"
}

Archive

When done with a session, archive it to free resources:

await client.beta.sessions.archive(sessionId);

Archiving a session is routine cleanup — sessions are per-run and disposable. Do not generalize this to agents or environments: those are persistent, reusable resources, and archiving them is permanent (no unarchive; new sessions cannot reference them). See shared/managed-agents-overview.md → Common Pitfalls.