Stream agent responses

This guide shows you how to stream agent responses in real time using Server-Sent Events (SSE). You will learn about the two streaming endpoints, the SSE event format, and how to resume interrupted streams.

Prerequisites

An existing agent (see Create an agent)
An access token or client credentials
Understanding of the task lifecycle and A2A protocol

When to stream

Use streaming when you need real-time updates as the agent processes a message:

Showing incremental progress to users
Displaying partial results as they arrive
Monitoring long-running tasks

For simple request/response interactions, use message:send instead.

Stream a new message

Use message:stream to send a message and receive the response as an SSE stream:

# Replace these with your values
AGENT_ID="<your-agent-id>"
ENVIRONMENT="<eu-or-us>"
TENANT="<your-tenant-name>"
TOKEN="<your-access-token>"

curl -N -X POST "https://api.${ENVIRONMENT}.corti.app/v2/agentic/agents/${AGENT_ID}/a2a/message:stream" \
  -H "Authorization: Bearer ${TOKEN}" \
  -H "Tenant-Name: ${TENANT}" \
  -H "Content-Type: application/json" \
  -H "A2A-Version: 1.0" \
  -d '{
    "message": {
      "role": "ROLE_USER",
      "parts": [{ "text": "Generate a clinical note for this encounter." }]
    }
  }'

The -N flag disables cURL’s output buffering, which is necessary for receiving SSE events in real time.

SSE event format

Each event follows the W3C SSE wire format. The server currently sends only id and data lines. The event and retry fields are declared for forward compatibility but are not sent:

data: {"task":{"id":"task.0192f4c8-...","contextId":"ctx.0192f4c8-...","status":{"state":"TASK_STATE_WORKING","timestamp":"2026-05-19T12:00:00Z"}}}

data: {"artifactUpdate":{"taskId":"task.0192f4c8-...","contextId":"ctx.0192f4c8-...","artifact":{"artifactId":"art.0192f4c8-...","name":"clinical-note","parts":[{"text":"SOAP Note..."}]},"lastChunk":true}}

data: {"statusUpdate":{"taskId":"task.0192f4c8-...","contextId":"ctx.0192f4c8-...","status":{"state":"TASK_STATE_COMPLETED","timestamp":"2026-05-19T12:00:01Z"}}}

Event types

Each SSE event carries an A2AStreamResponse with exactly one field:

Field	Description
`task`	The full task object, sent when the task is created or state changes
`message`	A direct message response (no task lifecycle)
`statusUpdate`	Incremental status change (no `final` flag; clients infer finality from the task state)
`artifactUpdate`	Incremental artifact update with `lastChunk` flag

If you have a task ID (from a non-blocking message:send or after a stream dropped), use tasks:subscribe to stream updates:

TASK_ID="<your-task-id>"

curl -N -X POST "https://api.${ENVIRONMENT}.corti.app/v2/agentic/agents/${AGENT_ID}/a2a/tasks/${TASK_ID}:subscribe" \
  -H "Authorization: Bearer ${TOKEN}" \
  -H "Tenant-Name: ${TENANT}" \
  -H "A2A-Version: 1.0"

Resumption with Last-Event-ID

The server writes event IDs but does not yet read the Last-Event-ID request header, so resumption without gaps is not implemented. The section below describes the intended design for when this feature ships.

If an SSE stream drops, the intended resumption mechanism is to send the Last-Event-ID header with the most recent event ID you received:

LAST_EVENT_ID="event-123"

curl -N -X POST "https://api.${ENVIRONMENT}.corti.app/v2/agentic/agents/${AGENT_ID}/a2a/message:stream" \
  -H "Authorization: Bearer ${TOKEN}" \
  -H "Tenant-Name: ${TENANT}" \
  -H "Content-Type: application/json" \
  -H "A2A-Version: 1.0" \
  -H "Last-Event-ID: ${LAST_EVENT_ID}" \
  -d '{
    "message": {
      "role": "ROLE_USER",
      "parts": [{ "text": "Continue generating the note." }]
    }
  }'

The server will replay events from that point forward once the feature is implemented. This will work with both message:stream and tasks:subscribe.

Cancel a task

Cancel an in-flight task:

curl -X POST "https://api.${ENVIRONMENT}.corti.app/v2/agentic/agents/${AGENT_ID}/a2a/tasks/${TASK_ID}:cancel" \
  -H "Authorization: Bearer ${TOKEN}" \
  -H "Tenant-Name: ${TENANT}" \
  -H "A2A-Version: 1.0" \
  -H "Content-Type: application/json" \
  -d '{}'

The task transitions to TASK_STATE_CANCELED.

JSON-RPC streaming binding

You can also stream via the JSON-RPC binding by sending a message/stream method to the base A2A endpoint:

curl -N -X POST "https://api.${ENVIRONMENT}.corti.app/v2/agentic/agents/${AGENT_ID}/a2a" \
  -H "Authorization: Bearer ${TOKEN}" \
  -H "Tenant-Name: ${TENANT}" \
  -H "Content-Type: application/json" \
  -H "A2A-Version: 1.0" \
  -d '{
    "jsonrpc": "2.0",
    "id": "msg-001",
    "method": "SendStreamingMessage",
    "params": {
      "message": {
        "role": "ROLE_USER",
        "parts": [{ "text": "Generate a clinical note." }]
      }
    }
  }'

The SSE events carry JSON-RPC response envelopes instead of raw A2AStreamResponse objects.

Next steps

Read about the task lifecycle for state transitions
Learn how to send a message without streaming
Understand the A2A protocol bindings

Quickstart

Concepts

Guides

Reference

Registry Connectors

Agent SDK

v1 Documentation (archived)

Prerequisites

When to stream

Stream a new message

SSE event format

Event types

Resumption with Last-Event-ID

Cancel a task

JSON-RPC streaming binding

Next steps

​Prerequisites

​When to stream

​Stream a new message

​SSE event format

​Event types

​Subscribe to an existing task

​Resumption with Last-Event-ID

​Cancel a task

​JSON-RPC streaming binding

​Next steps

Prerequisites

When to stream

Stream a new message

SSE event format

Event types

Subscribe to an existing task

Resumption with Last-Event-ID

Cancel a task

JSON-RPC streaming binding

Next steps