---
title: Streaming events
---
# Streaming events
Server-Sent Events (SSE) streamed when using `stream: true` in the request. This page is a quick overview of the most common events — for the **complete** event catalog with every payload field, see the [Streaming Event Object](./streaming-event-object.md) reference.
The stream always ends with a terminal `data: [DONE]` line.
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## Event Types
**`response.created`**
Sent when the response is created and processing begins.
Show data structure
**`thread_id`** string required
The thread ID.
**`status`** string required
Always `in_progress`.
**`is_summarized`** boolean optional
Whether the conversation history was summarized.
**`output_mode`** string optional
Echoes the requested output mode.
Example:
```json
{"thread_id":"thrd_xyz789","status":"in_progress","is_summarized":false,"output_mode":"text"}
```
**`response.content_delta`**
Sent for each text chunk as it's generated.
Show data structure
**`delta`** string required
The text chunk being streamed.
Example:
```json
{"delta":"Hello"}
```
**`response.tool.started`** / **`response.tool.done`**
Sent when a tool/connector invocation begins and finishes. Tool blocks may include an optional `icon_url` string field with the tool's brand icon URL.
Show data structure
Example:
```json
{"event":"response.tool.done","id":"call_paris_weather","type":"mcp_tool","name":"get_weather","status":"completed","success":true,"execution_time_ms":245,"result":"{\"temperature\":15,\"condition\":\"Partly Cloudy\"}"}
```
**`response.reasoning.started`**
Sent when reasoning content starts streaming.
**`response.reasoning.delta`**
Sent for each reasoning chunk as it's generated.
Show data structure
**`delta`** string required
The reasoning chunk being streamed.
Example:
```json
{"event":"response.reasoning.delta","delta":"I should call get_weather with city=Paris."}
```
**`response.reasoning.completed`**
Sent when reasoning content streaming is complete.
**`response.completed`**
Sent when the entire response is complete.
Show data structure
**`status`** string required
Always `completed`.
Example:
```json
{"status":"completed","thread_id":"thrd_xyz789","response_id":"resp_abc123","stop_reason":"end_turn","response":[{"type":"text","text":"Hello"}]}
```
**`response.error`**
Sent if the response fails.
Show data structure
**`status`** string required
Always `failed`.
**`message`** string required
Error message.
Example:
```json
{"status":"failed","message":"Rate limit exceeded"}
```
## Usage
These events are streamed by:
- [Create a model response](../responses/create.md) - When `stream: true` is set
For the full set of streamed events (content, tools, web search, knowledge search, images, skins, skills, tasks, and provider passthrough), see the [Streaming Event Object](./streaming-event-object.md) reference.
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