Implementation:Openai Openai python Response Stream Event

Knowledge Sources	Openai_Openai_python OpenAI API Reference
Domains	API_Types, Responses_API
Last Updated	2026-02-15 00:00 GMT

Overview

Concrete discriminated union type alias representing all possible streaming events from the Responses API, provided by the openai-python SDK.

Description

ResponseStreamEvent is a TypeAlias defined as an Annotated[Union[...]] of over 40 distinct event types, discriminated on the type field via PropertyInfo(discriminator="type"). This union covers every event that can be emitted during a streaming response, including lifecycle events (created, in_progress, completed, failed, incomplete, queued), content events (text delta/done, audio delta/done, refusal delta/done), reasoning events (reasoning text delta/done, reasoning summary text delta/done, reasoning summary part added/done), tool call events (function call, web search, file search, code interpreter, image generation, MCP, custom tool), and annotation events.

Usage

Import this type when you need a single type annotation that encompasses all possible streaming events, for example when typing a generic event handler function.

Code Reference

Source Location

• Repository: openai-python
• File: src/openai/types/responses/response_stream_event.py

Signature

ResponseStreamEvent: TypeAlias = Annotated[
    Union[
        ResponseAudioDeltaEvent,
        ResponseAudioDoneEvent,
        ResponseAudioTranscriptDeltaEvent,
        ResponseAudioTranscriptDoneEvent,
        ResponseCodeInterpreterCallCodeDeltaEvent,
        ResponseCodeInterpreterCallCodeDoneEvent,
        ResponseCodeInterpreterCallCompletedEvent,
        ResponseCodeInterpreterCallInProgressEvent,
        ResponseCodeInterpreterCallInterpretingEvent,
        ResponseCompletedEvent,
        ResponseContentPartAddedEvent,
        ResponseContentPartDoneEvent,
        ResponseCreatedEvent,
        ResponseErrorEvent,
        ResponseFileSearchCallCompletedEvent,
        ResponseFileSearchCallInProgressEvent,
        ResponseFileSearchCallSearchingEvent,
        ResponseFunctionCallArgumentsDeltaEvent,
        ResponseFunctionCallArgumentsDoneEvent,
        ResponseInProgressEvent,
        ResponseFailedEvent,
        ResponseIncompleteEvent,
        ResponseOutputItemAddedEvent,
        ResponseOutputItemDoneEvent,
        ResponseReasoningSummaryPartAddedEvent,
        ResponseReasoningSummaryPartDoneEvent,
        ResponseReasoningSummaryTextDeltaEvent,
        ResponseReasoningSummaryTextDoneEvent,
        ResponseReasoningTextDeltaEvent,
        ResponseReasoningTextDoneEvent,
        ResponseRefusalDeltaEvent,
        ResponseRefusalDoneEvent,
        ResponseTextDeltaEvent,
        ResponseTextDoneEvent,
        ResponseWebSearchCallCompletedEvent,
        ResponseWebSearchCallInProgressEvent,
        ResponseWebSearchCallSearchingEvent,
        ResponseImageGenCallCompletedEvent,
        ResponseImageGenCallGeneratingEvent,
        ResponseImageGenCallInProgressEvent,
        ResponseImageGenCallPartialImageEvent,
        ResponseMcpCallArgumentsDeltaEvent,
        ResponseMcpCallArgumentsDoneEvent,
        ResponseMcpCallCompletedEvent,
        ResponseMcpCallFailedEvent,
        ResponseMcpCallInProgressEvent,
        ResponseMcpListToolsCompletedEvent,
        ResponseMcpListToolsFailedEvent,
        ResponseMcpListToolsInProgressEvent,
        ResponseOutputTextAnnotationAddedEvent,
        ResponseQueuedEvent,
        ResponseCustomToolCallInputDeltaEvent,
        ResponseCustomToolCallInputDoneEvent,
    ],
    PropertyInfo(discriminator="type"),
]

Import

from openai.types.responses import ResponseStreamEvent

I/O Contract

Fields

Name	Type	Required	Description
(discriminator)	type field on each variant	Yes	Each union member has a unique literal type value used for discrimination.

Event Categories

Category	Event Types
Lifecycle	ResponseCreatedEvent, ResponseInProgressEvent, ResponseCompletedEvent, ResponseFailedEvent, ResponseIncompleteEvent, ResponseQueuedEvent, ResponseErrorEvent
Text Output	ResponseTextDeltaEvent, ResponseTextDoneEvent, ResponseRefusalDeltaEvent, ResponseRefusalDoneEvent
Audio Output	ResponseAudioDeltaEvent, ResponseAudioDoneEvent, ResponseAudioTranscriptDeltaEvent, ResponseAudioTranscriptDoneEvent
Reasoning	ResponseReasoningTextDeltaEvent, ResponseReasoningTextDoneEvent, ResponseReasoningSummaryTextDeltaEvent, ResponseReasoningSummaryTextDoneEvent, ResponseReasoningSummaryPartAddedEvent, ResponseReasoningSummaryPartDoneEvent
Content Parts	ResponseContentPartAddedEvent, ResponseContentPartDoneEvent, ResponseOutputItemAddedEvent, ResponseOutputItemDoneEvent
Tool Calls	ResponseFunctionCallArgumentsDeltaEvent, ResponseFunctionCallArgumentsDoneEvent, ResponseWebSearchCall*, ResponseFileSearchCall*, ResponseCodeInterpreterCall*, ResponseImageGenCall*, ResponseMcpCall*, ResponseCustomToolCallInput*
Annotations	ResponseOutputTextAnnotationAddedEvent

Usage Examples

from openai.types.responses import ResponseStreamEvent
import openai

client = openai.OpenAI()

stream = client.responses.create(
    model="gpt-4o",
    input="Hello, world!",
    stream=True,
)

def handle_event(event: ResponseStreamEvent) -> None:
    if event.type == "response.output_text.delta":
        print(event.delta, end="", flush=True)
    elif event.type == "response.completed":
        print("\nResponse complete.")

for event in stream:
    handle_event(event)

Related Pages

• Environment:Openai_Openai_python_Python_3_9_Plus