Implementation:Openai Openai python Response Image Gen Call Partial

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

Overview

Concrete streaming event type for delivering partial image data during image generation provided by the openai-python SDK.

Description

ResponseImageGenCallPartialImageEvent is a Pydantic model emitted when a partial image is available during image generation streaming. It carries the item_id identifying the image generation item, the output_index locating it in the response output array, partial_image_b64 containing the base64-encoded partial image data suitable for rendering, partial_image_index as a 0-based index for the partial image chunk, and a sequence_number for event ordering. The type field is always "response.image_generation_call.partial_image".

Usage

Import this type when building streaming event handlers that render progressive image previews as partial image data arrives from the server.

Code Reference

Source Location

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

Signature

class ResponseImageGenCallPartialImageEvent(BaseModel):
    """Emitted when a partial image is available during image generation streaming."""

    item_id: str
    output_index: int
    partial_image_b64: str
    partial_image_index: int
    sequence_number: int
    type: Literal["response.image_generation_call.partial_image"]

Import

from openai.types.responses import ResponseImageGenCallPartialImageEvent

I/O Contract

Fields

Name	Type	Required	Description
item_id	str	Yes	The unique identifier of the image generation item being processed.
output_index	int	Yes	The index of the output item in the response's output array.
partial_image_b64	str	Yes	Base64-encoded partial image data, suitable for rendering as an image.
partial_image_index	int	Yes	0-based index for the partial image (backend is 1-based, but this is 0-based for the user).
sequence_number	int	Yes	The sequence number of the image generation item being processed.
type	Literal["response.image_generation_call.partial_image"]	Yes	The type of the event. Always response.image_generation_call.partial_image.

Usage Examples

import base64
import openai

client = openai.OpenAI()

stream = client.responses.create(
    model="gpt-4o",
    input="Generate an image of a sunset over mountains.",
    stream=True,
)

for event in stream:
    if event.type == "response.image_generation_call.partial_image":
        # Decode and display partial image preview
        partial_bytes = base64.b64decode(event.partial_image_b64)
        print(f"Received partial image chunk {event.partial_image_index} "
              f"({len(partial_bytes)} bytes)")

Related Pages

• Environment:Openai_Openai_python_Python_3_9_Plus