Implementation:Openai Openai python Response Function Call Args Delta

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 emitted when there is a partial function-call arguments delta, provided by the openai-python SDK.

Description

ResponseFunctionCallArgumentsDeltaEvent is a Pydantic model representing a streaming event emitted when the model produces a partial update (delta) to the arguments of a function call. It contains a delta string with the incremental arguments data, an item_id identifying the output item, an output_index indicating the position of the output item, a sequence_number for event ordering, and a fixed type of "response.function_call_arguments.delta". This type is auto-generated from the OpenAI OpenAPI specification by Stainless.

Usage

Import ResponseFunctionCallArgumentsDeltaEvent when processing streaming events and you need to incrementally assemble function call arguments as they stream in from the model.

Code Reference

Source Location

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

Signature

class ResponseFunctionCallArgumentsDeltaEvent(BaseModel):
    """Emitted when there is a partial function-call arguments delta."""

    delta: str
    item_id: str
    output_index: int
    sequence_number: int
    type: Literal["response.function_call_arguments.delta"]

Import

from openai.types.responses import ResponseFunctionCallArgumentsDeltaEvent

I/O Contract

Fields

Name	Type	Required	Description
delta	str	Yes	The function-call arguments delta that is added.
item_id	str	Yes	The ID of the output item that the delta is added to.
output_index	int	Yes	The index of the output item that the delta is added to.
sequence_number	int	Yes	The sequence number of this event.
type	Literal["response.function_call_arguments.delta"]	Yes	The type of the event. Always "response.function_call_arguments.delta".

Usage Examples

from openai.types.responses import ResponseFunctionCallArgumentsDeltaEvent

# Accumulate function call arguments from streaming deltas
args_buffer = ""
for event in stream:
    if isinstance(event, ResponseFunctionCallArgumentsDeltaEvent):
        args_buffer += event.delta
        print(f"Arguments so far: {args_buffer}")

# Parse the complete arguments JSON
import json
arguments = json.loads(args_buffer)

Related Pages

• Environment:Openai_Openai_python_Python_3_9_Plus