How to call the OpenAI Responses API

This page shows how to:

Use a unified API. TensorZero provides the same chat completion format for the Responses API.
Access built-in tools. Enable built-in tools from OpenAI like web_search.
Enable reasoning models. Support models with extended thinking capabilities.

We provide complete code examples on GitHub.

Call the OpenAI Responses API

Python (TensorZero SDK)
Python (OpenAI SDK)
Node (OpenAI SDK)
HTTP

The TensorZero Python SDK provides a unified API for calling OpenAI’s Responses API.

Set up your OpenAI API key

You can set the OPENAI_API_KEY environment variable with your API key.

export OPENAI_API_KEY="sk-..."

Install the TensorZero Python SDK

You can install the TensorZero SDK with a Python package manager like pip.

pip install tensorzero

Configure a model for the OpenAI Responses API

Create a configuration file with a model using api_type = "responses" and provider tools:

tensorzero.toml

[models.gpt-5-mini-responses-web-search]
routing = ["openai"]

[models.gpt-5-mini-responses-web-search.providers.openai]
type = "openai"
model_name = "gpt-5-mini"
api_type = "responses"
include_encrypted_reasoning = true
provider_tools = [{type = "web_search"}]  # built-in OpenAI web search tool
# Enable plain-text summaries of encrypted reasoning
extra_body = [
    { pointer = "/reasoning", value = { effort = "low", summary = "auto" } }
]

If you don’t need to customize the model configuration (e.g. include_encrypted_reasoning, provider_tools), you can use the short-hand model name openai::responses::gpt-5-codex to call it directly.

Deploy a standalone (HTTP) TensorZero Gateway

Let’s deploy a standalone TensorZero Gateway using Docker. For simplicity, we’ll use the gateway with the configuration above.

docker run \
  -e OPENAI_API_KEY \
  -v $(pwd)/tensorzero.toml:/app/config/tensorzero.toml:ro \
  -p 3000:3000 \
  tensorzero/gateway \
  --config-file /app/config/tensorzero.toml

See the TensorZero Gateway Deployment page for more details.

Initialize the TensorZero Gateway client

Let’s initialize the TensorZero Gateway client and point it to the gateway we just launched.

from tensorzero import TensorZeroGateway

t0 = TensorZeroGateway.build_http(gateway_url="http://localhost:3000")

The TensorZero Python SDK includes a synchronous TensorZeroGateway client and an asynchronous AsyncTensorZeroGateway client. Both options support running the gateway embedded in your application with build_embedded or connecting to a standalone gateway with build_http. See Clients for more details.

Call the LLM

OpenAI web search can take up to a minute to complete.

response = t0.inference(
    model_name="gpt-5-mini-responses-web-search",
    input={
        "messages": [
            {
                "role": "user",
                "content": "What is the current population of Japan?",
            }
        ]
    },
    # Thought summaries are enabled in tensorzero.toml via extra_body
)

Sample Response

ChatInferenceResponse(
    inference_id=UUID('0199ff78-6246-7c12-b4b0-6e3a881cc6b9'),
    episode_id=UUID('0199ff78-6246-7c12-b4b0-6e4367f949b8'),
    variant_name='gpt-5-mini-responses-web-search',
    content=[
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo9...',
            summary=[
                ThoughtSummaryBlock(
                    text="I need to search for Japan's current population data.",
                    type='summary_text'
                )
            ],
            _internal_provider_type='openai'
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fda57d481969c3603df0d675348',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': 'Japan population 2025 October 2025 population estimate Statistics Bureau of Japan'
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fdf9b988196b36756d639e2b015',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': "Ministry of Internal Affairs and Communications Japan population Oct 1 2024 'total population' 'Japan' 'population estimates' '2024' 'Oct. 1' '総人口' '令和6年' "
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fe1a388819684971acfdaf4cd44',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': "Ministry of Internal Affairs and Communications population Japan Oct 1 2024 total population 'Oct. 1, 2024' 'population' 'Japan' 'MIC' 'population estimates' '2024' '総人口' "
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fe439788196911a195c70cc8ca9',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {'type': 'search'}
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fe6b140819690a4468d3304fece',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {'type': 'search'}
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59fe81e408196921b69174f6abaf7',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {'type': 'search'}
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59feda6188196827a0b5aa01e96a1',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': "United Nations World Population Prospects 2024 Japan 2025 population 'Japan population 2025' 'World Population Prospects 2024' 'Japan' "
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59ff3cc8881968d1c5c9c1bbe4ecc',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': "UN World Population Prospects 2024 Japan population 2025 '123,103,479' 'Japan 2025' 'World Population Prospects' 'Japan' '2025' "
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        UnknownContentBlock(
            data={
                'id': 'ws_05489a0b57dc84980168f59ff67ed48196a0054a38e96f8e0c',
                'type': 'web_search_call',
                'status': 'completed',
                'action': {
                    'type': 'search',
                    'query': "United Nations population Japan 2025 'World Population Prospects 2024' 'Japan population 2025' site:un.org"
                }
            },
            model_provider_name='tensorzero::model_name::gpt-5-mini-responses-web-search::provider_name::openai',
            type='unknown'
        ),
        Thought(
            text=None,
            type='thought',
            signature='gAAAAABo...',
            _internal_provider_type=None
        ),
        Text(
            text="Short answer: about 123–124 million people.\n\nMore precisely:\n- Japan's official estimate (Ministry of Internal Affairs and Communications / e‑Stat) reported a total population of 123,802,000 (including foreign residents) as of October 1, 2024 (release published Apr 14, 2025). ([e-stat.go.jp](https://www.e-stat.go.jp/en/stat-search/files?layout=dataset&page=1&query=Population+Estimates%2C+natural))  \n- The United Nations (WPP 2024, used by sources such as Worldometer) gives a mid‑2025 estimate of about 123.1 million. ([srv1.worldometers.info](https://srv1.worldometers.info/world-population/japan-population/?utm_source=openai))\n\nDo you want a live "right now" estimate for today (Oct 20, 2025) or a breakdown by Japanese nationals vs. foreign residents? I can fetch the latest live or official figures for the exact date you want.",
            arguments=None,
            type='text'
        )
    ],
    usage=Usage(input_tokens=29904, output_tokens=1921),
    finish_reason=None,
    original_response=None
)

Introduction

Gateway

Optimization

Evaluations

Experimentation

Deployment

Operations

How to call the OpenAI Responses API

Call the OpenAI Responses API

Introduction

Gateway

Optimization

Evaluations

Experimentation

Deployment

Operations

​Call the OpenAI Responses API

Call the OpenAI Responses API