codex-backend-sdk 0.3.0

Unofficial Python SDK for the ChatGPT Codex backend API

codex-backend-sdk

Unofficial Python SDK for the ChatGPT Codex backend API (chatgpt.com/backend-api/codex).

This package mirrors the official OpenAI Python SDK shape for the API surface that the Codex backend exposes. Use OpenAI, client.responses.create(...), and client.models.list() just as you would with openai-python, with Codex-specific authentication and backend limitations under the hood.

Requirements: a ChatGPT Plus, Pro, or Enterprise subscription. Authentication goes through ChatGPT OAuth and stores tokens in ~/.codex/auth.json.

Disclaimer: This is an independent, community-maintained library that reverse-engineers undocumented endpoints of chatgpt.com. It is not affiliated with, endorsed by, or supported by OpenAI.

Installation

git clone https://github.com/B4PT0R/codex-backend-sdk.git
cd codex-backend-sdk
pip install -e .

Basic Usage

from codex_backend_sdk import OpenAI

client = OpenAI().authenticate()

response = client.responses.create(
    model="gpt-5.4",
    input="Explain quicksort in one paragraph.",
)

print(response.output_text)

Streaming

stream = client.responses.create(
    model="gpt-5.4",
    input="Say 'hi' five times.",
    stream=True,
)

for event in stream:
    if event.type in {"response.output_text.delta", "response.content_part.delta"}:
        delta = event.delta
        print(delta if isinstance(delta, str) else delta.get("text", ""), end="")

Models

models = client.models.list()
for model in models:
    print(model.id, model.display_name, model.context_window)

info = client.models.retrieve("gpt-5.4")

Multi-Turn Input

The Codex backend does not expose previous_response_id, so pass prior input/output items explicitly.

history = [
    {"role": "user", "content": "My name is Alice. Say OK."},
]

reply1 = client.responses.create(input=history).output_text
history.append({"role": "assistant", "content": reply1})
history.append({"role": "user", "content": "What is my name?"})

reply2 = client.responses.create(input=history).output_text
print(reply2)

Function Calling

import json

tools = [{
    "type": "function",
    "name": "get_weather",
    "description": "Get the current weather for a city.",
    "parameters": {
        "type": "object",
        "properties": {"city": {"type": "string"}},
        "required": ["city"],
        "additionalProperties": False,
    },
}]

first = client.responses.create(
    input="What's the weather in Paris?",
    tools=tools,
)

call = next(item for item in first.output if item["type"] == "function_call")
result = {"temperature": 18, "unit": "celsius", "condition": "cloudy"}

second = client.responses.create(
    input=[
        call,
        {
            "type": "function_call_output",
            "call_id": call["call_id"],
            "output": json.dumps(result),
        },
    ],
    tools=tools,
)

print(second.output_text)

Structured Output

schema = {
    "title": "person",
    "type": "object",
    "properties": {
        "name": {"type": "string"},
        "age": {"type": "integer"},
    },
    "required": ["name", "age"],
    "additionalProperties": False,
}

response = client.responses.create(
    input="Extract: Bob is 42 years old.",
    text={
        "format": {
            "type": "json_schema",
            "name": "person",
            "schema": schema,
            "strict": True,
        }
    },
)

Supported Backend Endpoints

The SDK exposes the supported backend endpoints through either OpenAI-shaped resources (responses, models, realtime) or Codex-only resources (codex).

Backend endpoint	SDK method	Notes
POST /backend-api/codex/responses	client.responses.create(...)	Stream-only backend; non-streaming SDK calls are collected from SSE events.
POST /backend-api/codex/responses/compact	client.responses.compact(...)	Codex-specific helper for encrypted context compaction.
GET /backend-api/codex/models	client.models.list() / client.models.retrieve(...)	OpenAI-shaped model objects with Codex metadata preserved as extra fields.
POST /backend-api/codex/realtime/calls	client.realtime.calls.create(...)	OpenAI-shaped SDP call creation for realtime sessions.
wss://api.openai.com/v1/realtime?model=...	client.realtime_websocket_url(...) / client.realtime_websocket_headers(...)	Helper surface used by codex-agent's realtime plugin.
POST /v1/embeddings	client.embeddings.create(...)	Uses the Codex OAuth access token against api.openai.com; verified with text-embedding-3-small.
POST /v1/audio/transcriptions	client.audio.transcriptions.create(...)	Uses the Codex OAuth access token against api.openai.com; verified with gpt-4o-mini-transcribe.
GET /backend-api/wham/usage	client.codex.usage()	Codex/ChatGPT quota and rate-limit status.
GET /backend-api/wham/tasks/list	client.codex.tasks.list(...)	Raw Codex cloud task listing.
GET /backend-api/wham/tasks/{task_id}	client.codex.tasks.retrieve(task_id)	Raw Codex cloud task detail.
GET /backend-api/wham/tasks/{task_id}/turns	client.codex.tasks.turns.list(task_id)	Raw task turn mapping.
GET /backend-api/wham/tasks/{task_id}/turns/{turn_id}/sibling_turns	client.codex.tasks.turns.sibling_turns(task_id, turn_id)	Raw sibling turn list.
GET /backend-api/wham/environments	client.codex.environments.list()	Raw Codex cloud environment list.
GET /backend-api/memories	client.codex.memories.list()	Raw ChatGPT memory payload for the authenticated account.
GET /backend-api/user_system_messages	client.codex.user_system_messages.retrieve()	Raw ChatGPT customization/system-message payload.

Responses

client.responses.create(...) follows the official OpenAI Responses API where the Codex backend overlaps with it.

Supported request fields:

• model
• input
• instructions
• include
• parallel_tool_calls
• prompt_cache_key
• reasoning
• service_tier
• store=False
• stream
• text
• tool_choice
• tools

The backend itself requires streaming. When stream=True, the SDK yields ResponseStreamEvent objects directly. When stream is omitted or false, the SDK consumes the SSE stream and returns a collected Response.

response = client.responses.create(
    model="gpt-5.4",
    instructions="Be concise.",
    input=[
        {"role": "user", "content": "Summarize this API shape."},
    ],
    reasoning={"effort": "medium", "summary": "auto"},
    include=["reasoning.encrypted_content"],
    text={"verbosity": "medium"},
    prompt_cache_key="session-123",
)

Unsupported official Responses parameters are rejected explicitly with CodexBackendUnsupportedParameterError, including temperature, top_p, max_output_tokens, metadata, user, safety_identifier, truncation, previous_response_id, conversation, background, prompt, prompt_cache_retention, and stream_options.

Context Compaction

client.responses.compact(...) is specific to the Codex backend. It compresses a long Responses-style input list into an opaque encrypted compaction summary that can be replayed in later input arrays.

compacted = client.responses.compact(
    model="gpt-5.4",
    instructions="Keep task-critical context.",
    input=history,
)

history = compacted.output

The returned CompactedResponse.output contains regular response items plus one or more {"type": "compaction_summary", ...} items. Treat those summaries as opaque backend state.

Models

client.models.list() and client.models.retrieve(model) mirror the official OpenAI models resource, while preserving Codex-specific metadata as extra Pydantic fields.

models = client.models.list()
for model in models:
    print(
        model.id,
        model.context_window,
        model.supported_in_api,
        model.supports_reasoning_summaries,
    )

Common extra fields include:

• display_name
• description
• context_window
• supported_in_api
• supports_reasoning_summaries
• support_verbosity
• default_verbosity
• default_reasoning_level
• supported_reasoning_levels
• auto_compact_token_limit
• prefer_websockets
• input_modalities
• available_in_plans
• base_instructions
• priority
• raw

Realtime

The SDK keeps the realtime surface available for integrations that bridge Codex auth with voice sessions.

client.realtime.calls.create(...) mirrors the official OpenAI SDK call shape:

answer = client.realtime.calls.create(
    sdp=offer_sdp,
    session={"type": "realtime", "model": "gpt-realtime-1.5"},
)

print(answer.text)

For WebSocket-based plugins such as codex-agent, the client also exposes small helpers that reuse the OpenAI API key stored by the Codex OAuth flow:

url = client.realtime_websocket_url(model="gpt-realtime-1.5")
headers = client.realtime_websocket_headers(session_id="voice-session")

realtime_websocket_headers(...) requires ~/.codex/auth.json to contain openai_api_key. The default authenticate(request_api_key=True) flow stores that key when available.

Embeddings

client.embeddings.create(...) mirrors the official OpenAI embeddings resource and sends the Codex OAuth access token directly to api.openai.com/v1.

embedding = client.embeddings.create(
    model="text-embedding-3-small",
    input="Embed this sentence.",
    dimensions=256,
)

print(embedding.data[0].embedding)

Audio Transcriptions

client.audio.transcriptions.create(...) mirrors the official OpenAI transcriptions resource for non-streaming calls.

with open("meeting.wav", "rb") as audio:
    transcription = client.audio.transcriptions.create(
        model="gpt-4o-mini-transcribe",
        file=("meeting.wav", audio, "audio/wav"),
        response_format="json",
    )

print(transcription.text)

Quota And Usage

client.codex.usage() calls the ChatGPT WHAM usage endpoint. It returns the raw quota payload from the backend because the shape contains plan-specific fields.

quota = client.codex.usage()
primary = quota.get("rate_limit", {}).get("primary_window", {})
print(primary.get("used_percent"))

Typical fields include:

• plan_type
• rate_limit.allowed
• rate_limit.limit_reached
• rate_limit.primary_window
• rate_limit.secondary_window
• additional_rate_limits
• credits
• rate_limit_reached_type

Codex Cloud Tasks

The client.codex.tasks and client.codex.environments namespaces expose read-only WHAM cloud-task payloads as raw backend dictionaries.

tasks = client.codex.tasks.list(limit=10)
task = client.codex.tasks.retrieve(tasks["items"][0]["id"])
turns = client.codex.tasks.turns.list(task["task"]["id"])
environments = client.codex.environments.list()

Supported task-list filters are limit, cursor, task_filter, and environment_id.

ChatGPT Account Data

The client.codex namespace also exposes read-only ChatGPT account data that is not part of the official OpenAI SDK.

memories = client.codex.memories.list()
customization = client.codex.user_system_messages.retrieve()

Both methods return raw backend dictionaries because these payloads can contain personal account-specific fields and may change without notice.

Observed But Not Exposed

The reverse-engineering notes in docs/backend-api.md include additional observed endpoints. They are not exposed as SDK resources yet because they are plan-gated, unavailable on chatgpt.com, or not stable enough:

• POST /backend-api/codex/memories/trace_summarize
• GET /backend-api/wham/config/requirements
• POST /v1/audio/speech (auth reaches the endpoint, but Pro OAuth lacks api.model.audio.request in current tests)