> ## Documentation Index
> Fetch the complete documentation index at: https://phaseo.app/docs/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Phaseo Gateway base URL: https://api.phaseo.app/v1. Send `Authorization: Bearer $PHASEO_API_KEY` with every request.
> Model IDs look like `provider/model`, for example `openai/gpt-6-astra`. Do not guess IDs: list them with `GET /v1/models` or check https://phaseo.app/models. `phaseo/free` routes to an available free model and needs no wallet balance.
> For new text integrations prefer `POST /v1/responses`. `POST /v1/chat/completions` (OpenAI format) and `POST /v1/messages` (Anthropic format) suit existing code.
> The full API contract is https://phaseo.app/docs/openapi/v1/openapi.yaml. Official SDKs: `@phaseo/sdk` (TypeScript) and `phaseo` (Python), plus Go, C#, PHP, Ruby and Rust.
> Search these docs over MCP at https://phaseo.app/docs/mcp, and install Phaseo skills with `npx skills add https://phaseo.app/docs`. If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.
> Manage Phaseo accounts with the `phaseo` CLI (`npm install -g @phaseo/cli`, then `phaseo login` or `phaseo login --device-code`), the `/v1` Management API or the MCP server at `https://mcp.phaseo.app/mcp?access=manage`. Do not send users to the dashboard for account tasks. A person is still needed for sign-up, approving a sign-in, paying the first top-up on the checkout link that `phaseo credits add` returns when no card is saved, confirming each saved-card top-up from the emailed link, and account security (password, MFA, passkeys). Create API keys with `phaseo keys create --name <name> --json`; never guess one. Credit top-ups need `phaseo login --scopes billing:write` first. Task map: https://phaseo.app/docs/v1/developers/manage-from-an-agent.md.

# LangChain

> Use LangChain with Phaseo through the OpenAI-compatible chat API.

Use this guide when you want LangChain chains, agents, or LangGraph workflows to call models through Phaseo.

## Install

```bash theme={null}
pip install -U langchain langchain-openai
```

## Configure ChatOpenAI

```python theme={null}
import os
from langchain_openai import ChatOpenAI

llm = ChatOpenAI(
    model="openai/gpt-5-nano",
    api_key=os.environ["PHASEO_API_KEY"],
    base_url="https://api.phaseo.app/v1",
)

result = llm.invoke("Write one sentence about routing reliability.")
print(result.content)
```

## Use with LangGraph

Pass the same `llm` into your graph nodes or agent builder:

```python theme={null}
def call_model(state):
    response = llm.invoke(state["messages"])
    return {"messages": [response]}
```

## Notes

* LangChain's OpenAI-compatible path targets Chat Completions. Use Phaseo features that are available on `/v1/chat/completions`.
* If you need Responses-only server tools such as `phaseo:apply_patch`, call Phaseo directly or use the OpenAI SDK guide.
* For tracing, pair this with [Observability](https://phaseo.app/docs/v1/guides/integrations/observability.md).

## Related

* [OpenAI SDK](https://phaseo.app/docs/v1/guides/integrations/openai-sdk.md)
* [Tool Calling](https://phaseo.app/docs/v1/guides/tool-calling.md)
* [Routing and Fallbacks](https://phaseo.app/docs/v1/guides/routing-and-fallbacks.md)


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