> ## 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 If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.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.

# Responses API

> Generate text and tool calls through the Phaseo Responses API from Rust.

Use `responses(...)` for new text-generation and tool-calling work.

```rust theme={null}
use phaseo::Phaseo;
use serde_json::json;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Phaseo::from_env()?;
    let response = client.responses(&json!({
        "model": "openai/gpt-6-astra",
        "input": "Give three concise benefits of model routing.",
        "max_output_tokens": 200
    }))?;

    println!("status: {}", response.status);
    println!("request ID: {:?}", response.request_id);
    println!("{}", serde_json::to_string_pretty(&response.body)?);
    Ok(())
}
```

## Read the output text

Responses API output is an array. For a simple text result:

```rust theme={null}
use serde_json::Value;

let text = response.body
    .get("output")
    .and_then(Value::as_array)
    .into_iter()
    .flatten()
    .filter(|item| item.get("type").and_then(Value::as_str) == Some("message"))
    .flat_map(|item| {
        item.get("content")
            .and_then(Value::as_array)
            .into_iter()
            .flatten()
    })
    .find_map(|part| {
        (part.get("type").and_then(Value::as_str) == Some("output_text"))
            .then(|| part.get("text").and_then(Value::as_str))
            .flatten()
    });
```

Keep the full `body` when your request can return multiple messages, reasoning items, tool calls, or provider metadata.

## Send function tools

```rust theme={null}
let response = client.responses(&json!({
    "model": "openai/gpt-6-astra",
    "input": "Check the weather in London.",
    "tools": [{
        "type": "function",
        "name": "get_weather",
        "description": "Get the current weather for a city.",
        "parameters": {
            "type": "object",
            "properties": {
                "city": { "type": "string" }
            },
            "required": ["city"]
        }
    }]
}))?;
```

For a local tool loop with approvals and resumable state, use the [Rust Agent SDK](https://phaseo.app/docs/v1/sdk-reference/rust/agent-sdk-overview.md).

## Related

* [Responses API reference](https://phaseo.app/docs/v1/api-reference/endpoint/responses.md)
* [Build with the Rust Agent SDK](https://phaseo.app/docs/v1/sdk-reference/rust/agent-sdk.md)


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.