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 If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.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

# Usage

> Create a Rust client, send Gateway requests, and handle responses and errors.

Use `Phaseo` when your Rust service needs a synchronous Phaseo Gateway client.

## Create a client

Load the API key and optional base URL from the environment:

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

let client = Phaseo::from_env()?;
```

Or pass the key directly:

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

let client = Phaseo::new("phaseo_v1_sk_...")?;
```

`Phaseo` redacts the API key and custom header values from its `Debug` output.

## Send a Responses request

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

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Phaseo::from_env()?;
    let response = client.responses(&json!({
        "model": "openai/gpt-6-astra",
        "input": "Summarize why provider fallbacks improve reliability."
    }))?;

    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()
        })
        .unwrap_or("");

    println!("{text}");
    Ok(())
}
```

The complete JSON response remains available in `response.body`.

## Send a Chat Completions request

```rust theme={null}
let response = client.chat_completions(&json!({
    "model": "openai/gpt-6-astra",
    "messages": [{
        "role": "user",
        "content": "Reply with exactly: chat works"
    }]
}))?;

println!("{}", response.body);
```

## Call another JSON endpoint

Use `post(...)` for a Phaseo endpoint that does not yet have a high-level helper:

```rust theme={null}
let response = client.post("/embeddings", &json!({
    "model": "openai/text-embedding-3-small",
    "input": "Phaseo routes across AI providers"
}))?;
```

The path may include or omit its leading slash.

## Add a request header

```rust theme={null}
let client = Phaseo::from_env()?
    .with_header("x-phaseo-workspace-id", "workspace_123");
```

## Handle Gateway errors

```rust theme={null}
let request = serde_json::json!({
    "model": "openai/gpt-6-astra",
    "input": "Handle this request"
});

match client.responses(&request) {
    Ok(response) => println!("{}", response.body),
    Err(error) => {
        eprintln!("message: {}", error.message);
        eprintln!("status: {:?}", error.status);
        eprintln!("body: {:?}", error.body);
    }
}
```

`PhaseoError` contains an HTTP status and parsed JSON body when the Gateway returned an error. Transport and configuration failures have no HTTP status.

## Next

* [Responses API](https://phaseo.app/docs/v1/sdk-reference/rust/responses.md)
* [Chat Completions](https://phaseo.app/docs/v1/sdk-reference/rust/chat-completions.md)
* [Rust API reference](https://phaseo.app/docs/v1/sdk-reference/rust/api-reference.md)


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