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 If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.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

# Chat Completions

> Send OpenAI-compatible Chat Completions requests with the Rust SDK.

Use `chat_completions(...)` when an existing integration already uses message-based Chat Completions payloads.

```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.chat_completions(&json!({
        "model": "openai/gpt-6-astra",
        "messages": [
            {
                "role": "system",
                "content": "Answer concisely."
            },
            {
                "role": "user",
                "content": "What is provider fallback?"
            }
        ]
    }))?;

    let text = response
        .body
        .pointer("/choices/0/message/content")
        .and_then(|value| value.as_str())
        .unwrap_or("");

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

For new integrations, prefer the [Responses API](https://phaseo.app/docs/v1/sdk-reference/rust/responses.md). It provides one request model for text, multimodal input, tools, and richer output items.

## Related

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


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