# 01 Hello Agent

Script: `example/01_hello_agent.py`.

This is the smallest OpenRath program: build a `flow.Agent`, pass it a `Session`, and receive an updated session.

```bash
python example/01_hello_agent.py
```

| Concept | API |
| --- | --- |
| Agent as module | `flow.Agent(system_prompt, provider, on_event=...)` |
| Session as runtime value | `Session.from_user_message(...).to("local")` |
| Streaming callback | `on_event=stream_to_stdout()` |
| Usage accounting | `out.cumulative_usage` |

Needs an OpenAI-compatible key or `llm.default_provider` config.

[← Runnable Examples](index.md)