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

# Inference

> Send observations in OpenPI's format and get action chunks back.

`relay.Policy` connects to a policy server and works like OpenPI's `WebsocketClientPolicy`: you send an observation dict and get a dict back with the actions in it.

```python theme={null}
import relay

policy = relay.Policy("wss://<your policy server>")

example = {
    "image": {
        "base_0_rgb": front,          # (H, W, 3) uint8 RGB, or JPEG bytes
        "left_wrist_0_rgb": wrist,
    },
    "state": joints,                  # (32,) float32
    "prompt": "pick up the fork",
}
action_chunk = policy.infer(example)["actions"]   # (action_horizon, 32) float32
```

Use one `Policy` for the whole run, and close it when you're done, or use it in a `with` block:

```python theme={null}
with relay.Policy("wss://<your policy server>") as policy:
    while running:
        actions = policy.infer(get_observation())["actions"]
```

## The observation

**image** `dict[str, image]` *required*

One frame per camera, by the model's camera names: for π0.5, `base_0_rgb`, `left_wrist_0_rgb` and `right_wrist_0_rgb`. A frame is an `(H, W, 3)` `uint8` RGB array, of any size: the server resizes it to 224×224, keeping its aspect ratio and padding the short side. Cameras you leave out are masked out.

**state** `float array` *required*

The robot's state, `(32,)` for π0.5, as the model was trained on it (normalized, padded with zeros).

**prompt** `str` *required*

The task in plain language. The server tokenizes it as the model was trained. Code that sends OpenPI's `tokenized_prompt` and `tokenized_prompt_mask` instead still works.

**image\_mask** `dict[str, bool]`

Which cameras are present. By default, the ones in `image`.

**num\_steps** `int`

Denoising steps for this request. Fewer are faster and slightly less precise. By default, the server's (`get_server_metadata()["num_steps"]`).

**adapter\_dir** `str`

A LoRA adapter the server holds, for this request. By default, the server's.

## The reply

**actions** `np.ndarray`

`(action_horizon, action_dim)` `float32`: the next actions, in the model's units (as its training data was normalized). `actions[0]` is the one to take now.

**policy\_timing** `dict`

`infer_ms`: time in the server's engine, queued and run.

**server\_timing** `dict`

`infer_ms`, `parse_ms` (unpacking and decoding the request) and, from the second request on, `prev_total_ms` (the last round trip as the server saw it).

## What the policy takes

`get_server_metadata()` returns what the server sent when you connected:

```python theme={null}
policy.get_server_metadata()
# {"model": "pi05", "cameras": ["base_0_rgb", "left_wrist_0_rgb", "right_wrist_0_rgb"],
#  "state_dim": 32, "action_horizon": 50, "action_dim": 32, "num_steps": 10}
```

## Sending images

Frames are compressed before they're sent. Pick the codec when you connect:

```python theme={null}
policy = relay.Policy(url, codec=relay.Codec.LOSSLESS)
```

| Codec | Size of a 224×224 frame | Quality |
| - | - | - |
| `Codec.LOSSLESS` | 45.9 KB | exact pixels |
| `Codec.JPEG_Q100` | 38.0 KB | 54.6 dB PSNR |
| `Codec.JPEG_Q98` | 23.1 KB | 48.8 dB |
| `Codec.JPEG_Q95` | 15.1 KB | 45.4 dB |
| `Codec.JPEG_Q92` | 11.5 KB | 43.7 dB |
| `Codec.JPEG_Q90` (default) | 10.4 KB | 42.9 dB |
| `Codec.JPEG_Q85` | 7.0 KB | 40.3 dB |
| `Codec.JPEG_Q50` | 3.8 KB | 36.7 dB |

JPEG frames are smaller, so they upload faster on a slow connection; the server decodes them on its GPU. If your camera already gives you JPEG bytes, put them in `image` as they are, with a JPEG codec.

## Errors

If the server fails a request (a wrong state length, say), `infer` raises `RuntimeError` with the server's traceback, and the server closes the connection. Connect again to go on. A call on a closed connection raises `websockets.exceptions.ConnectionClosed`.

## Options

`relay.Policy(url, codec=Codec.JPEG_Q90, headers=None)`

**url** `str` *required*

The policy server's websocket URL, `wss://...`.

**codec** `relay.Codec` (default: Codec.JPEG\_Q90)

How frames are sent.

**headers** `dict[str, str]`

Extra headers for the connection, such as a proxy's credentials.

Connecting waits as long as the server takes to start, which can be minutes on a cold one.


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