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The server-client architecture allows you to run GR00T inference on a remote GPU server while controlling robots from a separate client machine. This setup uses ZeroMQ for fast, low-latency communication.

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Architecture overview

The PolicyServer runs on a GPU-equipped machine and handles inference requests, while PolicyClient runs on your robot controller or simulation environment: 
# Server side (GPU machine)
from gr00t.policy.server_client import PolicyServer
from gr00t.policy.gr00t_policy import Gr00tPolicy

policy = Gr00tPolicy(
    embodiment_tag="GR1",
    model_path="nvidia/GR00T-N1.6-3B",
    device="cuda"
)
server = PolicyServer(policy, host="0.0.0.0", port=5555)
server.run()

# Client side (robot controller)
from gr00t.policy.server_client import PolicyClient

policy = PolicyClient(host="192.168.1.100", port=5555)
action, info = policy.get_action(observation)

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Starting the server

1
Launch the policy server
2
Use the provided server script to start inference:
3
uv run python gr00t/eval/run_gr00t_server.py \
    --embodiment-tag GR1 \
    --model-path nvidia/GR00T-N1.6-3B \
    --device cuda:0 \
    --host 0.0.0.0 \
    --port 5555
4
Verify the server is running
5
You should see:
6
Starting GR00T inference server...
  Embodiment tag: GR1
  Model path: nvidia/GR00T-N1.6-3B
  Device: cuda
  Host: 0.0.0.0
  Port: 5555
Server is ready and listening on tcp://0.0.0.0:5555
7
Test connectivity
8
From the client machine:
9
from gr00t.policy.server_client import PolicyClient

policy = PolicyClient(host="192.168.1.100", port=5555)
if policy.ping():
    print("Connected successfully!")
else:
    print("Connection failed")

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Server configuration

The PolicyServer class provides several configuration options:

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Basic configuration

server = PolicyServer(
    policy=policy,
    host="*",           # Bind to all interfaces
    port=5555,          # Default port
    api_token=None      # Optional authentication
)

​
With authentication

server = PolicyServer(
    policy=policy,
    host="0.0.0.0",
    port=5555,
    api_token="your-secret-token"
)
On the client side: 
policy = PolicyClient(
    host="192.168.1.100",
    port=5555,
    api_token="your-secret-token"
)

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Server endpoints

The server registers these endpoints by default:
  • ping: Health check endpoint
  • kill: Gracefully shutdown the server
  • get_action: Get action from observation
  • reset: Reset policy state
  • get_modality_config: Retrieve modality configuration

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Client usage

The PolicyClient implements the same interface as BasePolicy: 
from gr00t.policy.server_client import PolicyClient

# Initialize client
policy = PolicyClient(
    host="localhost",
    port=5555,
    timeout_ms=15000,  # Request timeout
    strict=False        # Disable client-side validation
)

# Get modality configuration
modality_config = policy.get_modality_config()

# Reset policy
policy.reset(options={"episode_index": 0})

# Get action
action, info = policy.get_action(observation)

# Shutdown server (optional)
policy.kill_server()

​
Timeout configuration

Configure request timeout based on your inference latency: 
policy = PolicyClient(
    host="192.168.1.100",
    port=5555,
    timeout_ms=30000  # 30 second timeout for slow networks
)

​
Custom endpoints

Register custom endpoints for application-specific functionality: 
from gr00t.policy.server_client import PolicyServer

def custom_handler(param1: str, param2: int) -> dict:
    # Your custom logic
    return {"result": f"Processed {param1} with {param2}"}

server = PolicyServer(policy, port=5555)
server.register_endpoint(
    "custom_endpoint",
    custom_handler,
    requires_input=True
)
server.run()
Call from client: 
result = policy.call_endpoint(
    "custom_endpoint",
    data={"param1": "test", "param2": 42}
)

​
Message serialization

The server uses MessagePack for efficient serialization with custom handling for NumPy arrays and modality configs: 
class MsgSerializer:
    @staticmethod
    def encode_custom_classes(obj):
        if isinstance(obj, np.ndarray):
            output = io.BytesIO()
            np.save(output, obj, allow_pickle=False)
            return {"__ndarray_class__": True, "as_npy": output.getvalue()}
        # ... other types
This ensures fast, zero-copy transfer of large arrays like images.

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Debugging with replay policy

Test your client integration without a trained model: 
uv run python gr00t/eval/run_gr00t_server.py \
    --dataset-path demo_data/gr1.PickNPlace \
    --embodiment-tag GR1 \
    --execution-horizon 8
The server replays actions from the dataset. Switch episodes with: 
policy.reset(options={"episode_index": 5})
The replay policy is useful for verifying environment setup, observation formatting, and action execution without requiring a trained model.

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Network considerations

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Firewall configuration

Ensure port 5555 (or your chosen port) is open: 
# On server machine
sudo ufw allow 5555/tcp

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Latency optimization

For low-latency applications:
  1. Use dedicated network interfaces
  2. Disable TCP Nagle’s algorithm (ZeroMQ does this by default)
  3. Run server and client on the same machine when possible
  4. Consider using InfiniBand or high-speed Ethernet
The server binds to 0.0.0.0 by default, making it accessible from any network interface. Use api_token authentication or firewall rules to restrict access in production deployments.

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Error handling

The server catches exceptions and returns error responses: 
try:
    action, info = policy.get_action(observation)
except RuntimeError as e:
    if "Server error" in str(e):
        print(f"Server error: {e}")
        # Reconnect or handle error
Common errors:
  • "Unauthorized: Invalid API token": Authentication failed
  • "Unknown endpoint": Endpoint not registered
  • Connection timeout: Server unreachable or overloaded

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Server script configuration

The run_gr00t_server.py script supports additional options: 
@dataclass
class ServerConfig:
    model_path: str | None = None
    embodiment_tag: EmbodimentTag = EmbodimentTag.NEW_EMBODIMENT
    device: str = "cuda"
    dataset_path: str | None = None  # For replay policy
    modality_config_path: str | None = None
    execution_horizon: int | None = None
    host: str = "0.0.0.0"
    port: int = 5555
    strict: bool = True
    use_sim_policy_wrapper: bool = False
Example with simulation wrapper: 
uv run python gr00t/eval/run_gr00t_server.py \
    --model-path nvidia/GR00T-N1.6-3B \
    --embodiment-tag GR1 \
    --use-sim-policy-wrapper

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