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Signature

def instrument_baml(baml_client: Any) -> Any

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Overview

Unlike Anthropic, OpenAI, LangChain, and Gemini — which are auto-instrumented automatically — BAML clients are code-generated per project and cannot be monkey-patched. You must explicitly wrap the client with instrument_baml().
If you use BAML without calling instrument_baml(), calls will not be traced. There is no error — they simply won’t appear in traces.

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Parameters

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baml_client
Any
required
The BAML client instance to wrap. Typically imported as b from baml_client.

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Returns

A proxy-wrapped client with tracing enabled. Assign the result back to your client variable.

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Example

from baml_client import b
from rdk import observe, instrument_baml

# Required: wrap the BAML client before use
b = instrument_baml(b)

@observe(name="extract-entities")
async def process(text: str):
    return await b.ExtractEntities(text)  # Auto-traced!

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How It Works

instrument_baml() wraps the BAML client in a proxy that intercepts method calls. When a BAML function is called:
  1. The proxy detects the active trace (from @observe or trace())
  2. A span is created with the function name and arguments
  3. The real BAML function executes normally
  4. The span is completed with the structured result and token usage

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What Gets Captured

FieldDescription
typeLLM
nameBAML function name (e.g., baml.ClassifyInquiry)
input.argsFunction arguments
output.resultStructured result
token_usageToken counts
metadata.provider"baml"

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See Also