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AgentConfig mirrors LangChain’s RunnableConfig fields - pass callbacks, tags, metadata, run_name directly. The entire agent run is wrapped in a single parent trace with all child operations nested automatically. 
from langfuse.langchain import CallbackHandler
from langchain_adk import AgentConfig

run_config = AgentConfig(
    callbacks=[CallbackHandler()],  # Langfuse, LangSmith, or any BaseCallbackHandler
    tags=["production", "user-facing"],
    metadata={"user_id": "u-123"},
    run_name="MyAgent",
)

async for event in runner.astream(
    user_id="user-1",
    session_id="session-1",
    new_message="Hello!",
    config=run_config,
):
    ...
Environment variables - Set the following for Langfuse:
export LANGFUSE_SECRET_KEY="sk-lf-..."
export LANGFUSE_PUBLIC_KEY="pk-lf-..."
export LANGFUSE_BASE_URL="https://cloud.langfuse.com"

​
What gets traced

  • Each agent run as a single parent trace (named after the agent)
  • All LLM calls (ainvoke / astream) as child spans with token usage
  • All tool executions as child spans with inputs/outputs
  • Structured output fallback calls
  • Works with composite agents - each sub-agent creates its own nested trace
A2A boundaries - A2A is HTTP, so callbacks can’t cross the wire. Each A2A server should create its own handler. Link traces by passing a trace_id in task metadata.