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simplify langchain distributed tracing example #2436

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447e9cd
Refactor trace ID handling in Langchain execution
klaasmeinke Jan 7, 2026
9dd17bd
Update pages/docs/observability/features/trace-ids-and-distributed-tr…
klaasmeinke Jan 9, 2026
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28 changes: 7 additions & 21 deletions pages/docs/observability/features/trace-ids-and-distributed-tracing.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -293,7 +293,7 @@ const completion = await openai.chat.completions.create({
</Tab>
<Tab>

To pass a custom trace ID to a Langchain execution, you can wrap the execution in a span that sets a predefined trace ID. You can also retrieve the last trace ID a callback handler has created via `langfuse_handler.last_trace_id`.
To pass a custom trace ID to a Langchain execution, you can add a trace ID to the callback handler using the `trace_context` argument. You can also retrieve the last trace ID a callback handler has created via `langfuse_handler.last_trace_id`.

```python
from langfuse import get_client, Langfuse
Expand All @@ -305,27 +305,13 @@ langfuse = get_client()
external_request_id = "req_12345"
predefined_trace_id = Langfuse.create_trace_id(seed=external_request_id)

langfuse_handler = CallbackHandler()
langfuse_handler = CallbackHandler(trace_context={"trace_id": predefined_trace_id})

# Use the predefined trace ID with trace_context
with langfuse.start_as_current_observation(
as_type="span",
name="langchain-request",
trace_context={"trace_id": predefined_trace_id}
) as span:

with propagate_attributes(
span.update_trace(
input={"person": "Ada Lovelace"}
)

# LangChain execution will be part of this trace
response = chain.invoke(
{"person": "Ada Lovelace"},
config={"callbacks": [langfuse_handler]}
)

span.update_trace(output={"response": response})
# LangChain execution will be part of this trace
response = chain.invoke(
{"person": "Ada Lovelace"},
config={"callbacks": [langfuse_handler]}
)

print(f"Trace ID: {predefined_trace_id}") # Use this for scoring later
print(f"Trace ID: {langfuse_handler.last_trace_id}") # Care needed in concurrent environments where handler is reused
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