hi @liurui-1

try to install langsmith[otel], then set:

  LANGSMITH_OTEL_ENABLED=true
  LANGSMITH_OTEL_ONLY=true            # skip LangSmith writer entirely
  OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318

• LANGSMITH_OTEL_ONLY=true makes the SDK’s background thread bypass the LangSmith ingest path - spans go only to OTLP
  (langsmith/_internal/_background_thread.py::get_tracing_mode, lines 574–594).
• OTEL_EXPORTER_OTLP_ENDPOINT is read before the default LangSmith endpoint is injected (_internal/otel/_otel_client.py::get_otlp_tracer_provider), so your collector
  replaces api.smith.langchain.com/otel. No LANGSMITH_API_KEY required.
• Caveat worth flagging to the OP: LangSmith’s OTEL bridge emits traces only, not OTLP metrics - token/latency data arrives as span attributes. For real metric instruments,
  use the OTEL metrics SDK separately.

Docs: Trace with OpenTelemetry - Docs by LangChain

2 Likes

Hi @pawel-twardziak , Thanks a lot! Your answer works. One thing I see is that environment variable “LANGSMITH_TRACING=true” is still required.
The environment variables I’m using are:

export LANGSMITH_TRACING=true
export LANGSMITH_OTEL_ENABLED=true
export LANGSMITH_OTEL_ONLY=true
export OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318
export LS_APM_OTEL_ENABLED=true
export OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
export OTEL_SERVICE_NAME=mylangchain

1 Like