Beta LangSmith Collector-Proxy

This is a beta feature. The API may change in future releases.

The LangSmith Collector-Proxy is a lightweight, high-performance proxy server that sits between your application and the LangSmith backend. It batches and compresses trace data before sending it to LangSmith, reducing network overhead and improving performance.

When to Use the Collector-Proxy

The Collector-Proxy is particularly valuable when:

• You’re running multiple instances of your application in parallel and need to efficiently aggregate traces
• You want more efficient tracing than direct OTEL API calls to LangSmith (the collector optimizes batching and compression)
• You’re using a language that doesn’t have a native LangSmith SDK

Key Features

• Efficient Data Transfer Batches multiple spans into fewer, larger uploads.
• Compression Uses zstd to minimize payload size.
• OTLP Support Accepts OTLP JSON and Protobuf over HTTP POST.
• Semantic Translation Maps GenAI/OpenInference conventions to the LangSmith Run model.
• Flexible Batching Flush by span count or time interval.

Configuration

Configure via environment variables:

Variable	Description	Default
HTTP_PORT	Port to run the proxy server	4318
LANGSMITH_ENDPOINT	LangSmith backend URL	https://api.smith.langchain.com
LANGSMITH_API_KEY	API key for LangSmith	Required (env var or header)
LANGSMITH_PROJECT	Default tracing project	Default project if not specified
BATCH_SIZE	Spans per upload batch	100
FLUSH_INTERVAL_MS	Flush interval in milliseconds	1000
MAX_BUFFER_BYTES	Max uncompressed buffer size	10485760 (10 MB)
MAX_BODY_BYTES	Max incoming request body size	209715200 (200 MB)
MAX_RETRIES	Retry attempts for failed uploads	3
RETRY_BACKOFF_MS	Initial backoff in milliseconds	100

Project Configuration

The Collector-Proxy supports LangSmith project configuration with the following priority:

1. If a project is specified in the request headers (Langsmith-Project), that project will be used
2. If no project is specified in headers, it will use the project set in the LANGSMITH_PROJECT environment variable
3. If neither is set, it will trace to the default project.

Authentication

The API key can be provided either:

• As an environment variable (LANGSMITH_API_KEY)
• In the request headers (X-API-Key)

Deployment (Docker)

You can deploy the Collector-Proxy with Docker:

1. Build the image

   docker build \
     -t langsmith-collector-proxy:beta .
   

2. Run the container

   docker run -d \
     -p 4318:4318 \
     -e LANGSMITH_API_KEY=<your_api_key> \
     -e LANGSMITH_PROJECT=<your_project> \
     langsmith-collector-proxy:beta
   

Usage

Point any OTLP-compatible client or the OpenTelemetry Collector exporter at:

export OTEL_EXPORTER_OTLP_ENDPOINT=http://<host>:4318/v1/traces
export OTEL_EXPORTER_OTLP_HEADERS="X-API-Key=<your_api_key>,Langsmith-Project=<your_project>"

Send a test trace:

curl -X POST http://localhost:4318/v1/traces \
  -H "Content-Type: application/json" \
  --data '{
    "resourceSpans": [
      {
        "resource": {
          "attributes": [
            {
              "key": "service.name",
              "value": { "stringValue": "test-service" }
            }
          ]
        },
        "scopeSpans": [
          {
            "scope": {
              "name": "example/instrumentation",
              "version": "1.0.0"
            },
            "spans": [
              {
                "traceId": "T6nh/mMkIONaoHewS9UWIw==",
                "spanId": "0tEqJwCpvU0=",
                "name": "parent-span",
                "kind": "SPAN_KIND_INTERNAL",
                "startTimeUnixNano": 1747675155185223936,
                "endTimeUnixNano":   1747675156185223936,
                "attributes": [
                  {
                    "key": "gen_ai.prompt",
                    "value": {
                      "stringValue": "{\"text\":\"Hello, world!\"}"
                    }
                  },
                  {
                    "key": "gen_ai.usage.input_tokens",
                    "value": {
                      "intValue": "5"
                    }
                  },
                  {
                    "key": "gen_ai.completion",
                    "value": {
                      "stringValue": "{\"text\":\"Hi there!\"}"
                    }
                  },
                  {
                    "key": "gen_ai.usage.output_tokens",
                    "value": {
                      "intValue": "3"
                    }
                  }
                ],
                "droppedAttributesCount": 0,
                "events": [],
                "links": [],
                "status": {}
              }
            ]
          }
        ]
      }
    ]
  }'

Health & Scaling

• Liveness: GET /live → 200
• Readiness: GET /ready → 200

Horizontal Scaling

To ensure full traces are batched correctly, route spans with the same trace ID to the same instance (e.g., via consistent hashing).

Fork & Extend

Fork the Collector-Proxy repo on GitHub and implement your own converter:

• Create a custom GenAiConverter or modify the existing one in internal/translator/otel_converter.go
• Register the custom converter in internal/translator/translator.go

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