[!IMPORTANT] This package is not the latest Langfuse JS/TS SDK. langfuse-core is an internal dependency of the deprecated unscoped v3 client (langfuse). Do not install it for new instrumentation.

Latest JS/TS SDK (OpenTelemetry): npm install @langfuse/tracing @langfuse/otel @opentelemetry/sdk-node. Use @langfuse/tracing (startActiveObservation / startObservation) + LangfuseSpanProcessor from @langfuse/otel. Prompts/datasets/scores: @langfuse/client. Docs: https://langfuse.com/docs/observability/sdk/overview — Upgrade: v3 → v4, v4 → v5.

Query traces with Observations API v2 (GET /api/public/v2/observations, API reference), not GET /api/public/traces / api.traceList.

Data freshness: the only real-time path is OpenTelemetry ingestion (@langfuse/otel, or any OTel exporter sending x-langfuse-ingestion-version: 4) combined with the Observations API v2 and Metrics API v2. All other GET APIs from all SDK packages can be up to 10 minutes behind.

Langfuse Core (legacy v3)

This is the shared core for the legacy Langfuse v3 JS/TS client libraries. It is not meant to be used directly.

Reference: https://js.reference.langfuse.com/modules/langfuse_core.html

Legacy client libraries (do not use for new work)

| Package | NPM | Environments | | ------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------- | --------------------- | | langfuse | | Node >= 18, Web, Edge | | langfuse-node | | Node < 18 | | langfuse-langchain | | Node >= 20, Web, Edge |