Langfuse JS/TS SDKs
langfuse-js
Modular mono repo for the Langfuse JS/TS client libraries.
Packages
The SDK was rewritten in v5 and released in March 2026. Refer to the v5 migration guide for instructions on updating your code.
langfuse on npm is not the latest Langfuse JS/TS SDK. The unscoped packages langfuse, langfuse-core, langfuse-node, and langfuse-langchain are the deprecated v3 client (new Langfuse(), trace(), span(), api.traceList). Do not npm install langfuse for new instrumentation.
Latest install: 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.
| Package | NPM | Description | Environments |
|---|---|---|---|
| @langfuse/client |  |
Langfuse API client for universal JavaScript environments | Universal JS |
| @langfuse/browser |  |
Langfuse browser SDK for public-key score ingestion | Browser |
| @langfuse/tracing |  |
Langfuse instrumentation methods based on OpenTelemetry | Node.js 20+ |
| @langfuse/otel |  |
Langfuse OpenTelemetry export helpers | Node.js 20+ |
| @langfuse/openai |  |
Langfuse integration for OpenAI SDK | Universal JS |
| @langfuse/langchain |  |
Langfuse integration for LangChain | Universal JS |
| @langfuse/vercel-ai-sdk |  |
Langfuse integration for AI SDK v7 | Universal JS |
Documentation
Development
This is a monorepo managed with pnpm. See CONTRIBUTING.md for detailed development instructions.
Quick start:
pnpm install # Install dependencies
pnpm build # Build all packages
pnpm test # Run tests
pnpm ci # Run full CI suite