[!IMPORTANT] This package is not the latest Langfuse JS/TS SDK. npm install langfuse installs a deprecated v3 client (new Langfuse(), trace(), span(), api.traceList). Do not use 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 — Legacy Langfuse v3 SDK (maintenance mode)

This package is the legacy v3 SDK. It is in maintenance mode and only receives critical bug fixes. The current Langfuse JS/TS SDK lives in the scoped @langfuse/* packages.

Use the current SDK instead

npm install @langfuse/tracing @langfuse/otel @opentelemetry/sdk-node
# Optional: prompts, datasets, scores, REST API
npm install @langfuse/client

| Current package | Use for | Replaces (v3) | | ---------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------- | ------------------------------------ | | @langfuse/tracing | OpenTelemetry-based tracing (startActiveObservation / startObservation) | langfuse.trace() / .generation() | | @langfuse/otel | LangfuseSpanProcessor to export OTel spans to Langfuse | event ingestion in langfuse | | @langfuse/client | Prompts, datasets, scores, and other Langfuse API access | langfuse.getPrompt(), api.* | | @langfuse/openai | OpenAI SDK auto-instrumentation | observeOpenAI from langfuse | | @langfuse/langchain | LangChain callback handler | langfuse-langchain | | @langfuse/vercel-ai-sdk | Vercel AI SDK v7 integration (AI SDK ≤6: experimental_telemetry + @langfuse/otel) | langfuse-vercel |

• Docs (current SDK): https://langfuse.com/docs/observability/sdk/overview
• Upgrade path: v3 → v4, v4 → v5

Legacy v3 documentation

This is the legacy JS/TS client for Langfuse v3. Prefer the current SDK above for new work.

Documentation

• Legacy docs: https://langfuse.com/docs/sdk/typescript
• Current SDK docs: https://langfuse.com/docs/observability/sdk/overview
• Reference: https://js.reference.langfuse.com/modules/langfuse.html

Environments

Supported

• Node.js >=18
• Web
• Edge: Vercel, Cloudflare Workers, etc.

Using Node.js <18? Use langfuse-node instead as it does not use fetch and other Web APIs

Installation (legacy v3 only)

Only install this package to maintain an existing v3 integration:

npm i langfuse
# or
yarn add langfuse
# or
pnpm i langfuse