Broadcast to Langfuse - Send Traces to Langfuse

Langfuse is an open-source LLM engineering platform for tracing, evaluating, and debugging LLM applications.

Step 1: Create a Langfuse API key

In Langfuse, go to your project’s Settings > API Keys and create a new key pair. Copy both the Secret Key and Public Key.

Step 2: Enable Broadcast in OpenRouter

Go to Settings > Observability and toggle Enable Broadcast.

Step 3: Configure Langfuse

Click the edit icon next to Langfuse and enter:

Secret Key: Your Langfuse Secret Key
Public Key: Your Langfuse Public Key
Base URL (optional): Default is https://us.cloud.langfuse.com. Change for other regions or self-hosted instances

Step 4: Test and save

Click Test Connection to verify the setup. The configuration only saves if the test passes.

Step 5: Send a test trace

Make an API request through OpenRouter and view the trace in Langfuse.

Custom Metadata

Langfuse supports rich trace hierarchies and metadata. Use the trace field to customize how your traces appear in Langfuse.

Supported Metadata Keys

Key	Langfuse Mapping	Description
`trace_id`	Trace ID	Group multiple requests into a single trace
`trace_name`	Trace Name	Custom name displayed in the Langfuse trace list
`span_name`	Span Name	Name for intermediate spans in the hierarchy
`generation_name`	Generation Name	Name for the LLM generation observation
`parent_span_id`	Parent Observation ID	Link to an existing span in your trace hierarchy
`environment`	Environment	Populates the first-class `Environment` field used by the Langfuse project filter (e.g. `production`, `staging`). Emitted as both a resource attribute and observation attribute.
`release`	Release	Application release/version associated with the trace. Emitted as both a resource attribute and observation attribute.

Example

{
  "model": "openai/gpt-4o",
  "messages": [{ "role": "user", "content": "Summarize this document..." }],
  "user": "user_12345",
  "session_id": "session_abc",
  "trace": {
    "trace_id": "workflow_12345",
    "trace_name": "Document Processing Pipeline",
    "span_name": "Summarization Step",
    "generation_name": "Generate Summary",
    "environment": "production",
    "release": "2.1.0",
    "pipeline_version": "2.1.0"
  }
}

This creates a hierarchical trace structure in Langfuse:

Document Processing Pipeline (trace)
└── Summarization Step (span)
    └── Generate Summary (generation)

Additional Context

The user field maps to Langfuse’s User ID for user-level analytics
The session_id field maps to Langfuse’s Session ID for grouping conversations
Any additional keys in trace are passed as trace metadata and can be used for filtering and analysis in Langfuse

Privacy Mode

When Privacy Mode is enabled for this destination, prompt and completion content is excluded from traces. All other trace data — token usage, costs, timing, model information, and custom metadata — is still sent normally. See Privacy Mode for details.

​Step 1: Create a Langfuse API key

​Step 2: Enable Broadcast in OpenRouter

​Step 3: Configure Langfuse

​Step 4: Test and save

​Step 5: Send a test trace

​Custom Metadata

​Supported Metadata Keys

​Example

​Additional Context

​Privacy Mode