🪢 Langfuse OpenTelemetry Integration

The Langfuse OpenTelemetry integration allows you to send LiteLLM traces and observability data to Langfuse using the OpenTelemetry protocol. This provides a standardized way to collect and analyze your LLM usage data.

Features

• Automatic trace collection for all LiteLLM requests
• Support for Langfuse Cloud (EU and US regions)
• Support for self-hosted Langfuse instances
• Custom endpoint configuration
• Secure authentication using Basic Auth
• Consistent attribute mapping with other OTEL integrations

Prerequisites

1. Langfuse Account: Sign up at Langfuse Cloud or set up a self-hosted instance
2. API Keys: Get your public and secret keys from your Langfuse project settings
3. Dependencies: Install required packages:

   uv add litellm opentelemetry-api opentelemetry-sdk opentelemetry-exporter-otlp
   

Configuration

Environment Variables

Endpoint Resolution

The integration automatically constructs the OTEL endpoint from LANGFUSE_OTEL_HOST

• Default (US): https://us.cloud.langfuse.com/api/public/otel
• EU Region: https://cloud.langfuse.com/api/public/otel
• Self-hosted: {LANGFUSE_OTEL_HOST}/api/public/otel

Usage

Basic Setup

# Set your Langfuse credentials
os.environ["LANGFUSE_PUBLIC_KEY"] = "pk-lf-..."
os.environ["LANGFUSE_SECRET_KEY"] = "sk-lf-..."

# Enable Langfuse OTEL integration
litellm.callbacks = ["langfuse_otel"]

# Make LLM requests as usual
response = litellm.completion(
    model="gpt-3.5-turbo",
    messages=[{"role": "user", "content": "Hello!"}]
)

Advanced Configuration

# Set your Langfuse credentials
os.environ["LANGFUSE_PUBLIC_KEY"] = "pk-lf-..."
os.environ["LANGFUSE_SECRET_KEY"] = "sk-lf-..."

# Use EU region
os.environ["LANGFUSE_OTEL_HOST"] = "https://cloud.langfuse.com"  # EU region
# os.environ["LANGFUSE_OTEL_HOST"] = "https://otel.my-langfuse.company.com"  # custom OTEL endpoint

# Or use self-hosted instance
# os.environ["LANGFUSE_OTEL_HOST"] = "https://my-langfuse.company.com"

# Optional: Ignore otel context propagation to prevent parent-child relationships with spans from other providers
# os.environ["OTEL_IGNORE_CONTEXT_PROPAGATION"] = "true"

litellm.callbacks = ["langfuse_otel"]

Manual OTEL Configuration

If you need direct control over the OpenTelemetry configuration:

# Get keys for your project from the project settings page: https://cloud.langfuse.com
os.environ["LANGFUSE_PUBLIC_KEY"] = "pk-lf-..." 
os.environ["LANGFUSE_SECRET_KEY"] = "sk-lf-..." 
os.environ["LANGFUSE_OTEL_HOST"] = "https://cloud.langfuse.com" # EU region
# os.environ["LANGFUSE_OTEL_HOST"] = "https://us.cloud.langfuse.com" # US region
# os.environ["LANGFUSE_OTEL_HOST"] = "https://otel.my-langfuse.company.com" # custom OTEL endpoint

LANGFUSE_AUTH = base64.b64encode(
    f"{os.environ.get('LANGFUSE_PUBLIC_KEY')}:{os.environ.get('LANGFUSE_SECRET_KEY')}".encode()
).decode()

host = os.environ.get("LANGFUSE_OTEL_HOST")
os.environ["OTEL_EXPORTER_OTLP_ENDPOINT"] = host + "/api/public/otel"
os.environ["OTEL_EXPORTER_OTLP_HEADERS"] = f"Authorization=Basic {LANGFUSE_AUTH}"

litellm.callbacks = ["langfuse_otel"]

With LiteLLM Proxy

Add the integration to your proxy configuration:

1. Add the credentials to your environment variables

# export LANGFUSE_OTEL_HOST="https://otel.my-langfuse.company.com"  # custom OTEL endpoint

# Optional: Ignore otel context propagation to prevent parent-child relationships with spans from other providers
# export OTEL_IGNORE_CONTEXT_PROPAGATION="true"

2. Setup config.yaml

# config.yaml
litellm_settings:
  callbacks: ["langfuse_otel"]

3. Run the proxy

litellm --config /path/to/config.yaml

Data Collected

The integration automatically collects the following data:

• Request Details: Model, messages, parameters (temperature, max_tokens, etc.)
• Response Details: Generated content, token usage, finish reason
• Timing Information: Request duration, time to first token
• Metadata: User ID, session ID, custom tags (if provided)
• Error Information: Exception details and stack traces (if errors occur)

Metadata Support

All metadata fields available in the vanilla Langfuse integration are now fully supported when you use the OTEL integration.

• Any key you pass in the metadata dictionary (generation_name, trace_id, session_id, tags, and the rest) is exported as an OpenTelemetry span attribute.
• Attribute names are prefixed with langfuse. so you can filter or search for them easily in your observability backend. Examples: langfuse.generation.name, langfuse.trace.id, langfuse.trace.session_id.

Passing Metadata – Example

response = litellm.completion(
    model="gpt-3.5-turbo",
    messages=[{"role": "user", "content": "Hello!"}],
    metadata={
        "generation_name": "welcome-message",
        "trace_id": "trace-123",
        "session_id": "sess-42",
        "tags": ["prod", "beta-user"]
    }
)

The resulting span will contain attributes similar to:

langfuse.generation.name   = "welcome-message"
langfuse.trace.id          = "trace-123"
langfuse.trace.session_id  = "sess-42"
langfuse.trace.tags        = ["prod", "beta-user"]

Use the Langfuse UI (Traces tab) to search, filter and analyse spans that contain the langfuse.* attributes. The OTEL exporter in this integration sends data directly to Langfuse’s OTLP HTTP endpoint; it is not intended for Grafana, Honeycomb, Datadog, or other generic OTEL back-ends.

Authentication

The integration uses HTTP Basic Authentication with your Langfuse public and secret keys:

Authorization: Basic <base64(public_key:secret_key)>

This is automatically handled by the integration - you just need to provide the keys via environment variables.

Troubleshooting

Common Issues

1. Missing Credentials Error

   ValueError: LANGFUSE_PUBLIC_KEY and LANGFUSE_SECRET_KEY must be set
   

   Solution: Ensure both environment variables are set with valid keys.

2. Connection Issues

   • Check your internet connection
   • Verify the endpoint URL is correct
   • For self-hosted instances, ensure the /api/public/otel endpoint is accessible

3. Authentication Errors

   • Verify your public and secret keys are correct
   • Check that the keys belong to the same Langfuse project
   • Ensure the keys have the necessary permissions

Debug Mode

Enable verbose logging to see detailed information:

litellm._turn_on_debug()

This will show:

• Endpoint resolution logic
• Authentication header creation
• OTEL trace submission details

Related Links

• Langfuse Documentation
• Langfuse OpenTelemetry Guide
• OpenTelemetry Python SDK
• LiteLLM Observability