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Weights & Biases Weave is an observability platform for tracking and evaluating LLM applications.

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Step 1: Get your W&B API key

In W&B, go to your User Settings and copy your API key.

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Step 2: Enable Broadcast in OpenRouter

Go to Settings > Observability and toggle Enable Broadcast.
Enable Broadcast

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Step 3: Configure W&B Weave

Click the edit icon next to W&B Weave and enter:
  • Api Key: Your W&B API key
  • Entity: Your W&B username or team name
  • Project: The project name where traces will be logged
  • Base Url (optional): Default is https://trace.wandb.ai
W&B Weave Configuration

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Step 4: Test and save

Click Test Connection to verify the setup. The configuration only saves if the test passes.
W&B Weave Configured

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Step 5: Send a test trace

Make an API request through OpenRouter and view the trace in W&B Weave.
W&B Weave Trace

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Custom Metadata

W&B Weave supports custom attributes and structured inputs for organizing and analyzing your LLM calls.

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Supported Metadata Keys

KeyWeave MappingDescription
trace_idopenrouter_trace_id attributeCustom trace identifier stored in attributes
trace_nameop_nameCustom operation name displayed in the Weave call list
generation_nameop_nameName for the LLM call

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Example

{
  "model": "openai/gpt-4o",
  "messages": [{ "role": "user", "content": "Write a poem about AI..." }],
  "user": "user_12345",
  "session_id": "session_abc",
  "trace": {
    "trace_name": "Creative Writing Agent",
    "prompt_template": "poem_v2",
    "experiment_name": "creative_benchmark",
    "dataset_version": "1.0.0"
  }
}

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Attributes and Inputs

Weave organizes trace data into:
  • Attributes: Metadata about the call (user IDs, organization IDs, trace identifiers, custom metadata)
  • Inputs: The actual request data including messages, model parameters (temperature, max_tokens, etc.)
  • Summary: Token usage, costs, and timing metrics

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Additional Context

  • The user field maps to user_id in attributes
  • The session_id field maps to session_id in attributes
  • Custom metadata keys from trace are merged into the call’s attributes
  • Model parameters (temperature, max_tokens, top_p) are included in inputs for easy filtering

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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.