> ## Documentation Index
> Fetch the complete documentation index at: https://opentouter.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Braintrust
> Send traces to Braintrust
[Braintrust](https://www.braintrust.dev) is an end-to-end platform for evaluating, monitoring, and improving LLM applications.
## Step 1: Get your Braintrust API key and Project ID
In Braintrust, go to your [Account Settings](https://www.braintrust.dev/app/settings) to create an API key, and find your Project ID in your project's settings.
## Step 2: Enable Broadcast in OpenRouter
Go to [Settings > Observability](https://openrouter.ai/settings/observability) and toggle **Enable Broadcast**.
## Step 3: Configure Braintrust
Click the edit icon next to **Braintrust** and enter:
* **Api Key**: Your Braintrust API key
* **Project Id**: Your Braintrust project ID
* **Base Url** (optional): Default is `https://api.braintrust.dev`
## 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 Braintrust.
## Custom Metadata
Braintrust supports custom metadata, tags, and nested span structures for organizing your LLM logs.
### Supported Metadata Keys
| Key | Braintrust Mapping | Description |
| ----------------- | ---------------------- | ------------------------------------------------ |
| `trace_id` | Span ID / Root Span ID | Group multiple logs into a single trace |
| `trace_name` | Name | Custom name displayed in the Braintrust log view |
| `span_name` | Name | Name for intermediate spans in the hierarchy |
| `generation_name` | Name | Name for the LLM span |
### Example
```json lines theme={null}
{
"model": "openai/gpt-4o",
"messages": [{ "role": "user", "content": "Generate a summary..." }],
"user": "user_12345",
"session_id": "session_abc",
"trace": {
"trace_id": "eval_run_456",
"trace_name": "Summarization Eval",
"generation_name": "GPT-4o Summary",
"eval_dataset": "news_articles",
"experiment_id": "exp_789"
}
}
```
### Metrics and Costs
Braintrust receives detailed metrics for each LLM call:
* Token counts (prompt, completion, total)
* Cached token usage when available
* Reasoning token counts for supported models
* Cost information (input, output, total costs)
* Duration and timing metrics
### Additional Context
* The `user` field maps to Braintrust's `user_id` in metadata
* The `session_id` field maps to `session_id` in metadata
* Custom metadata keys are included in the span's metadata object
* Tags are passed through for filtering in the Braintrust UI
## Privacy Mode
When [Privacy Mode](/guides/features/broadcast#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](/guides/features/broadcast#privacy-mode) for details.