Configuration guide

Tracing

Send LLM call traces to observability platforms to monitor and evaluate your Nexus deployment

Before you begin

Availability depends on your school's enabled tools, provider setup, and account permissions. These settings are managed in the web workspace. A class policy may restrict a feature described here.

Tracing forwards every LLM call Nexus makes to an external observability platform so you can monitor latency, token usage, and cost, and evaluate response quality. Nexus supports Braintrust and Langfuse.

Tracing is an operator setting. Confirm whether it is configured for your school deployment before relying on it.

Connect a provider#

Navigate to the Tracing dashboard#

Click your user profile icon, select Admin Panel, and open the Tracing tab under the Usage section of the sidebar.

Connect Braintrust and/or Langfuse#

You can connect either or both providers. traces are sent to every connected provider.

Braintrust#

  Create an API key in the [Braintrust dashboard](https://www.braintrust.dev/app) under **Settings → API Keys**.

  In Nexus, click **Connect** on the Braintrust card and fill in:

  * **API Key**. your Braintrust API key.
  * **Project Name** *(optional)*. the Braintrust project traces are logged to. Defaults
    to `Nexus`.
  * **API URL** *(optional)*. only needed for self-hosted Braintrust or non-default
    regions. Defaults to `https://api.braintrust.dev`.

Langfuse#

  Create a key pair in your [Langfuse](https://cloud.langfuse.com) project settings under **Setup → API Keys**.

  In Nexus, click **Connect** on the Langfuse card and fill in:

  * **Secret Key**. your Langfuse secret key (`sk-...`).
  * **Public Key**. your Langfuse public key (`pk-...`).
  * **API Base URL** *(optional)*. defaults to the EU region
    (`https://cloud.langfuse.com`). Set this for the US region, another region, or a self-hosted Langfuse instance.

Nexus validates the credentials before saving. Once connected, the card shows Connected and traces begin flowing within about 30 seconds. no restart required.

Disconnect a provider#

Open the provider card, click the disconnect button, and confirm. Nexus stops sending new traces to that provider immediately. Traces already delivered are unaffected.

Configuring with environment variables#

Configuring tracing from the Admin Panel is the recommended approach, but Nexus also honors environment variables for backwards compatibility. A provider configured through the UI takes precedence over its environment variables.

Provider	Variable	Description
Braintrust	`BRAINTRUST_API_KEY`	API key. Enables Braintrust tracing when set.
Braintrust	`BRAINTRUST_PROJECT`	Project name traces are logged to. Defaults to `Nexus`.
Braintrust	`BRAINTRUST_API_URL`	Custom API URL for self-hosted / non-default regions.
Langfuse	`LANGFUSE_SECRET_KEY`	Secret key. Required (with the public key) to enable Langfuse.
Langfuse	`LANGFUSE_PUBLIC_KEY`	Public key. Required (with the secret key) to enable Langfuse.
Langfuse	`LANGFUSE_HOST`	Base URL for a non-default region or self-hosted Langfuse.

Providers configured through environment variables appear in the Tracing dashboard as configured via environment. You can adopt them into UI-managed configuration by connecting the provider from the Admin Panel.