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The arize-phoenix-evals library uses an LLM-as-judge to grade model output — hallucinations, factuality, helpfulness, toxicity, custom rubrics. Phoenix Evals does not ship a native Mistral adapter, so plug Mistral in via the LiteLLM proxy by passing provider="litellm" and model="mistral/<model-id>" to the LLM(...) wrapper, then build a create_classifier(...) evaluator and run it over a DataFrame with evaluate_dataframe(...).

Prerequisites

Install

litellm is the proxy that routes the eval calls to Mistral. You don’t need the mistralai SDK installed separately.

Configure credentials

LiteLLM reads MISTRAL_API_KEY from the environment when it sees a mistral/... model id.

Setup the eval LLM

mistral-large-latest is a strong default judge; for cheaper batch evals swap in mistral/mistral-small-latest. The judge’s job is classification, not generation, so a smaller model is often sufficient.

Run an evaluation

This example builds a hallucination classifier and grades two sample question/answer pairs against a reference. The pattern generalizes: replace the prompt template, choices, and DataFrame columns with whatever metric you want to evaluate.

Expected output

The full returned DataFrame also includes hallucination_execution_details (status + exceptions + timing) and the original hallucination_score column with each evaluator result’s full dict (name, score, label, explanation, metadata, kind, direction) — useful for surfacing the LLM’s reasoning, persisting eval rows back to Arize AX, or filtering retries.

Troubleshooting

  • 401 / 403 from Mistral. Verify MISTRAL_API_KEY is set and has access to the model. Generate a new key at console.mistral.ai.
  • model_not_found or 404. Confirm the model id is correct — LiteLLM expects mistral/<id> (e.g. mistral/mistral-large-latest, mistral/mistral-small-latest). See the LiteLLM Mistral provider docs for the current list.
  • All rows return the same label. Your prompt template isn’t differentiating cases. Make sure each row’s {input}/{output}/{reference} columns expose enough context for the judge to discriminate, and that choices lists every label your prompt asks the LLM to emit.
  • Some rows fail with timeout / rate-limit. Pass max_retries= to evaluate_dataframe(...) (defaults to 3). For large batches, also pass initial_per_second_request_rate=... to LLM(...) to throttle.
  • Logging results back to Arize AX. This guide stops at producing the eval DataFrame. To attach those evals to existing spans in an Arize AX project, use log_evaluations_sync on arize.Client.
  • Using a different LiteLLM-supported provider. Swap the mistral/... prefix for any LiteLLM-supported modelprovider="litellm" is the generic escape hatch when no native Phoenix adapter exists.

Resources

Phoenix Evals Documentation

arize-phoenix-evals on PyPI

Phoenix Evals Source

Mistral AI Tracing (instrument app calls)