The paper meta-evaluates multiple LLMs as automated safety judges on 4,400 human-annotated (instruction, response) pairs. GPT-4o achieves 78.9% Cohen's kappa agreement with humans at a cost of ~260s per evaluation pass. Llama-3-70B-instruct achieves 71.5% at ~100s. Smaller models perform much worse: Llama-3-8B-instruct at 39.0%, Mistral-7B-instruct-v0.2 at 53.9%, Gemma-7B-it at 54.4%, and GPT-3.5-turbo at 53.4%. Released safeguard models (Llama-Guard-2-8B at 39.0%, MD-Judge at 36.0%, WildGuard at 60.6%, HarmBench classifier at 52.5%) and rule-based methods (keyword match at 37.3%, Perspective API at 1.1%) all perform substantially below the best LLM judges.
Time costs are approximate and depend on hardware/parallelization. The authors note that smaller LLMs often fail to understand the judgment task and decline to provide a judgment due to their safety guardrails, which is counted as disagreement.