Public Benchmarks: What They Measure and Where They Fail

~30 min read

Critical guide to MMLU, HellaSwag, HumanEval, and LMSYS Arena — saturation, contamination, and how to use them correctly.

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Key points

  • MMLU and HellaSwag are saturated at the top — differences < 3% between top models are noise, not signal
  • HumanEval has known contamination from GitHub Copilot training data; treat scores with skepticism
  • LMSYS Chatbot Arena Elo is the most reliable public signal for instruction-following, but biased toward English chat