Clean Engineering, Unstable Measurement: A Preregistered Reliability Failure of Black-Box LLM Observers on Shared Endpoints
By Haoyaun Zhu, Jie Zhang
A pre-registered reliability audit of black-box LLM judges across 52,988 request attempts finds that same-window repeat rankings agree at Spearman 0.400 (required 0.90) and byte-identical next-day replays agree at 0.78 (required 0.99), despite execution records being at ceiling. The paper attributes the gap to biased label-to-meaning mappings, candidate gaps far below instrument resolution, and protocol-specific effects.