AI Reports · Epoch AI · 2026-11-04 · Blog / commentary
Updating the ECI methodology to use a Bayesian model
Epoch AI has updated the modeling behind the Epoch Capabilities Index (ECI), which measures and tracks AI model capability using benchmark results. The new Bayesian model aims to provide better-justified uncertainty estimates and to calculate how likely one model is to be more capable than another. The ECI is based on Item Response Theory (IRT), adapted to treat benchmark scores as the expected share of questions a model gets right.