The Epoch Capabilities Index (ECI) is a composite metric that integrates scores from 39 AI benchmarks into a unified scale for evaluating and comparing model capabilities over time. Utilizing Item Response Theory, the ECI provides a statistical framework to assess model performance against benchmark difficulty, allowing for consistent scoring of AI models such as Claude 3.5 and GPT-5. Future details on the methodology will be published in an upcoming paper funded by Google DeepMind.