The Epoch Capabilities Index (ECI) is Epoch AI’s composite measure that combines frontier models’ scores across many benchmarks into one capability scale, published with CC-BY data and a public repository (index page). The corpus first cites it for the finding that frontier improvement rates nearly doubled after April 2024 on the shift to reasoning, and returns to it in April 2026 when Claude Mythos’s benchmark sweep registered as an apparent upward discontinuity on the index.
Benchmark
Epoch Capabilities Index
Epoch AI's composite index that places frontier models on a single capability scale across benchmarks, the yardstick the corpus uses for the post-April-2024 acceleration and later discontinuities.
Sources
Attribution and reporting linked by this record; links do not imply independent verification.
- Welcome to December 24, 2025 (theinnermostloop.substack.com)
Development timeline
Newest reporting dates first. Reporting dates may differ from event dates.
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