OpenAI's GPT-6 Astra tops the Epoch Capabilities Index (ECI) with a score of 166, ahead of Claude Fable 5.1 at 164 and GPT-5.6 Sol at 162. Its Math-ECI of 170 sets a new record, but on software engineering benchmarks its SWE-ECI of 164 still lags behind Fable 5.1's 167.

Expert assessments and cyber benchmarks led us to expect that frontier models were capable of executing this kind of cyberattack

Compiling all the public evidence on Mythos Preview’s cyber abilities

Relative to their general Epoch Capabilities Index (ECI) values, Anthropic’s Claude models overperform on software engineering benchmarks (aggregated by the SWE-ECI) and underperform on math (Math-ECI). The SWE overperformance has been consistent across most generations, and remains in recent models. The math gap may be narrowing — Opus 4.6 and 4.7 both have Math-ECIs within 1 point of their general ECI, compared to larger gaps for earlier models.

We investigate progress trends on four capability metrics to determine whether AI capabilities have recently accelerated. Three of four metrics show strong evidence of acceleration, driven by reasoning models.