Astra leads in mathematics but not in software engineering
A domain breakdown of the capabilities index showed GPT-6 Astra setting a record in mathematics while trailing Claude Fable 5.1 on software engineering.
Why it matters
An independent index showed the newest frontier model is not ahead everywhere, which contradicts the single-number framing that accompanies releases.
The publication is dated 16 September 2026. On the general Epoch Capabilities Index, GPT-6 Astra takes first place with 166.31, ahead of Claude Fable 5.1 at 164.47 and GPT-5.6 Sol at 161.81. On the mathematics component Astra scores 169.83, the highest measured, ahead of Claude Fable 5.1 at 165.73 and GPT-5.6 Sol at 162.76. On the software engineering component Astra scores 163.58 against 167.44 for Claude Fable 5.1, trailing by about 3.9 points.