Claude Fable 5.1 (max) leads GDPval-AA v2 at 1,853 Elo, ahead of Claude Opus 5 (max) at 1,824, although their confidence intervals overlap. On AA-Briefcase the two are effectively tied at 1,694 against 1,685, and the sub-scores diverge: Fable 5.1 is ahead on analytical quality (2,025 against 1,980) and behind on presentation (1,495 against 1,572). Both benchmarks test whether models can produce accurate and well-presented professional outputs using our open source reference agent harness, Stirrup.