Opus 5 beats Fable on benchmarks but loses badly in real use, analyst says

petergyang · x · 2026-07-26

The quoted analysis argues that current public benchmarks are becoming nearly useless for judging frontier models.
It claims Opus 5 looks much weaker than Fable in real use, even though Opus wins on many benchmarks.
The takeaway is that domain-specific evals built on private datasets may become more trustworthy than public leaderboards.
It also suggests Anthropic may be training the 5-series differently from earlier Sonnet/Opus generations, though the post truncates before the full comparison.

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