Epoch's new SpireClimb benchmark found GPT-6.1 Sol achieved a 20% win rate at Slay the Spire 1's maximum difficulty, Ascension 20 Heart, with GPT-6 Astra reaching 17%. Frontier models beat base difficulty at least 90% of the time, versus near-zero six months ago. Anthropic reported Claude Fable 5 reached the final act three times more often than Claude Opus 4.8. METR's Ajeya Cotra uses win rates in capability forecasts.
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