BlackjackBench and The Thinking Revolution

TL;DR I built BlackjackBench: a Blackjack benchmark covering all 550 initial hands. It can be easily rerun with everything logged and random seeds controllable. Key metric is difference in expected value (ΔEV) compared to the basic‑strategy baseline on the exact same seeded hands. With thinking enabled, models approach baseline: Claude Sonnet 4 (ΔEV ≈ −0.06%, 4.0% mistakes) and GPT‑5 Nano (medium)…