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OpenAI's cheapest tier cut its price 61%, cut its hallucination rate from 93% to 77%, and lost a point on the independent index. Same-harness data on both generations, where Luna regressed, where it improved, and the ten-week price collapse.
Opus 5.5 matches GPT-6 Astra on Terminal-Bench 4.0 for roughly 40% of the cost per task, with 5x cheaper cache reads. Astra keeps uncontested leads in science, maths and gated offensive security — and OpenAI says it is harder to monitor.