GPT-5.5 Pro achieves a new high score on the ECI

GPT-5.5 Pro achieves a new high score of 159 on the Epoch Capabilities Index — our statistical tool that combines multiple benchmarks into a unified scale.

GPT-5.5 Pro also set new records on FrontierMath, scoring 52% on Tiers 1-3 (up from 50%) and 40% on Tier 4 (up from 38%). Across runs, it and GPT-5.5 solved two Tier 4 problems that no model had solved before, one by Hailong Dao and one by Ahsan Khan (@ahsanxrr). They had this to say:

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