GPT-5.5 Pro vs GPT-4o

Head-to-head technical comparison of intelligence, capabilities, and API pricing.

GPT-5.5 Pro

OpenAI

AI Mastery Index94.2

LMSYS Arena1350

Technical (MMLU-Pro)94.2%

Cost per 1M Tokens$30

GPT-4o

OpenAI

AI Mastery Index87.2

LMSYS Arena1287

Technical (MMLU-Pro)88.7%

Cost per 1M Tokens$5

Architect's Verdict

When comparing GPT-5.5 Pro and GPT-4o, GPT-5.5 Pro edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, GPT-4o offers a more economical API at $5 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.