GPT-5.5 Pro vs GPT-5.6 Luna

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

GPT-5.5 Pro

OpenAI

AI Mastery Index94.2

LMSYS Arena1468

Technical (MMLU-Pro)94.2%

Cost per 1M Tokens$30

GPT-5.6 Luna

OpenAI

AI Mastery Index92

LMSYS Arena1455

Technical (MMLU-Pro)92%

Cost per 1M Tokens$0.2

Architect's Verdict

When comparing GPT-5.5 Pro and GPT-5.6 Luna, GPT-5.5 Pro edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, GPT-5.6 Luna offers a more economical API at $0.2 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.