GPT-5.5 Pro vs GPT-5.6 Terra

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 Terra

OpenAI

AI Mastery Index93.9

LMSYS Arena1470

Technical (MMLU-Pro)93.5%

Cost per 1M Tokens$2.5

Architect's Verdict

When comparing GPT-5.5 Pro and GPT-5.6 Terra, GPT-5.5 Pro edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, GPT-5.6 Terra offers a more economical API at $2.5 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.