GPT-5.6 Luna vs Gemini 3.1 Ultra

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

GPT-5.6 Luna

OpenAI

AI Mastery Index92

LMSYS Arena1455

Technical (MMLU-Pro)92%

Cost per 1M Tokens$0.2

Gemini 3.1 Ultra

Google

AI Mastery Index92.5

LMSYS Arena1480

Technical (MMLU-Pro)92.5%

Cost per 1M Tokens$20

Architect's Verdict

When comparing GPT-5.6 Luna and Gemini 3.1 Ultra, Gemini 3.1 Ultra 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.