GPT-5.5 Pro vs DeepSeek-V4

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

DeepSeek-V4

DeepSeek

AI Mastery Index91.8

LMSYS Arena1290

Technical (MMLU-Pro)91.8%

Cost per 1M Tokens$0.14

Architect's Verdict

When comparing GPT-5.5 Pro and DeepSeek-V4, GPT-5.5 Pro edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, DeepSeek-V4 offers a more economical API at $0.14 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.