GPT-5.5 Pro vs Claude Opus 4.8

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

Claude Opus 4.8

Anthropic

AI Mastery Index94.6

LMSYS Arena1362

Technical (MMLU-Pro)94.5%

Cost per 1M Tokens$15

Architect's Verdict

When comparing GPT-5.5 Pro and Claude Opus 4.8, Claude Opus 4.8 edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, Claude Opus 4.8 offers a more economical API at $15 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.