GPT-5.5 Pro vs Llama 3.1 405B
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
Llama 3.1 405B
Meta
AI Mastery Index85
LMSYS Arena1255
Technical (MMLU-Pro)88.6%
Cost per 1M Tokens$0
Architect's Verdict
When comparing GPT-5.5 Pro and Llama 3.1 405B, GPT-5.5 Pro edges out in overall capabilities according to the AI Mastery Index. However, for cost-sensitive workloads, Llama 3.1 405B offers a more economical API at $0 per 1M tokens. Your choice should depend heavily on whether you prioritize raw reasoning (MMLU) or scalable deployment economics.