GPT-5.5 Pro vs Llama 3.1-405B
Verdict
GPT-5.5 Pro leads 3–0 across 3 shared benchmarks.
GPT-5.5 Pro 3 · Llama 3.1-405B 0 · higher isn't always better — see caveats.
Per-benchmark head-to-head
Reported scores — protocols may differ. How we compare
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GPT-5.5 ProLlama 3.1-405B
Capabilities
Reasoning
Reasoning: GPT-5.5 Pro leads 2–0 across 2 shared reasoning benchmarks (largest gap: SimpleBench, 72.28 vs 7.6 — single evaluator).
2 reproduced2 unverified
What the labs claim
Vendor claims — compare against the measured scores above. A claim is what a developer says about its own model, not an independent measurement.
GPT-5.5 Pro
General
“In GPT-5.5 Pro, early testers are seeing a significant step up in both the difficulty and quality of work ChatGPT can take on”
openai.com2026
Reasoning
“GPT-5.5 Pro, designed for even harder questions and higher-accuracy work, is available to Pro, Business, and Enterprise users.”
openai.com2026
Writing
“testers found GPT-5.5 Pro's responses significantly more comprehensive, well-structured, accurate, relevant, and useful”
openai.com2026
Llama 3.1-405B
Context Handling
“These are multilingual and have a significantly longer context length of 128K, state-of-the-art tool use, and overall stronger reasoning capabilities.”
ai.meta.com2024
General
“Llama 3.1 405B is in a class of its own, with unmatched flexibility, control, and state-of-the-art capabilities that rival the best closed source models.”
ai.meta.com2024“Llama 3.1 405B is the first openly available model that rivals the top AI models when it comes to state-of-the-art capabilities in general knowledge, steerability, math, tool use”
ai.meta.com2024