Verdict
GPT-5.6 Sol leads 6–2 across 10 shared benchmarks.
GPT-5.5 Pro 2 · GPT-5.6 Sol 6 · 2 tied · higher isn't always better — check the caveats below.
Reported scores — protocols may differ. How we compare
Reasoning: Evenly split 2–2 across 4 shared reasoning benchmarks (largest gap: SimpleQA Verified, 71.6 vs 64.5 — single evaluator).
Math: GPT-5.6 Sol leads 1–0 across 2 shared math benchmarks (largest gap: FrontierMath-Tier-4-v2-Private, 82.93 vs 78.05 — single evaluator).
Vendor claims — compare against the measured scores above. A claim is what a developer says about its own model, not an independent measurement.
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”
Reasoning
“GPT-5.5 Pro, designed for even harder questions and higher-accuracy work, is available to Pro, Business, and Enterprise users.”
Writing
“testers found GPT-5.5 Pro's responses significantly more comprehensive, well-structured, accurate, relevant, and useful”
No vendor claims on file for GPT-5.6 Sol.
GPT-5.6 Sol leads 6–2 across 10 shared benchmarks. GPT-5.5 Pro leads 2 benchmarks and GPT-5.6 Sol leads 6, with 2 tied. Higher isn't always better — see the integrity caveats on each benchmark.
GPT-5.5 Pro and GPT-5.6 Sol have 10 benchmarks in common in our data — those are the only rows where a direct, apples-to-apples comparison is drawn.
GPT-5.6 Sol leads math 1–0.