Verdict
Built from the measurements below
- Accuracy is too close to call: GPT-5.3-Codex scored 82.5% and GPT-6 Sol 73.8% on the same 80 questions, a gap within what chance alone could produce.
- GPT-6 Sol is 4.4× cheaper per question as billed ($0.0024 vs $0.01), reasoning tokens included.
- Output speed is similar (95 vs 92 tokens per second).
- GPT-6 Sol starts answering sooner: 0.9 s to the first token, against 1.4 s for GPT-5.3-Codex.
- GPT-6 Sol accepts more context: 1.1M tokens against 400k.
Which should you choose?
Choose GPT-6 Sol for the lower cost per correct answer ($0.0032 against $0.013), a quicker first token, shorter outputs (about 174 tokens per question against 699) and a 1.1M-token context window. The widest subject gap is in engineering: GPT-5.3-Codex answered 11 of 15 correctly, GPT-6 Sol 8 of 15. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.
Accuracy gap +8.7 points (z = 1.34). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.