Verdict
Built from the measurements below
- Accuracy is too close to call: GPT-5.3-Codex scored 82.5% and GPT-6.1 Sol 76.2% on the same 80 questions, a gap within what chance alone could produce.
- GPT-6.1 Sol is 3.6× cheaper per question as billed ($0.0029 vs $0.01), reasoning tokens included.
- GPT-5.3-Codex generates text 2.3× faster: 95 tokens per second against 41.
- GPT-5.3-Codex starts answering sooner: 1.4 s to the first token, against 2.1 s for GPT-6.1 Sol.
- GPT-6.1 Sol accepts more context: 1.1M tokens against 400k.
Which should you choose?
Choose GPT-5.3-Codex for faster streaming and a quicker first token. Choose GPT-6.1 Sol for the lower cost per correct answer ($0.0037 against $0.013), shorter outputs (about 224 tokens per question against 699) and a 1.1M-token context window. The widest subject gap is in medicine: GPT-5.3-Codex answered 7 of 11 correctly, GPT-6.1 Sol 5 of 11. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.
Accuracy gap +6.3 points (z = 0.98). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.