Verdict
Built from the measurements below
- Accuracy is too close to call: GPT-5.3-Codex scored 82.5% and GPT-6.1 Terra Pro 76.2% on the same 80 questions, a gap within what chance alone could produce.
- GPT-6.1 Terra Pro is 2.1× cheaper per question as billed ($0.005 vs $0.01), reasoning tokens included.
- GPT-5.3-Codex starts answering sooner: 1.4 s to the first token, against 8.5 s for GPT-6.1 Terra Pro.
- GPT-6.1 Terra Pro accepts more context: 1.1M tokens against 400k.
Which should you choose?
Choose GPT-5.3-Codex for a quicker first token. Choose GPT-6.1 Terra Pro for the lower cost per correct answer ($0.0065 against $0.013), shorter outputs (about 453 tokens per question against 699) and a 1.1M-token context window.
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.