Verdict
Built from the measurements below
- Accuracy is too close to call: GPT-5.3-Codex scored 82.5% and GPT-6 Astra 76.2% on the same 80 questions, a gap within what chance alone could produce.
- GPT-5.3-Codex is 1.3× cheaper per question as billed ($0.01 vs $0.013), reasoning tokens included.
- GPT-5.3-Codex generates text 1.9× faster: 95 tokens per second against 49.
- GPT-6 Astra accepts more context: 1.1M tokens against 400k.
Which should you choose?
Choose GPT-5.3-Codex for the lower cost per correct answer ($0.013 against $0.017) and faster streaming. Choose GPT-6 Astra for shorter outputs (about 205 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.