Verdict
Built from the measurements below
- Accuracy is too close to call: GPT-5.4 scored 72.5% and GPT-6 Luna 72.5% on the same 80 questions, a gap within what chance alone could produce.
- GPT-6 Luna is 46× cheaper per question as billed ($0.00025 vs $0.011), reasoning tokens included.
- GPT-6 Luna generates text 2.5× faster: 137 tokens per second against 55.
- GPT-6 Luna starts answering sooner: 1.2 s to the first token, against 1.7 s for GPT-5.4.
Which should you choose?
Choose GPT-6 Luna for the lower cost per correct answer ($0.00034 against $0.016), faster streaming, a quicker first token and shorter outputs (about 431 tokens per question against 706). The widest subject gap is in medicine: GPT-6 Luna answered 6 of 11 correctly, GPT-5.4 4 of 11. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.
Accuracy gap +0.0 points (z = 0.00). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.