Verdict
Built from the measurements below
- Accuracy is too close to call: Claude Opus 5.5 scored 85.0% and Gemini 3.8 Flash 82.5% on the same 80 questions, a gap within what chance alone could produce.
- Gemini 3.8 Flash is 4.0× cheaper per question as billed ($0.0037 vs $0.015), reasoning tokens included.
- Output speed is similar (129 vs 142 tokens per second).
- Claude Opus 5.5 starts answering sooner: 2.3 s to the first token, against 3.2 s for Gemini 3.8 Flash.
Which should you choose?
Choose Claude Opus 5.5 for a quicker first token and more hosts to choose from on OpenRouter (5 against 2). Choose Gemini 3.8 Flash for the lower cost per correct answer ($0.0045 against $0.017).
Accuracy gap +2.5 points (z = 0.43). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.