Verdict
Built from the measurements below
- Accuracy is too close to call: Claude Opus 5.5 scored 85.0% and Grok 4.7 80.0% on the same 80 questions, a gap within what chance alone could produce.
- Claude Opus 5.5 is 1.7× cheaper per question as billed ($0.015 vs $0.025), reasoning tokens included.
- Claude Opus 5.5 generates text 1.7× faster: 129 tokens per second against 77.
- Grok 4.7 starts answering sooner: 1.9 s to the first token, against 2.3 s for Claude Opus 5.5.
- Claude Opus 5.5 accepts more context: 1M tokens against 500k.
Which should you choose?
Choose Claude Opus 5.5 for the lower cost per correct answer ($0.017 against $0.031), faster streaming, shorter outputs (about 645 tokens per question against 3,952), a 1M-token context window and more hosts to choose from on OpenRouter (5 against 1). Choose Grok 4.7 for a quicker first token.
Accuracy gap +5.0 points (z = 0.83). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.