Verdict
Built from the measurements below
- Accuracy is too close to call: Claude Fable 5.1 scored 81.2% and Grok 4.7 80.0% on the same 80 questions, a gap within what chance alone could produce.
- Claude Fable 5.1 is 1.6× cheaper per question as billed ($0.016 vs $0.025), reasoning tokens included.
- Output speed is similar (70 vs 77 tokens per second).
- Grok 4.7 starts answering sooner: 1.9 s to the first token, against 2.1 s for Claude Fable 5.1.
- Claude Fable 5.1 accepts more context: 1M tokens against 500k.
Which should you choose?
Choose Claude Fable 5.1 for the lower cost per correct answer ($0.02 against $0.031), shorter outputs (about 238 tokens per question against 3,952), a 1M-token context window and more hosts to choose from on OpenRouter (4 against 1). Choose Grok 4.7 for a quicker first token.
Accuracy gap +1.2 points (z = 0.20). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.