Verdict
Built from the measurements below
- Accuracy is too close to call: Claude Opus 5.5 scored 85.0% and Muse Spark Open 77.5% on the same 80 questions, a gap within what chance alone could produce.
- Muse Spark Open is 3.2× cheaper per question as billed ($0.0045 vs $0.015), reasoning tokens included.
- Muse Spark Open generates text 1.7× faster: 220 tokens per second against 129.
- Muse Spark Open starts answering sooner: 0.5 s to the first token, against 2.3 s for Claude Opus 5.5.
Which should you choose?
Choose Muse Spark Open for the lower cost per correct answer ($0.0058 against $0.017), faster streaming, a quicker first token and open weights you can run yourself.
Accuracy gap +7.5 points (z = 1.22). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.