Verdict
Built from the measurements below
- Accuracy is too close to call: Claude Sonnet 5.5 scored 78.8% and Muse Spark Open 77.5% on the same 80 questions, a gap within what chance alone could produce.
- Muse Spark Open is 1.2× cheaper per question as billed ($0.0045 vs $0.0054), reasoning tokens included.
- Muse Spark Open generates text 1.7× faster: 220 tokens per second against 126.
- Muse Spark Open starts answering sooner: 0.5 s to the first token, against 0.7 s for Claude Sonnet 5.5.
Which should you choose?
Choose Claude Sonnet 5.5 for shorter outputs (about 456 tokens per question against 964). Choose Muse Spark Open for the lower cost per correct answer ($0.0058 against $0.0069), faster streaming, a quicker first token and open weights you can run yourself.
Accuracy gap +1.2 points (z = 0.19). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.