Verdict
Built from the measurements below
- Accuracy is too close to call: Gemini 4 Argon scored 84.8% and Muse Spark Open 77.5% on the same 79 questions, a gap within what chance alone could produce.
- Muse Spark Open is 1.4× cheaper per question as billed ($0.0045 vs $0.0063), reasoning tokens included.
- Muse Spark Open generates text 3.2× faster: 220 tokens per second against 69.
- Muse Spark Open starts answering sooner: 0.5 s to the first token, against 3.3 s for Gemini 4 Argon.
Which should you choose?
Choose Gemini 4 Argon for shorter outputs (about 558 tokens per question against 964). Choose Muse Spark Open for the lower cost per correct answer ($0.0058 against $0.0074), faster streaming, a quicker first token, open weights you can run yourself and more hosts to choose from on OpenRouter (6 against 2). The widest subject gap is in law: Gemini 4 Argon answered 6 of 6 correctly, Muse Spark Open 4 of 6. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.
Accuracy gap +7.3 points (z = 1.18). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.