Mistral Medium 3.5 vs Qwen3.5 397B A17B: accuracy, speed and price

• Accuracy is too close to call: Mistral Medium 3.5 scored 28.8% and Qwen3.5 397B A17B 32.5% on the same 80 questions, a gap within what chance alone could produce.
• Qwen3.5 397B A17B is 1.9× cheaper per question as billed ($0.013 vs $0.025), reasoning tokens included.
• Qwen3.5 397B A17B generates text 1.7× faster: 240 tokens per second against 145.
• Mistral Medium 3.5 starts answering sooner: 0.5 s to the first token, against 0.6 s for Qwen3.5 397B A17B.

Which should you choose?

Choose Mistral Medium 3.5 for a quicker first token. Choose Qwen3.5 397B A17B for the lower cost per correct answer ($0.041 against $0.087), faster streaming, open weights you can run yourself and more hosts to choose from on OpenRouter (10 against 1). The widest subject gap is in science: Qwen3.5 397B A17B answered 10 of 30 correctly, Mistral Medium 3.5 5 of 30. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.

Accuracy gap -3.8 points (z = -0.51). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.