Verdict
Built from the measurements below
- Accuracy is too close to call: Hermes 4 405B scored 26.2% and Mistral Medium 3.5 28.8% on the same 80 questions, a gap within what chance alone could produce.
- Hermes 4 405B is 2.5× cheaper per question as billed ($0.01 vs $0.025), reasoning tokens included.
- Mistral Medium 3.5 generates text 3.6× faster: 145 tokens per second against 41.
- Hermes 4 405B starts answering sooner: 0.3 s to the first token, against 0.5 s for Mistral Medium 3.5.
- Mistral Medium 3.5 accepts more context: 262k tokens against 131k.
Which should you choose?
Choose Hermes 4 405B for the lower cost per correct answer ($0.038 against $0.087), a quicker first token and open weights you can run yourself. Choose Mistral Medium 3.5 for faster streaming and a 262k-token context window.
Accuracy gap -2.5 points (z = -0.35). We call a winner only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.