Claude Sonnet 4.5 vs Mistral Medium 3.5 128B

Pick Mistral Medium 3.5 128B if you want the stronger benchmark profile. Claude Sonnet 4.5 only becomes the better choice if you would rather avoid the extra latency and token burn of a reasoning model.

Mistral Medium 3.5 128B is clearly ahead on the provisional aggregate, 78 to 64. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.

Mistral Medium 3.5 128B's sharpest advantage is in coding, where it averages 77.6 against 77.2. The single biggest benchmark swing on the page is SWE-bench Verified, 77.2% to 77.6%.

Claude Sonnet 4.5 is also the more expensive model on tokens at $3.00 input / $15.00 output per 1M tokens, versus $1.50 input / $7.50 output per 1M tokens for Mistral Medium 3.5 128B. That is roughly 2.0x on output cost alone. Mistral Medium 3.5 128B is the reasoning model in the pair, while Claude Sonnet 4.5 is not. That usually helps on harder chain-of-thought-heavy tests, but it can also mean more latency and more token spend in real use. Mistral Medium 3.5 128B gives you the larger context window at 256K, compared with 200K for Claude Sonnet 4.5.