Claude Mythos Preview vs Qwen3.5 397B

Pick Claude Mythos Preview if you want the stronger benchmark profile. Qwen3.5 397B only becomes the better choice if you want the cheaper token bill or you would rather avoid the extra latency and token burn of a reasoning model.

Claude Mythos Preview is clearly ahead on the aggregate, 84 to 70. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.

Claude Mythos Preview's sharpest advantage is in agentic, where it averages 80.9 against 52.5. The single biggest benchmark swing on the page is HLE, 64.7% to 28.7%.

Claude Mythos Preview is also the more expensive model on tokens at $25.00 input / $125.00 output per 1M tokens, versus $0.00 input / $0.00 output per 1M tokens for Qwen3.5 397B. That is roughly Infinityx on output cost alone. Claude Mythos Preview is the reasoning model in the pair, while Qwen3.5 397B 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. Claude Mythos Preview gives you the larger context window at 1M, compared with 128K for Qwen3.5 397B.