Claude Mythos 5 vs GPT-4.1 nano

Pick Claude Mythos 5 if you want the stronger benchmark profile. GPT-4.1 nano 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 5 is clearly ahead on the provisional aggregate, 99 to 26. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.

Claude Mythos 5's sharpest advantage is in knowledge, where it averages 74.6 against 50.3. The single biggest benchmark swing on the page is GPQA, 94.1% to 50.3%.

Claude Mythos 5 is also the more expensive model on tokens at $10.00 input / $50.00 output per 1M tokens, versus $0.10 input / $0.40 output per 1M tokens for GPT-4.1 nano. That is roughly 125.0x on output cost alone. Claude Mythos 5 is the reasoning model in the pair, while GPT-4.1 nano 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 5 gives you the larger context window at 1M+, compared with 1M for GPT-4.1 nano.