be7aSystem Card: Claude Mythos Preview [pdf]
https://www-cdn.anthropic.com/53566bf5440a10affd749724787c8913a2ae0841.pdf
Combined results (Claude Mythos / Claude Opus 4.6 / GPT-5.4 / Gemini 3.1 Pro)
SWE-bench Verified: 93.9% / 80.8% / — / 80.6%
SWE-bench Pro: 77.8% / 53.4% / 57.7% / 54.2%
SWE-bench Multilingual: 87.3% / 77.8% / — / —
SWE-bench Multimodal: 59.0% / 27.1% / — / —
Terminal-Bench 2.0: 82.0% / 65.4% / 75.1% / 68.5% GPQA Diamond: 94.5% / 91.3% / 92.8% / 94.3%
MMMLU: 92.7% / 91.1% / — / 92.6–93.6%
USAMO: 97.6% / 42.3% / 95.2% / 74.4%
GraphWalks BFS 256K–1M: 80.0% / 38.7% / 21.4% / —
HLE (no tools): 56.8% / 40.0% / 39.8% / 44.4%
HLE (with tools): 64.7% / 53.1% / 52.1% / 51.4%
CharXiv (no tools): 86.1% / 61.5% / — / —
CharXiv (with tools): 93.2% / 78.9% / — / —
OSWorld: 79.6% / 72.7% / 75.0% / —
Honestly we are all sleeping on GPT-5.4. Particularly with the influx of Claude users recently (and increasingly unstable platform) Codex has been added to my rotation and it's surprising me.
GPT is shit at writing code. It's not dumb - extra high thinking is really good at catching stuff - but it's like letting a smart junior into your codebase - ignore all the conventions, surrounding context, just slop all over the place to get it working. Claude is just a level above in terms of editing code.
Very different experience for me. Codex 5.3+ on xhigh are the only models I've tried so far that write reasonably decent C++ (domains: desktop GUI, robotics, game engine dev, embedded stuff, general systems engineering-type codebases), and idiomatic code in languages not well-represented in training data, e.g. QML. One thing I like is explicitly that it knows better when to stop, instead of brute-forcing a solution by spamming bespoke helpers everywhere no rational dev would write that way.
Not always, no, and it takes investment in good prompting/guardrails/plans/explicit test recipes for sure. I'm still on average better at programming in context than Codex 5.4, even if slower. But in terms of "task complexity I can entrust to a model and not be completely disappointed and annoyed", it scores the best so far. Saves a lot on review/iteration overhead.
It's annoying, too, because I don't much like OpenAI as a company.
(Background: 25 years of C++ etc.)