Look at GPT 5.6-Sol vs. GPT 5.6-Luna in particular.
(The GLM pair shouldn't be expected follow this pattern, because they're misnamed: GLM-5.3 and GLM-5.3-flash are distinct lineages. The -flash is an early release of a new pretrain on a new architecture).
If this *is* the main factor, I'd expect Kimi K3.1 and Gemini Carbon would also do well on this test (unlike Gemini-flash); while Haiku 6 would collapse (breaking the trend of the other recent Claude models). It's a falsifiable prediction.
>When we read the trajectories, we saw that many models had figured out they were in a benchmark and started second-guessing the prompt. Instead of just building what we asked for, they started coding to the tests they thought the grader would run.
I ran into the same problem on my English exams.
For my use case deepseek 4.1 flash is almost as dumb as haiku 5.5. Both are fast garbage producers.
I have access to Claude Code at work (and use it quite a bit), so I feel I can honestly compare them.
You do have to plan things first a bit more with DS (than say Opus can, although it often over-engineers and tries to be too helpful in my experience) and be a bit more explicit at times, but I feel it's quite close to Sonnet in performance for implementing plans and for debugging issues.
Moreover, the months I've used anthropic/OAI exclusively my API token costs are in the hundreds (or sometimes thousands). With DS flash as the first agent I reach for, I rarely exceed $40/mo.
I mean of course, the real world is messy, the models are only good for what they've been trained on, and post-training frequently takes benchmark scores into account too, leading to this sort of "Great score, sucks in the real world" syndrome that seemingly most models are affected by.
Edit: another comment pointed out it's probably not benchmaxxing due to the chronology.
https://news.ycombinator.com/item?id=50406948
But why should minor changes to the task cause catastrophic performance drops? How is that not evidence of benchmaxxing?