This is something I was thinking about, too. More than once I've observed a model note in a reasoning trace something along the lines of "this looks like a coding test" (could possibly also refer to leetcode style problems, but same difference). Models often also seem to behave differently in response to one-shot prompts.
On occasions where I let a model do autonomous work, I usually don't just give it a prompt for this reason. I write a CONCEPT.md file, then refine that interactively into a SPEC.md file to find and resolve ambitaskguities (and possibly also create an ARCHITECTURE.md file, if it isn't a one-off ). At this point, most models seem to no longer see it as a benchmark or competitive programming problem, but a proper software engineering task and are less prone to reward hacking (with the caveat that these are very subjective and unfalsifiable impressions).