"Underwater"
Claude Sonnet 3.5.1, #haskell free-form scene description
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It's actually pretty capable. The first images were simple, but had a point. Having seen the result it proposed a few tweaks. And after getting the sources for example scenes and elementary functions it picked up more stuff to its satisfaction.
For the final render I've asked for the corals to be more branchy and that was it. I deliberately didn't suggest anything in implementation or composition to avoid contaminating its idea.
I've been iterating to get an unobstructed camera angle, tweaking a few parameters to my liking, but the bulk of the code it made by itself.