alt Hacker NewsDanluu had an article circulating on HN a few days ago that apparently shows that yes, they can. He implemented Zstd and most models did it almost perfectly in most languages. Pandoc was a challenge they still cold not one shot though, which seems correct to me as the LLM would need proper guidance still for such a large enterprise.
Zstd is decidedly not a "large C application" though, more like a smallish library at best. The C reference implementation is also open source and thus likely part of the training set for coding LLMs. Any model re-implementing Zstd would probably be "remembering" how it was done originally, instead of implementing it from scratch.