“Frontier AI systems have surpassed the self-replicating red line” is the sort of title you give a preprint for clickbait potential. An LLM, a spicy autocomplete, can now produce copies of itself! …
I am not a coder at all, but I think it would be pretty damn trivial to give software the ability to replicate itself considering worms have literally been around since the Internet Worm in 1988. RTM was by no means an AI coder.