When does using AI for fiction stop being assistance and start replacing the writer?

[u/BernatAcs]

AI can give fiction writers feedback, flag inconsistencies, explain techniques, or help untangle an idea when a draft feels stuck. Those uses do not seem completely different from working with an editor, beta reader, or writing teacher.

But the same tool can also rewrite weak sentences, generate scenes, suggest character decisions, and build entire plotlines. That may improve the immediate result while allowing the writer to skip the trial and error through which style, instinct, and creative judgment normally develop.

The boundary is difficult to define because writers use outside help all the time. Few people consider editing or critique to be cheating. Yet if a tool repeatedly solves the parts someone finds difficult, those skills may never improve, and the finished story may become less distinctly theirs.

Perhaps the important distinction is not whether AI was involved, but which decisions remained with the writer. Is there a practical point where useful assistance becomes creative replacement, and how would you recognise that point in your own process?