No question the capability jump is real, but in my experience it correlates with shortcut-taking. Fable 5 (and Opus 4.8 before it) hallucinates more than any Claude model I’ve used. The most common failure mode is asking it to modify existing code and watching it skip reading the original file, reconstruct that section from imagination, and then apply edits on top of its own invention, even with full context provided.

Maybe my prompts are too vague, but it’s worth noting that every example in the post is a greenfield build, and vague prompting seems to hold up fine when there are no existing constraints to respect.