This is quite puzzling. Back in the day I saw the breakthrough with Opus 4.5, and since then was very lightweight on CLAUDE.md, trying to declare intent, rather than prescribe imperative instructions. If it was off the mark, I would see clear mismatch, which gave me opportunity to correct, usually to clear and strip context.

Starting with Fable 5, if it goes off the rails, it is more difficult to correct it, because it is overall wrong, but covers its tracks with plausible sounding arguments, so it is hard to pin point and correct.

Now, this article points out techniques that were useful to rely on models more, but those peaked at 4.6. Now according to benchmarks Opus 5 is on the frontier. But when when it has looser reigns, it ends up gaslighting me even more with abstract word soup than any model before.