You might have noticed that Opus 5 is extremely eager to talk. It is like the uncle at the family party who always has an overly long, boring story about literally anything, and no request is too small to set one off.
Ask said uncle for a one-line change and you'll get the long history of why the code needed changing, why he never spotted it sooner, how it was not his change in the first place, and how this whole thing reminds him of a story... which was the right call, mind you, and here is how you might approach the problem next time. Your CLAUDE.md has said Be concise. No preamble. near the top for a year. On 4.x it mostly listened. On 5 the line is still sitting there, in the same file, in the same position, and the model reads straight past it.
I gave someone four paths for this in a Reddit thread. Here they are again, weakest lever first.
CLAUDE.md instructions
Write the rule down first. It is the obvious move and the weakest one. Be concise on its own barely registers, because it names nothing the model can act on. A rule that names the shape you want does better. Here is the one I use for reply verbosity, paste-ready for your own CLAUDE.md:
