Claude Code doesn’t ship one system prompt with per-model tweaks. It ships two completely different presets, and which one you get is decided by a capability flag on the model. Opus 5 gets the short one (cca 11k chars). Sonnet 5 gets the long one (cca 29k chars). And the long one is where all the anti-verbosity rules live. You can force it. In ~/.claude/settings.json: “env”: { “CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT”: “0” } 0 = force the long preset. 1 = force the short one (no-op on Opus 5, it’s already there). What Opus 5 gets, by default: One line. That’s the entire comment policy: “Write code that reads like the surrounding code: match its comment density, naming, and idiom.” And this is the long preset: Comments: “Default to writing no comments. Only add one when the WHY is non-obvious: a hidden constraint, a subtle invariant, a workaround for a specific bug, behavior that would surprise a reader. If removing the comment wouldn’t confuse a future reader, don’t write it.” “Don’t explain WHAT the code does, since well-named identifiers already do that. Don’t reference the current task, fix, or callers (“used by X”, “added for the Y flow”, “handles the case from issue #123”), since those belong in the PR description and rot as the codebase evolves.” “In code: default to writing no comments. Never write multi-paragraph docstrings or multi-line comment blocks - one short line max.” File spam: “Don’t create planning, decision, or analysis documents unless the user asks for them - work from conversation context, not intermediate files.” “Prefer editing existing files to creating new ones.” Chatter: “Don’t narrate your internal deliberation. User-facing text should be relevant communication to the user, not a running commentary on your thought process.” “End-of-turn summary: one or two sentences. What changed and what’s next. Nothing else.” “Match responses to the task: a simple question gets a direct answer, not headers and sections.” submitted by /u/iviireczech
Originally posted by u/iviireczech on r/ClaudeCode