Claude Code Rules silently broken since Aug 18 — disable CLAUDE_CODE_THRIFTY_SONIC to fix
4310sy · x · 2026-09-07
Japanese developer kawasin73 documents a silent regression: since 2026-08-18, Claude Code's path-based Rules, Read-triggered Hooks, and subdirectory CLAUDE.md files stopped working. Root cause: the auto-mode system prompt now instructs the model to use Bash (cat/sed/grep) instead of the Read/Edit/Write tools — and path Rules only fire on Read, so the Bash path bypasses rule injection entirely.
Claude Code itself reverse-engineered the bundled source of the installed binary and found the culprit is a feature flag, CLAUDECODETHRIFTYSONIC. Fix: disable it via .claude/settings.. The author verified the flag's impact is limited to that one system-prompt snippet, so disabling it is relatively safe. The article also rejects a PostToolUse(Edit|Write) hook workaround as too late and complex (requires dedup tracking). Broader lesson: silent behavior changes like this will keep happening.
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