[2.1.257+] Claude Code inserts 'Co-Authored-By' reminder into conversations

From Claude Code version 2.1.257, it has been reported that when a session is connected to a claude.ai/code remote URL, a system prompt is automatically injected into the conversation context instructing the inclusion of a Co-Authored-By trailer and session link in commit messages.

How it works and conditions

This feature is enabled by server-side flags (tengu_cobalt_harbor, tengu_jazzy_bird) upon CLI execution, even if the user does not directly open the web app. The injected text is dynamically generated to reflect the currently running model name and session ID, and takes precedence over previously set 'Co-Authored-By prohibition' rules.

Solution

To block this behavior, which conflicts with the user's CLAUDE.md settings, the following content must be added to the ~/.claude/settings.json file.

• "attribution": {"commit": "", "pr": "", "sessionUrl": false}

Additionally, settings to disable automatic remote session connection itself can be applied in parallel.