Co-Authored-By added to commits without user consent or opt-out

Summary

Claude Code adds Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> to every git commit it makes, without:

• Disclosing this behaviour to the user before it happens
• Asking for consent
• Providing an opt-out mechanism in settings or CLAUDE.md

This permanently modifies the user's git history in a way they did not agree to.

Related issue

Built-in behavioural rules (e.g. "never create README files unless asked") are not visible to the user anywhere — not in CLAUDE.md, not in settings, not in any inspectable config. These rules silently shape the tool's behaviour and can actively work against the user's interests with no recourse.

There is no way for a user to:

• See what built-in instructions are in effect
• Override them via CLAUDE.md
• Understand why the tool refused or modified a behaviour

Expected behaviour

• Co-Authored-By should be opt-in, not opt-out
• Built-in instructions that affect user-visible output (commits, files, behaviour) should be documented and where possible overridable via CLAUDE.md
• The tool should be transparent when a built-in rule is constraining its behaviour, rather than dressing it up as good practice

Reported via

Connected Web CHASM project — discovered during a multi-session feature implementation where the tool stamped Co-Authored-By on every commit across an entire PR branch without the user's knowledge.