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HomeDocsClaude Code CLI 14 Oct 2026
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Modifying system prompts changedagent-sdk/modifying-system-prompts

Nearest release: v2.1.300, published 7 hours before upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Upstream edited this page at 14 Oct 2026 21:42 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 14 Oct 2026 22:07 UTC.

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389389## Context Claude Code adds outside the system prompt
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391System reminders are messages Claude Code adds to the conversation during a session to give Claude context, such as the contents of your CLAUDE.md files or a note that a file changed on disk. Claude Code sends them in the conversation, not in the system prompt, so they reach Claude whether you use the `claude_code` preset or pass your own string as `systemPrompt`.
391System reminders are messages Claude Code adds to the conversation during a session to give Claude context, such as the contents of your CLAUDE.md files or a note that a file changed on disk. Claude Code sends them in the conversation, not in the system prompt, so most reach Claude whether you use the `claude_code` preset or pass your own string as `systemPrompt`.
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393393This section covers the [reminders most likely to change how your agent behaves](#reminders-claude-code-adds-to-the-conversation), how to [turn off the ones your agent replaces](#turn-off-the-context-your-agent-replaces), and how to [see what Claude received](#see-what-claude-received) in a specific request.
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427427| Every CLAUDE.md file | Set `CLAUDE_CODE_DISABLE_CLAUDE_MDS=1` |
428428| Task list nudges, file-changed notes, and the skill list | Set `CLAUDE_CODE_DISABLE_ATTACHMENTS=1` |
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430Claude Code's built-in commit and pull request instructions aren't a reminder. They are part of the Bash tool's description, so they also reach Claude when you pass a custom `systemPrompt`.
430Set `includeGitInstructions` to `false` to keep out the built-in commit and pull request instructions, which are part of the Bash tool's description and reach Claude even with a custom `systemPrompt`. With the minimal default, a custom `systemPrompt`, or a custom main-thread agent that has its own prompt, though, the session starts without the git status snapshot.
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432432If you set `CLAUDE_CODE_DISABLE_ATTACHMENTS`, Claude Code also sends `@` file mentions as plain text instead of expanding them into file content. The list of available subagents and background task notifications still arrive. To stop only `@` file mentions from expanding, set [`CLAUDE_CODE_DISABLE_FILE_MENTIONS=1`](/docs/en/env-vars#variables) instead, on Claude Code v2.1.299 or later. Claude then gets the mentioned paths plus a note to read them with its file tools.
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