CLAUDE_CODE_MID_CONVERSATION_SYSTEM

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_MID_CONVERSATION_SYSTEM is a Claude Code environment variable: Inject a system message mid-conversation. Your harness can update Claude's constraints, inject new context, or shift behavioral guidelines without ending the session. Removed between v2.1.143 and v2.1.212, so current releases ignore it. It is not in the official reference.

How to set it

For one session, export it in the shell that starts Claude Code:

export CLAUDE_CODE_MID_CONVERSATION_SYSTEM=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_MID_CONVERSATION_SYSTEM": "<value>"
  }
}

Release notes that mention it

• Claude Code v2.1.143 — 27 New Env Vars, /goal, Agent View, and a Free Model Upgrade

Related variables

• CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT: Switches to a reduced system prompt, stripping out the non-essential guidance sections that bulk up the default prompt.
• CLAUDE_CODE_SYSTEM_PROMPT_GB_FEATURE: Names a GrowthBook feature flag whose value overrides the system prompt — but only when CLAUDE_CODE_REMOTE is set.
• ANTHROPIC_BETAS: Comma-separated beta feature headers.
• ANTHROPIC_CUSTOM_HEADERS: Custom HTTP headers (newline-separated Key: Value).
• ANTHROPIC_FEDERATION_RULE_ID
• ANTHROPIC_ORGANIZATION_ID
• ANTHROPIC_WORKSPACE_ID
• BETA_TRACING_ENDPOINT: Custom endpoint for beta tracing.

Frequently asked questions

All variables, searchable: Claude Code environment variables.