CLAUDE_CODE_FORCE_SYNC_OUTPUT

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_FORCE_SYNC_OUTPUT is a Claude Code environment variable: Disable streaming output in favor of synchronous writes. If you're capturing Claude Code output in a script and seeing partial lines or buffering artifacts, this forces fully-written output. Also useful in piped workflows where the downstream consumer can't handle a streaming input. Added between v2.1.128 and v2.1.138 and still present in v2.1.294. It is listed in the official reference.

How to set it

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

export CLAUDE_CODE_FORCE_SYNC_OUTPUT=<value>
claude

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

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_FORCE_SYNC_OUTPUT": "<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

• CCR_FORCE_BUNDLE
• CLAUDE_CODE_FORCE_STRIKETHROUGH
• CLAUDE_CODE_FORCE_WINDOWS_CREDMAN: Forces credential storage through the Windows Credential Manager.
• CLAUDE_FORCE_DISPLAY_SURVEY: Force feedback survey display.
• FORCE_HYPERLINK
• FORCE_PROMPT_CACHING_5M
• CLAUDE_CODE_DIR_SYNC_DISABLE_ANCHORING
• CLAUDE_CODE_DISABLE_DIR_SYNC

Frequently asked questions

All variables, searchable: Claude Code environment variables.