How to turn off Claude Code subagent progress summaries with an environment variable

While a subagent works, Claude Code shows summaries of its progress and sends separate requests to write them. The 2.1.323 changelog lists an environment variable that turns off both the summaries and those requests (the variable has been there since 2.1.318).

export CLAUDE_CODE_DISABLE_AGENT_PROGRESS_SUMMARIES=1

To apply it to every session, put it under env in settings.json.

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_DISABLE_AGENT_PROGRESS_SUMMARIES": "1"
  }
}

Use it when you run many subagents and the extra summary requests add up. The only confirmed value is 1, as written in the changelog; the environment variable docs don't list it yet. On anything older than 2.1.318, run claude update first.