{"version":"2.1.315","anchor":"claude-code-disable-ultrathink-kill-switch","canonical_anchor":"claude-code-disable-ultrathink-kill-switch","heading":"CLAUDE_CODE_DISABLE_ULTRATHINK turns off ultrathink keyword handling","tier":"use","area":"Thinking","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.315\/e\/claude-code-disable-ultrathink-kill-switch","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.315","markdown":"### CLAUDE_CODE_DISABLE_ULTRATHINK turns off ultrathink keyword handling\n\nSetting the new `CLAUDE_CODE_DISABLE_ULTRATHINK` variable stops Claude Code from treating the word ultrathink in your prompt specially\n\n**What**\n\n\"Ultrathink\" is a word you can type in a prompt that Claude Code treats specially. A new environment variable (a named value set outside Claude Code), `CLAUDE_CODE_DISABLE_ULTRATHINK`, turns that handling off.\n\n- When the variable is set, the check `!i.CLAUDE_CODE_DISABLE_ULTRATHINK && v(\"tengu_turtle_carbon\", !0)` returns false, whatever the remote switch `tengu_turtle_carbon` says.\n\n- Claude Code looks for the word ultrathink in your prompt only when that check is true.\n\n- When the variable is unset, nothing changes: the check follows `tengu_turtle_carbon`, which defaults to on.\n\n- The variable is added to several lists of recognised environment variables, including one next to `DISABLE_TELEMETRY` and `CLAUDE_CODE_DISABLE_WEB_FETCH`.\n\nIn readings taken before this release, `tengu_turtle_carbon` came back on for this site's account and on for an anonymous check. No reading has been taken under this release.\n\n**Why**\n\nYou, or an administrator setting up Claude Code for others, can now stop the word ultrathink from triggering its special handling without depending on a remote switch.\n\n- Flag `tengu_turtle_carbon`: On for this account, and not off by default (read for one account on one subscription tier against v2.1.315; this account: on, anonymous baseline: on, compiled default: on) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: Thinking\n- Names: `CLAUDE_CODE_DISABLE_ULTRATHINK`\n- Tier: Use it now\n- Useful: 5\/5\n- Signal: 2\/5\n- Scope: individual\n- Heads-up: no"}