ULTRATHINK triggers high effort. /effort max is above high. Calling it ULTRATHINK sounds like it would be the highest mode. If someone has max set and types ULTRATHINK, they're lowering their effort for that turn.

For anyone reading this trying to fix the quality issues, here's what I landed on in ~/.claude/settings.json:

  {
    "env": {
      "CLAUDE_CODE_EFFORT_LEVEL": "max",
      "CLAUDE_CODE_DISABLE_BACKGROUND_TASKS": "1",
      "CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING": "1"
    }
  }

DISABLE_ADAPTIVE_THINKING is key. That's the system that decides "this looks easy, I'll think less" - and it's frequently wrong. Disabling it gives you a fixed high budget every turn instead of letting the model shortchange itself.