Assuming /effort max still gets the best performance out of the model (meaning "ULTRATHINK" is still a step below /effort max, and equivalent to /effort high), here is what I landed on when trying to get Opus 4.7 to be at peak performance all the time in ~/.claude/settings.json:

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

The env field in settings.json persists across sessions without needing /effort max every time.

I don't like how unpredictable and low quality sub agents are, so I like to disable them entirely with disable_background_tasks.