The most private AI is the one that never leaves your phone, and there is a one-minute test for it: turn on airplane mode, open the summarize tool, paste a long email, and ask for three lines. A real answer with no spinner means the work happened on the device in your hand.
A prompt that never travels cannot be intercepted, breached in a server dump, or subpoenaed. That is a real, structural win.
But on-device is not the same as private. Samsung's own notes say its assistant reads your calendar, contacts, call logs, messages, and Gallery, and that some Now Brief content is processed off the device, including by third parties. Apple falls back to a server for larger requests.
Use it, keep the radios off when you can, and do not let "runs on your phone" launder "reads everything on your phone."
