June 2026

Local vs cloud AI writing: the privacy difference

Every AI writing tool needs your text to make a suggestion. The only real question is where that text goes. Cloud tools send it to a server. Local tools keep it on your Mac. That single choice decides everything about your privacy.

What “cloud” actually means here

With a cloud writing assistant, the words around your cursor are packaged up and sent to a remote server every time it wants to predict what comes next. The model runs there, and a suggestion comes back. That means your half-written email, your Slack reply, your private notes — the raw text — travels over the network to a company you don't control.

Most of the time that's fine in theory. But the text is now off your machine. It can be logged, retained for “model improvement,” subpoenaed, or exposed in a breach. Even with a good privacy policy, you're trusting a promise rather than a fact.

What “local” means instead

A local, on-device tool runs the model on your own hardware. On Apple Silicon, that's fast enough to finish a sentence as you type. MacAutocomplete works this way: an MLX model lives on your Mac, so the prediction happens right where you're typing — the rest of the sentence appears as ghost text and you press ⇥ Tab to accept it. Nothing is sent anywhere to make that happen.

There's zero outbound network for completions. Password and secure-input fields are never read in the first place. The full story is on how private and local it stays.

The difference, side by side

You can verify local — you can't verify cloud

This is the part that matters. A cloud tool's privacy is a claim you can't check. A local tool's privacy is something you can prove in a minute: open Little Snitch, start typing, and watch for outbound connections — there are none for completions. Or just turn off Wi-Fi and keep writing. If the suggestions still appear, the model is genuinely on your Mac.

Local doesn't mean limited

On-device used to mean weak word-level guesses. That's no longer true — the model predicts whole phrases and sentences across Mail, Slack, Notes, Messages, and most browser fields. It's honest about its dead zones too: the Google Docs and Sheets canvas, some GPU- or canvas-based editors, and games sit outside the text fields the system exposes. If you're comparing on-device options, the MacAutocomplete vs Cotypist breakdown covers where they line up and where they part ways.

Cloud or local, you're going to type your private thoughts into this thing all day. The only version where that text never leaves your Mac is the local one — and it's the only version you can actually verify.