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Pairing a Mac

A phone can hold a 4B model. A Mac can hold something far larger. Pairing the two puts your Mac's models in your phone's model picker, and the phone's size limits stop applying.

This is one of only two features that can send anything off your phone. The Mac reads your prompt in order to answer it — which is not the same as the prompt never leaving. It goes to a second machine you own, over your own network, through no infrastructure of ours.

Pairing

  1. On the Mac, open the Elythros Mac app and turn on sharing. It displays a pairing code.
  2. On the iPhone, go to Settings → Mac offload and choose your Mac from the list.
  3. Type the code once. When the iPhone connects, the code disappears.

To pair another iPhone, choose Pair another iPhone on the Mac. Each phone gets its own code and its own key, never shared, and the Mac lists every phone paired with it. Removing one stops it connecting straight away.

That is the whole relationship. There is no account, nothing to sign up for, and no list of your devices held anywhere except on the Mac itself — not by us.

Pair where you would be willing to type a password. Anyone who can read the code off the Mac's screen as you type it can pose as your phone.

Using it

Once paired, the Mac's models appear in the model picker under On your Mac. Choose one and that conversation's messages are answered there. Choose a local model and nothing leaves the phone.

The phone remembers the pairing. When you open the app it reconnects on its own — you do not need to visit the pairing screen again.

Download the model on the Mac first

The Mac answers with models it has, not ones your phone has. If you select a Mac model the Mac has not downloaded, the first prompt triggers a multi-gigabyte download before anything is generated.

Download what you want on the Mac before you rely on it from the phone.

How the connection is secured

The pairing code is a 32-byte key that becomes a TLS pre-shared key. Both ends derive the connection from those bytes independently, so a wrong code produces no shared secret at all and the connection dies inside the handshake, before a single byte of your prompt is read. Each iPhone has its own key, so one phone cannot pose as your Mac to another.

Inside that tunnel, every connection performs its own HPKE key exchange (RFC 9180) over a hybrid of X25519 and ML-KEM-768. The keys exist only in memory and die with the connection, so traffic recorded today stays unreadable to someone who obtains your pairing code tomorrow — or to a quantum computer later. The pairing key is mixed into that exchange's keys as well, so a session opens only between the two devices holding that pairing.

The security page describes this in full, including what it does not protect against.

Networking details

The Mac advertises itself over Bonjour on the local network, which is why discovery works where broadcast does — the same network. The service listens on port 42217 by default.

To reach a Mac that discovery cannot see, see reaching it from anywhere.