Matter fabric & multi-admin
A Matter fabric is one ecosystem’s trust domain: the set of devices and controllers sharing security credentials, such as your Apple Home. Multi-admin is the Matter feature that lets a single device join several fabrics at once — the same plug can live in Apple Home and Google Home simultaneously, each with local control, no re-pairing.
When you commission a device, the controller installs its fabric’s certificate on the device. Multi-admin works by having the first ecosystem open a temporary commissioning window and hand you a fresh pairing code (“share” or “pair with another app” in most apps); the second ecosystem then adds its own credentials alongside the first. The spec requires devices to support at least five fabrics.
Multi-admin is genuinely useful in mixed households — iPhone and Android, or Alexa voice with Apple automations — because each fabric talks to the device directly and locally, not through the other ecosystem’s cloud. The limits: automations and scenes do not sync across fabrics (each ecosystem keeps its own), and removing the device from one fabric leaves the others intact, which occasionally surprises people expecting a factory reset.