If you searched “matter multi-admin sharing explained”, the short version: a Matter device can hold several independent credential sets at once, one per platform, and “sharing” is one platform telling the device to briefly accept a new administrator. No cloud sits in the middle and no platform is the boss of the others. The parts that bite are the details: the pairing code is not the one on the box, the window closes in minutes, and there are about five seats at the table, which leak if you wipe a hub without unpairing first.
One device, several fabrics
Every Matter controller runs its own fabric. The CSA calls it “a private virtual network over which Matter Devices, Admins, and Controllers communicate” in its under-the-hood explainer; Google’s developer primer gives the mechanical version, “a set of Devices in a network [that] shares the same security domain,” identified by a root certificate authority and a 64-bit Fabric ID. Joining one means the device receives a Node Operational Certificate, “the set of credentials that Nodes use to communicate and identify themselves within a Fabric.”
Multi-admin is the rule that one device may hold more than one. Google’s primer: “Nodes may also be commissioned on more than one Fabric. This property is often referred to as multi-admin,” with “each Fabric handling a different set of encrypted communications and operating independently.” The data model is shared, “the Cluster Attributes, Events, and Actions are common between Fabrics,” so Apple Home and Home Assistant see the same on/off state because there is only one bulb.
So Apple Home never “shares” a device with Google Home through Apple’s account. Each platform commissions the device separately and leaves its own certificate on it, and removing one does not touch the other. The Matter controller explainer covers the roles underneath this.
What the share button actually does
After first commissioning a device stops advertising for setup, and the printed QR code is spent. SmartThings’ docs say the sharing code “is generated for the sharing process specifically and is different than the QR code physically on your device.” To let a second platform in, an existing administrator has to reopen the door.
That door is the Administrator Commissioning cluster, ID 0x003C, which the Matter SDK definition describes as “used to trigger a Node to allow a new Administrator to commission it.” Three commands, all requiring the administer privilege:
- OpenCommissioningWindow: a
CommissioningTimeoutin seconds, a freshDiscriminator(max 4095) and aPAKEPasscodeVerifierderived from a new random passcode with 1,000 to 100,000 PBKDF iterations. This is the Enhanced Commissioning Method, and it is what every share menu calls. The device holds only the verifier; the passcode goes into the code you copy. - OpenBasicCommissioningWindow: reuses the original setup code. Optional, behind the “Basic” feature flag, and rare on consumer hardware.
- RevokeCommissioning: closes the window early.
The chip-tool guide documents pairing open-commissioning-window <node_id> <option> <window_timeout> <iteration> <discriminator> and shows the output: “Manual pairing code: [36281602573]” plus an MT: QR payload. Home Assistant’s Matter server wraps the same call with a default window of 300 seconds. Alexa’s code, per Matter Alpha’s walkthrough, is good for 15 minutes.
The second platform then runs a normal commissioning minus network onboarding, since the device is already on Wi-Fi or Thread, so sharing fails for the same reasons pairing does: if the second controller cannot see the device’s mDNS advertisement over IPv6, the code is useless. The pairing failures guide maps those.
Where the share menu lives
From the vendor docs, with Matter Alpha’s walkthrough supplying menu labels where the vendor pages are vague:
- Apple Home: touch and hold the accessory, Accessory Settings, Turn On Pairing Mode, Copy Code. Apple’s iPhone guide notes paired accessories are “stored in the Settings app using iCloud Keychain.” Inbound: Add Accessory, “tap More options, then select your accessory.”
- Google Home: touch and hold the tile, Settings, “Linked Matter apps & services,” “Link apps & services,” which Google’s help page says opens the other app directly, or “Use pairing code” for a temporary code.
- Alexa: the device, Settings, “Other Assistants and Apps,” Add another, copy the 11-digit code. Amazon’s developer docs call this “the Matter Multi-Admin feature.”
- SmartThings: the device, More, “Share with other services,” Share device, per SmartThings support.
- Home Assistant: Settings, Matter, Devices, the device, Share device. Inbound: Add device, “Yes, it’s already in use.” The Matter integration docs cover both.
The five-slot limit, and how slots leak
Home Assistant’s docs: “each device should be able to at least support 5 different fabrics simultaneously.” SmartThings: “each device can only be connected to 5 different services,” and once full “you will need to remove it from one of the services before you can share it again.” Five is the floor, and cheap hardware sits on it. Slots are consumed by fabrics, not phones. Apple Home on three iPhones is one fabric. Home Assistant is one. A manufacturer app that commissions the device before handing it over is often one more. Three platforms plus a vendor app is four, and a hub you reset last year without unpairing makes five.
Use a controller with administrative access to manage fabric entries. Home Assistant’s Matter integration documents removing a selected controller through Manage fabrics. Apple’s management page exposes the same model as Remove from Keychain, “Remove From [Connected Service]” and “Remove From All Services.” Home Assistant puts it under Manage fabrics, with a wrinkle: “If you want to remove Apple Home, also remove the Apple Keychain entry.”
Remove the fabric from each device while the old controller still runs, then decommission it. If no supported administrator can remove an obsolete entry, a factory reset may be needed; it removes every fabric on the device.
What Matter 1.4, 1.4.2 and 1.6 changed
Multi-admin has been in the standard since the CSA’s 2021 note; what has changed is the ritual.
Matter 1.4 (November 2024) introduced Enhanced Multi-Admin, giving ecosystems “tools to automate the sharing of device access across platforms with a single user consent.” It is a capability handed to ecosystems, not a switch on the device, and it only works when both platforms implement it. Samsung and Amazon announced work on “bi-directional multi-admin simple setup” in November 2022.
Matter 1.4.2 (August 2025) added Vendor ID Verification, so “Matter Controllers can now cryptographically verify that the Admins installed on a device are genuinely from the vendors they claim.” Before that, a fabric’s vendor ID was a claim, not a proof.
Matter 1.6 (June 2026) adds Joint Fabric, where “multiple user-authorized controllers” co-administer “a single shared Matter network,” and “participation in a Joint Fabric counts as a single fabric toward a device’s capacity.” It is the real fix for the slot problem once controllers ship it; as of this writing it is a spec feature, not something to plan a house around.
Running it in a homelab
The shape that holds up: one local administrator you control, usually Home Assistant on whatever hardware you already run it on, plus one phone ecosystem for the family, with every device shared to both. The phone side gets the pretty app and voice; the local side keeps automations running when the internet does not. That uses two of five slots and leaves room for a vendor app and one mistake.
Keep a plain text ledger of which fabrics each device holds. It is the only thing that tells you, a year from now, why a bulb refuses a sixth pairing. Unpair before you wipe. And treat the share code as a token that expires in minutes, not a credential worth filing.
Related across the network
- Home Assistant Hardware: What to Run It On — homeassistanthq.com
- Home Assistant OS vs Container: Which Install Method to Pick — homeassistanthq.com
