The short answer: routing is not controlling
A Thread border router forwards IPv6 traffic between the low-power Thread mesh and the home's Wi-Fi or Ethernet network. It does not decide what a lock, sensor, light, or plug should do. A Matter controller commissions the accessory into an ecosystem, holds permissions, and exposes controls and automations. Matter-over-Thread normally needs both roles, even when one physical hub supplies them.
Matter-over-Wi-Fi needs a controller but not Thread
A Matter accessory can communicate over Wi-Fi, Ethernet, or Thread. A Matter-over-Wi-Fi plug still needs a Matter controller or hub for the chosen ecosystem, but it does not need a Thread border router for its radio path. The Matter logo alone therefore does not tell you which network hardware is required; check the transport named on the box and current product page.
Exact generation beats the family name
Apple lists HomePod mini, HomePod (2nd generation), Apple TV 4K (2nd generation), and Apple TV 4K (3rd generation) Wi-Fi + Ethernet as Thread-enabled devices. Google lists Nest Hub (2nd generation), Nest Hub Max, Nest Wifi Pro, and Google TV Streamer (4K) among its Thread border routers, while Nest Hub (1st generation) remains a Matter hub without Thread. Similar names do not guarantee the same radio.
A combined hub can still leave two separate Thread networks
Buying a second border router does not automatically extend the first Thread mesh. Ecosystems may create separate Thread networks with different credentials, and multi-admin sharing controls the Matter fabric rather than magically merging every Thread credential set. Choose the primary ecosystem, verify credential sharing, and commission one accessory before resetting an existing installation.
Write both requirements before purchase
For a Matter-over-Thread device, write down the exact accessory model and transport, the primary Matter ecosystem and always-home controller, the exact Thread border-router model and generation, and the phone or app used for commissioning. For a Wi-Fi Matter device, replace the border-router check with Wi-Fi band, LAN, and account requirements.