Thread is a low-power IPv6 mesh protocol built on IEEE 802.15.4 (the same physical layer as Zigbee but a different upper stack), used by Matter for battery-powered devices such as sensors and locks where battery life ranges from several months to several years.

Thread shares the IEEE 802.15.4 physical layer at 2.4 GHz with Zigbee but stops there: its network layer is 6LoWPAN plus native IPv6, whereas Zigbee uses a proprietary networking stack. Thread is a true mesh in which router-capable nodes forward traffic for their neighbours, and a Thread Border Router bridges the 802.15.4 mesh to Wi-Fi or Ethernet at the IP layer. Sleepy End Devices implement aggressive sleep modes, which is why coin-cell sensors and battery locks reach multi-year autonomy. The protocol is maintained by the Thread Group, a sister consortium of the CSA.

Do not confuse the physical layer with the stack: Zigbee and Thread share the same chip family but a Zigbee device cannot join a Thread mesh and vice versa, only a bridge can ferry data between them.