Thread is an IPv6-based, low-power mesh networking technology for Internet of things (IoT) products. It is built on the IEEE 802.15.4 radio standard and uses 6LoWPAN to carry IPv6 packets over low-power, low-bandwidth links. Often used as a transport for the home-automation connectivity standard Matter (the combination being known as Matter over Thread), the protocol has seen increased use for connecting low-power and battery-operated smart-home devices.

Because every Thread device is individually IP-addressable, application data can be routed to and from the wider network without an application-layer gateway; this distinguishes Thread from technologies such as Zigbee that share the same radio but are not natively IP-based. Thread defines only the networking layers and specifies no application layer of its own, leaving that role to standards such as Matter or to vendor-specific stacks.

Thread originated at Nest Labs, which began developing it around 2011 as a proprietary networking layer for its own connected-home products before the technology was opened to the wider industry. Since July 2014 the protocol has been developed and maintained by the Thread Group, a not-for-profit industry alliance formed to develop, maintain and drive adoption of Thread as an industry networking standard for IoT applications. The Thread Group also certifies components and finished products for conformance and interoperability. The Thread specification is published at no cost but its use is governed by an end-user license agreement, and building or shipping Thread products requires Thread Group membership.

History

Origins at Nest (2011–2014)

Thread began as an in-house effort at Nest Labs. The company started developing the protocol around 2011 to give its own connected-home products a common, reliable, low-power networking layer, and it built the technology into its devices from the outset—beginning with the first Nest Learning Thermostat. At Nest, Thread served as the network layer beneath the company's own application layer, Weave; because Thread itself defines no application layer, an application protocol such as Weave (or, later, Zigbee's Cluster Library or Matter) is required to make devices interoperate.

In January 2014, Google acquired Nest Labs for US$3.2 billion, with Nest continuing to operate under its own brand. About six months later, Nest worked with ARM, Samsung and other companies to propose Thread as an open industry standard rather than a Nest-only technology.

Thread Group and standardization (2014–2018)

In July 2014, the Thread Group alliance was formed to develop, maintain and drive adoption of Thread as an industry networking standard for IoT applications, and it opened membership in October 2014. Initial members were ARM Holdings, Big Ass Solutions, NXP Semiconductors/Freescale, Nest Labs, OSRAM, Samsung, Silicon Labs, Somfy, Tyco International, Qualcomm, and the Yale lock company. In its early years the Thread Group was led by Nest employees; Chris Boross served as its first president, and Nest principal engineer Grant Erickson succeeded him in 2016.

In April 2015 the Thread Group and the Zigbee Alliance announced a collaboration to allow the Zigbee Cluster Library application layer to run over Thread networks. The first public Thread specification was released on 13 July 2015.

In May 2016, Nest released OpenThread, an open-source reference implementation of Thread, on GitHub under a three-clause BSD license, allowing anyone to reuse, modify or redistribute it. The move was intended to accelerate adoption: because Thread is an IPv6 protocol built on open standards, many existing 802.15.4 devices could be updated to run it, and manufacturers could adopt a common stack rather than write their own. Companies contributing to OpenThread's development included ARM, Atmel (a subsidiary of Microchip Technology), Dialog Semiconductor, Qualcomm Technologies and Texas Instruments, and it ran on Thread-compatible radios from silicon vendors such as NXP and Silicon Labs. OpenThread has since been maintained by Google, which absorbed Nest's platform teams.

The Thread Group launched its formal certification program in 2017. In August 2018, Apple joined the group, and released its first Thread product, the HomePod Mini, in late 2020.

Matter and recent developments (2019–present)

In 2019, the Connected Home over IP (CHIP) project—subsequently renamed Matter—led by the Zigbee Alliance, now the Connectivity Standards Alliance (CSA), Google, Amazon and Apple, announced a broad collaboration to create a royalty-free standard and open-source code base to promote interoperability in home connectivity, leveraging Thread, Wi-Fi and Bluetooth Low Energy. Amazon joined the Thread Group board of directors in November 2021.

Thread 1.3 was released in 2022 alongside Matter 1.0, aligning Thread as Matter's low-power mesh transport. Thread 1.4 followed in September 2024, extending the protocol toward larger commercial and industrial deployments. In November 2025 the Thread Group reported that more than 1,000 Thread-certified products had reached the market—roughly a tenfold increase in two years—and that it had more than 230 member companies. From 1 January 2026, new Thread border routers can be certified only against Thread 1.4; Thread 1.3 applications are no longer accepted. In March 2026, Schneider Electric joined the Thread Group board of directors.

Technical specification Thread occupies the networking layers of the OSI model and assembles several established IEEE and IETF standards into a low-power IP stack; it does not define an application layer.

Protocol stack + Thread protocol stack Layer Technology and role Application Not defined by Thread. Any IPv6-capable application layer—Matter, DALI+, CoAP-based or proprietary—runs on top, and more than one can share a single network. Transport UDP for mesh maintenance and most traffic; a TCP profile added in Thread 1.3; the Constrained Application Protocol (CoAP) layered on UDP for request/response and retries; DTLS for secured commissioning. Network IPv6 with distance-vector mesh routing and Mesh Link Establishment (MLE) for neighbour and route maintenance. Adaptation 6LoWPAN, which fragments and reassembles IPv6 packets to fit small 802.15.4 frames and compresses headers. PHY / MAC IEEE 802.15.4 (2006 and 2015 editions): 250 kbit/s in the 2.4 GHz band using DSSS and O-QPSK modulation, CSMA/CA channel access, 127-byte frames, link-layer acknowledgements, retries and AES.

Radio and physical layer Thread operates in the 2.4 GHz ISM band across 802.15.4 channels 11–26, transmitting at 250 kbit/s with direct-sequence spread spectrum and offset-QPSK modulation. Typical range is about per hop indoors; the mesh extends effective coverage beyond a single link, and channel agility (introduced in Thread 1.1) lets a network move channels to avoid interference. Because the band is shared with Wi-Fi, deployments often favour the 802.15.4 channels that fall between common Wi-Fi channels (such as 15, 20, 25 and 26) to reduce contention.

Above these layers the specification also defines management and service components—including the Mesh Commissioning Protocol (MeshCoP), a Thread Management Framework built on CoAP, Multicast Protocol for Low-power and Lossy Networks (MPL) for network-wide multicast, and Thread diagnostics—that handle commissioning, configuration distribution and network monitoring.

Device types and roles

Thread defines two hardware classes—the Full Thread Device (FTD) and the constrained Minimal Thread Device (MTD)—and a set of roles that the network assigns and reassigns automatically.

+ Thread device roles Role Class Function Leader FTD A single elected router that makes network-wide decisions, such as assigning router IDs. The role is re-elected automatically if the leader fails. Router FTD Forwards packets and provides joining and security services; remains powered on. Router-Eligible End Device (REED) FTD Can be promoted to a router by the leader when the topology requires it, without user action. Full End Device (FED) FTD Retains full function but never becomes a router. Minimal End Device (MED) MTD Communicates only through a parent router; keeps its radio on when idle. Sleepy End Device (SED) MTD Keeps its radio off while idle, waking periodically to poll its parent, enabling multi-year battery life. Synchronized Sleepy End Device (SSED) MTD Wakes on a scheduled interval (coordinated sampled listening) to listen for its parent. Border Router FTD Bridges the Thread mesh to adjacent IP networks such as Wi-Fi or Ethernet (see below).

Topology, mesh and routing

A Thread network with more than one router forms a mesh; a single-router network is a star. The number of active routers is managed adaptively by the protocol—typically 16 to 32 in a larger network—up to a hard limit of 32 active router IDs. Each router can parent a large number of end devices (the specification allows up to 511 children per router, subject to the parent's memory), so that although a subnet is generally recommended to hold around 250 devices, the specification's theoretical ceiling is roughly 16,000 devices. Routers exchange compact MLE advertisements using a distance-vector routing scheme conceptually similar to RIPng. Each router advertises, in a single byte per neighbouring router, its incoming and outgoing link quality (two bits each) and the routing cost (four bits)—link quality being derived from the received signal margin—so that every router continuously maintains least-cost paths to every other router.

The network is designed with no single point of failure: it self-configures, self-optimizes and self-heals. If a router drops out, traffic is re-routed; if the leader fails, another router is elected; and if a sleepy device loses its parent, it re-attaches to a new one—all without user intervention. Thread also runs locally: within the home, phones and other controllers can address devices directly through a border router rather than relaying commands through the cloud, which reduces latency.

Addressing

On joining a network, each Thread device configures at least three unicast IPv6 addresses on its interface: a link-local address (LL64, prefix fe80::/10), valid only between direct radio neighbours and used mainly for link establishment; a Mesh-Local EID (ML-EID, ML64), a topology-independent address with a random interface identifier that remains stable as the mesh changes and is used to reach a device anywhere in the network; and a Routing Locator (RLOC, ML16), a topology-dependent address whose 16-bit interface identifier encodes the device's router ID and child position. The mesh-local addresses share a per-network Unique Local prefix (fd followed by five bytes of the network's extended PAN ID). Devices also join "all Thread nodes" multicast groups at link-local and realm-local scope, and border routers can advertise additional global or unique-local prefixes that devices configure through SLAAC or DHCPv6.

Security and commissioning