“Thread is very much neither free nor open.”
Thread is built on IEEE 802.15.4, IPv6 and CoAP, and OpenThread is BSD licensed. The spec license still grants no right to implement it, and the cheapest Thread Group membership that does costs USD 7,500 a year. The FAQ threatens legal action against anyone who ships without paying. Apple, Google and Amazon sit in the group and sell Thread as the open smart home standard. Open, for a fee.