The idea of thread is that it is basically IPv6 over Zigbee, in the form of 6LoWPAN which is an IPv6 stack optimized for low-power devices with an addressing, discovery, and routing mechanism designed to work well on mesh networks like Zigbee.
To some extent, Thread and Matter are direct replacements for Z-wave at different levels of the stack. There are some different pros/cons between the two though. The major advantage of 6LoWPAN is that it shares a lot of the design and implementation with existing network stacks and can be carried directly over IP networks. This is expected to make more complex 6LoWPAN topologies much easier to implement (e.g. 6LoWPAN traffic can be easily forwarded over the internet by a gateway). None of this is really anything that can't be done with Z-wave, but 6LoWPAN makes it easier by having a lot of common design and implementation with ubiquitous IP stacks. Matter itself has the major advantage of being a newer and higher-level design than Z-Wave which should result in more consistent interoperability of a wider range of devices.
Z-wave will probably remain superior for battery-powered sensors into the future, because Thread doesn't allow for the extremely aggressive sleep schedules (e.g. sleep mode for 18 hours at a time between supervisions for security sensors) that Z-Wave does... although we can of course debate how wise it is to only perform supervision every 18 hours, even if UL allows it for burglar alarms.
I believe would be more accurate to say it's Zigbee over IPv6.
IIRC Zigbee is: 802.15.4 -> "Zigbee"
And my (mostly incomplete) understanding of matter is it's: 802.15.4 -> 6LoWPAN -> Thread -> "The device model of Zigbee"-like Application Layer (for thread devices)
I'm using the terminology in a confusing way. Thread and Zigbee are both protocols on top of 802.15.4, but to be fair to myself there is a really common tendency to refer to "bare" 802.15.4 as Zigbee mostly because of the history. Zigbee is a very "thin" protocol though compared to Thread which is a lot more ambitious, but at the same time Zigbee goes more into application space... which kind of makes the point that Thread and Matter are a lot more "detailed" than Zigbee, which is minimalistic to the degree that interoperability of Zigbee products has always been very poor. This is one of the major reasons that Z-Wave mostly replaced Zigbee in the "smart home" space. It standardizes more functionality that Zigbee does. Thread and particularly Matter, in turn, standardize even more than Z-Wave (e.g. many of the things that are Z-wave config "mystery registers" that vary between manufacturers are included in Matter specs).
> This is one of the major reasons that Z-Wave mostly replaced Zigbee in the "smart home" space.
It did? I moved into a new home a year ago and have been outfitting it with smart devices. I have no real preference for Zigbee but ended up with a bunch of Zigbee devices and zero Z-Wave devices.
Me too, after getting two battery powered Wi-Fi enabled devices which are rather inconvenient. Z-Wave is somewhat better if you have a big house or many neighbours with 2.4 GHz Wi-Fi APs using the spectrum because it operates on the 868/908 MHz ISM band instead of the 2.4 GHz ISM band used by Zigbee and shared with Wi-Fi and BT devices. Lower frequency waves travel more easily through thick walls and further and the 868/908 band is also subject to airtime restrictions in order to prevent interference. ZigBee uses repeaters and more frequent updates to accomplish the same thing. Most wall plug powered ZigBee devices are also repeaters. You'll probably get more samples from battery powered ZigBee sensors than from devices either using Z-Wave (which has airtime limitations) or Wi-Fi (which is power hungry and the devices are in deep sleep most of the time).
To some extent, Thread and Matter are direct replacements for Z-wave at different levels of the stack. There are some different pros/cons between the two though. The major advantage of 6LoWPAN is that it shares a lot of the design and implementation with existing network stacks and can be carried directly over IP networks. This is expected to make more complex 6LoWPAN topologies much easier to implement (e.g. 6LoWPAN traffic can be easily forwarded over the internet by a gateway). None of this is really anything that can't be done with Z-wave, but 6LoWPAN makes it easier by having a lot of common design and implementation with ubiquitous IP stacks. Matter itself has the major advantage of being a newer and higher-level design than Z-Wave which should result in more consistent interoperability of a wider range of devices.
Z-wave will probably remain superior for battery-powered sensors into the future, because Thread doesn't allow for the extremely aggressive sleep schedules (e.g. sleep mode for 18 hours at a time between supervisions for security sensors) that Z-Wave does... although we can of course debate how wise it is to only perform supervision every 18 hours, even if UL allows it for burglar alarms.