This is a seemingly simple question. But I can't find an answer. Suppose I have a smart switch or light bulb, or similar Matter/Thread IoT device in my home. Can that device talk to the internet?
Let's start with what I think I know:
The Thread standard is based on IPv6. Thread devices behave like all IPv6 devices. Each device obtains a link local address. Plus maybe other addresses via SLAAC or DHCPv6.
A Thread Border Router, if present, will assign additional IPv6 addresses. These might be ULAs (Unique Local Address) or GUAs (Global Unicast Address). That is a function of the Thread Border Router and what features it offers. If the Thread Border Router provides a GUA, the device has internet connectivity over IPv6.
A Thread Border Router may also provide NAT64, giving Thread devices access to talk to the public internet over IPv4.
This is what the standard allows. But what is the reality with today's consumer devices? Suppose I install a latest gen AppleTV or HomePod in my home LAN. Both devices act as Thread Border Routers. In order to allow my smart switch or light bulb to talk to the internet, the AppleTV/HomePod would have to:
Support DHCPv6-PD as a client to obtain an IPv6 global /64 prefix to assign to the Thread network. Very few if any home routers will support DHCPv6-PD. I very much doubt Apple is supporting this.
Support manual configuration of an IPv6 global prefix for the Thread network. It's Apple. They don't offer this.
Conclusion: Any Matter/Thread device behind an AppleTV or HomePod has no internet connectivity over IPv6.
Now, what about IPv4? The Thread standard allows a Thread Border Router to offer NAT64. That allows devices on the IPv6 Thread network, to talk to IPv4 devices on the public internet. Does the AppleTV/HomePod offer NAT64? I do not know and I don't know how to test it.
The question, again: If I have a Thread Border Router such as an AppleTV or HomePod, can my light bulbs or smart switches make an outgoing IP connection to the public internet?