The way I understand it (please correct me) is that:

* The old Ikea Zigbee products will remain Zigbee. They will still require a Zigbee coordinator.

* The new products will be Matter-over-Thread. They require a Thread coordinator (or whatever the Thread equivalent is called).

* The existing Ikea hub has had a firmware upgrade that allows it to be simultaneously a Zigbee and Thread coordinator.

* The Ikea hub adds a Matter compatibility layer to the devices that don't natively support Matter.