IAB Feature (Integrated Access and Backhaul) in 5G

Is anyone aware of a 5G network that uses IAB feature integrated access and backhaul?

Its (IAB) part of Rel 16 work group, unsure it available today on commercial networks.

Whats is IAB? Access Barring of some sort?

Integrated Access Backhaul.
It replaces fiber to some 5G sites.
Transmission between sites is done on radio using PRBs. So if you have 20 5G sites with LOS to each other you need fiber just for 6-7 and rest will be connected via IAB feature.

Wow. Will it work like a side link i.e. on different band and frequency?

More details about IAB feature here: