Network architecture of AlphaZero
The AlphaGo Zero paper tests a few different architectures:


Seperate 12-convolutional-block policy and value networks (as in AlphaGo)
A single 12-convolutional-block network with dual policy and value outputs
Separate 20-residual-block networks
A single 20-residual-block network with dual policy and value outputs
A single 40-residual-block network with dual policy and value outputs


In the AlphaZero paper AlphaZero Go wins 60 games in a 100-game match against the 20-block single resnet AlphaGo Zero, but it is not explicitly stated which architecture AlphaZero is using. It is either the 40-block single resnet since this was the best, or it is the 20-block single resnet in order to make a fair comparison with AlphaGo Zero.