Cryptomatte in the Arnold User Guide for the full shader documentation.
Arnold supports cryptomatte, an ID matte creation tool created by Jonah Friedman. It creates ID mattes automatically with support for motion blur, transparency, and depth of field.
Cryptomatte shader available in Shop> Arnold Vopnet
Create an OUT_AOV node and connect your Cryptomatte node to it.
Connect a cryptomatte shader to AOV shaders in the Arnold ROP (Properties > Output tab).
Render the Cryptomatte AOVs to disk (as EXR).
Opening the EXR in a compositing package such as Nuke or Fusion shows the available cryptomatte AOVs.
Note:
There is a limitation with the current cryptomatte implementation, where object names are expected to follow the MtoA naming convention. A workaround is to manually set the " crypto_asset " string attribute on the geometry you want to belong to the same asset ID, which works.
