Early Opteron (with Socket 940) topped at 8 sockets glueless - with the same chipset one could drive a socket 754 chip.
However, with custom glue logic, one could expand it very far - AMD offering in that space was "Horus" chipset which connected 4 sockets with external fabric (infiniband, iirc) to create 64 socket systems. Similar tactic was (and still is) offered by SGI in their UltraViolet systems which utilize the same principle using NUMAlink fabric and Xeon cpus.
However, with custom glue logic, one could expand it very far - AMD offering in that space was "Horus" chipset which connected 4 sockets with external fabric (infiniband, iirc) to create 64 socket systems. Similar tactic was (and still is) offered by SGI in their UltraViolet systems which utilize the same principle using NUMAlink fabric and Xeon cpus.