@Ryan R in general if you have the extracted netlist of a circuit block, simply declare the type of the symbol in your testbench to be '`primitive`' instead of '`subcircuit`'. Xschem will not generate the .subckt // .ends section of the symbol. You have to manually add something like

.include /path/to/extracted_netlist.spice

to use the extracted netlist for the block. You must ensure the port order of the extracted subcircuit netlist and the xschem generated subcircuit match. See also this video about using different descriptions for a symbol. It covers verilog but all concepts are valid for spice sims as well.

I have a follow up question @Stefan Schippers — if I have a magic-extracted netlist that I include within the netlist symbol’s value as .include /path/to/spice, can I directly instance the model/subcircuit from the spice file within the netlist value? Something like

include /path/to/extracted/.spice

x1 [ports] subcircuit-name-from-spice

Or would a symbol be necessary? I am able to get a netlist to generate with the include and instance definition method but I am messing something up as ngspice doesn’t want to quite run it…