--load-filament-ids

Assigns a filament slot to each input model file, in order. The value is a comma-separated list of 1-based slot integers -- one integer per input file. The slicer reads the list positionally: the first integer maps to the first input file, the second integer to the second input file, and so on. When a slot number greater than zero is provided for a file, the slicer writes that value to every object loaded from that file as its extruder config key, binding it to that filament slot during slicing.

A slot value of 0 is treated as "no assignment": the slicer leaves the extruder config on those objects untouched, which in practice means the object inherits whatever default the slicing profile provides. Non-zero values must not exceed the number of slots declared via --load-filaments; any value that does is a fatal error that aborts with CLI_INVALID_PARAMS. Because the assignment is set on the whole object, it applies uniformly to every mesh the file contains -- there is no per-volume override through this flag.

This flag is only meaningful when input files are non-3MF geometry (STL, OBJ, or similar). If the first input file is a .3mf, the slicer rejects the flag outright with a fatal error, because a 3MF already embeds its own extruder assignments and slot configuration inside the archive. The flag also unconditionally requires --load-filaments to be present; omitting --load-filaments while supplying --load-filament-ids is itself a fatal error, regardless of how many slots the project file might otherwise define.