I’ve done a load of testing around this recently, and the new filament auto-switch feature introduced in the latest firmware update only appears to work for the first AMS. If you have two or more AMS units, then it won’t auto switch between two filaments in different units - so run out of white PLA in AMS1 and it wont auto switch to a new spool in AMS2.
It also wont switch between two filaments in AMS2 and I presume not in 3 or 4.
If there’s no identical filament setup match in AMS1, OR if filament runs out in AMS2-4, then the X1C will prompt to replace the empty spool and tap the “resume” option. It does generally handle runouts well, even without the auto switch though, so if you only have 1 AMS and want a 4 colour print, you can still start with low-quantity spools so long as you have a replacement spool ready to replace it with when empty.
I also wonder what happens if the AMS detects the empty spool while printing a multi colour item and theres a colour change needed, since the printer won’t have initially detected the runout, and the AMS won’t be able to retract. I presume the two will work together and acknowledge the runout situation, and maybe the printer will purge everything remaining in the PTFE before indicating that a spool change is needed - but I’ve not been able to test this situation.