(update to this post will be at the bottom of the post unless stated otherwise. also old update will be moved to the comments because of the character cap of 4000. Got my k1 cfs upgrade kit today. just finished installing it on my k1 max I have got it working fine so far with the original hot end installed all I had to do was cut a PTFE tube to the right length and increased the opening at the extruder end. I have the unicorn upgrade on the way but it can work with the old extruder with very little work and so far it's been consistent. only issue I had was me trying to use the cfs to feed the filament through about 2 metres worth of PTFE tube didn't work because it wouldn't retract. also I left the old filament sensor in for if I wanted to go back to the old extruder which I probably want do if the new extruder is consistent with the old hot end it means I can keep using my old nozzle. currently printing a 2 tone benchy in blue and white. I plan to do more testing to make sure the old extruder is long term viable. reply to the post and ask if you want to know how the long term viable of the old extruder run with the k1 cfs upgrade is going. (update as of the 5/6/2025) I have swapped from the original hotend and heatsink to the unicorn hotend. I didn't swap because I ran in to any big issue, I just wanted to try it and it was an special. I do plan to go back to the original hot end and continue this test but in the 1 to 2 mouth I had it run with the original hotend (no unicorn hotend) in it I hadn't run in to any feeding issue of filaments or cfs issue the only issue I had is what I stated in the comments of this post about the swaping to a different filament if the filament runs out does always work which I disable in the cfs to stop the issue. the issue I've had with the printer related to the cfs are most that you can assign colour in the creality cloud app which slicing a print which means you can use the cfs at all with out doing some Jake button masking which can lead to the second issue I found Is that the printer can start a print remotely or on the printer while it still trying to swap the filament when it in the little filament swap location, which is were it will get stuck because it goes to home the printer or just start the print and will eventually lead to you have your print head wedge in the filament swap location because the bed raised and got stuck of the filament swap pop scope thing. the final issue I have found and don't think I've seen any talk about this but you can't use the LIDAR on any of the k1 after the cfs upgrade I even got confirmation from creality support about that which took about a month and a half for me to get that answers from them from the repeat back and forth emails. also there are aprently trying or going to fix that creality cloud issue I mentioned earlier. so if you find any more that I haven't mentioned pls comments them down below I will see if I can help with is. also side note my k1 max might not have been running the original hotend recently but I have a close friend who I have installed a k1 cfs upgrade on his printer for him and his is also running the original hotend.)