Verdict
K1C is the K1 with a hardened steel nozzle stock + AI camera + slightly improved firmware. Same chassis, same Klipper, same 220mm cube.
Buy the K1C if: you'll print PETG-CF / PA-CF / glass-filled materials within 6 months. Hardened nozzle alone costs $25 and you'd add the camera for $50 anyway — so $100 premium is fair.
Buy the K1 if: mostly PLA / PETG / TPU, no plans for carbon-fiber-loaded filaments. Don't pay for what you won't use.