diff --git a/coreml_suite/nodes.py b/coreml_suite/nodes.py
index 776a346..96f1d78 100644
--- a/coreml_suite/nodes.py
+++ b/coreml_suite/nodes.py
@@ -247,12 +247,15 @@ class CoreMLConverter(COREML_NODE):
                     ],
                 ),
                 "controlnet_support": ("BOOLEAN", {"default": False}),
-                # Phase 6: k-means weight palettization. "none" keeps the
-                # pre-Phase-6 behavior and filename, so existing cached
-                # .mlpackages still resolve.
-                "quantize_nbits": (list(QUANT_NBITS_VALUES), {"default": "none"}),
             },
             "optional": {
+                # Phase 6: k-means weight palettization. Kept optional so
+                # workflows saved before Phase 6 still validate — ComfyUI
+                # rejects a prompt that omits any `required` input. When
+                # omitted it defaults to "none", identical to pre-Phase-6
+                # behavior and filename, so existing cached .mlpackages
+                # still resolve.
+                "quantize_nbits": (list(QUANT_NBITS_VALUES), {"default": "none"}),
                 "lora_params": ("LORA_PARAMS",),
             },
         }