diff --git a/unsloth/models/loader.py b/unsloth/models/loader.py
index 459b6ed32d..09dd5364d4 100644
--- a/unsloth/models/loader.py
+++ b/unsloth/models/loader.py
@@ -1234,7 +1234,14 @@ class FastModel(FastBaseModel):
 
         # Save model types and loading method
         lowered_model_name = model_name.lower()
-        string = os.environ.get("UNSLOTH_MODEL_NAME", "") + model_types_all
+        # Build UNSLOTH_MODEL_NAME freshly from THIS load's model name + flags. Do not
+        # prepend the previous os.environ value: it persists in-process and is inherited
+        # across processes (e.g. a save->reload subprocess), so it accumulates stale load
+        # flags. A leftover "_load_in_4bit_" from an earlier bnb-4bit load would make
+        # gpt-oss wrongly take the BnB router patch (router.linear.weight) when later
+        # reloading a merged 16bit checkpoint (router.weight), raising
+        # "Unsloth: Critical error since some weights are not initialized".
+        string = lowered_model_name + "," + model_types_all
         if load_in_4bit:
             string += "_load_in_4bit_"
         if load_in_8bit: