diff --git a/zeromodels/base/base_config.py b/zeromodels/base/base_config.py
index efbb9437..c3d66579 100644
--- a/zeromodels/base/base_config.py
+++ b/zeromodels/base/base_config.py
@@ -78,14 +78,45 @@ def field_names(cls):
     def unknown_keys(cls, data):
         """Keys in a repo spec ``data`` this config does not recognize.
 
-        A typed config's ``from_dict`` keeps only annotated fields, so a key a newer
-        zeromodels added (e.g. ``rope_scaling_factor``, nested under ``text_config``)
-        is dropped. This finds those by round-trip: a key present in ``data`` but
-        absent from ``to_dict(from_dict(data))`` was not consumed. It recurses into
-        the nested sub-config dicts the repo format wraps fields in, and never flags
-        a legitimate key (a recognized key always round-trips back).
+        Match the input routes used by ``from_dict``, not its serialized output:
+        serialization relocates flat fields and omits absent optional towers and
+        some glue fields. Only declared config blocks are traversed; dictionary
+        values of ordinary fields (e.g. ``rope_scaling``) are opaque here. This
+        checks field names, not value types.
         """
-        known = cls.from_dict(data).to_dict()
+
+        def constructor_schema(config_cls):
+            schema = dict.fromkeys(config_cls.field_names())
+            for key, sub_cls in config_cls.sub_configs.items():
+                schema[key] = constructor_schema(sub_cls)
+            return schema
+
+        known = dict.fromkeys(cls.field_names())
+        if cls.sub_configs:
+            if any(key in data for key in cls.sub_configs):
+                known = constructor_schema(cls)
+            else:
+                for key, sub_cls in cls.sub_configs.items():
+                    for field in sub_cls.field_names():
+                        known[cls._sub_flat_name(key, field)] = None
+        else:
+            main_key = cls._main_key()
+            if main_key in data or "text_config" in data or "vision_config" in data:
+                fields = set(cls.field_names())
+                if main_key not in cls.config_groups:
+                    known[main_key] = dict.fromkeys(fields)
+                for key, prefix in cls.config_groups.items():
+                    extras = set(cls.group_extras.get(key, ()))
+                    members = {
+                        field[len(prefix) :]
+                        for field in fields
+                        if field.startswith(prefix)
+                        and field[len(prefix) :] not in extras
+                    }
+                    members.update(extras & fields)
+                    known[key] = dict.fromkeys(members)
+        if cls.model_type is not None:
+            known["model_type"] = None
 
         def diff(spec, seen):
             out = set()
diff --git a/zeromodels/models/sam2/sam2_layers.py b/zeromodels/models/sam2/sam2_layers.py
index a4735f51..d798310b 100644
--- a/zeromodels/models/sam2/sam2_layers.py
+++ b/zeromodels/models/sam2/sam2_layers.py
@@ -1590,7 +1590,9 @@ def _recompute_full_pos(self):
         dtype = "float64" if self.pos_embed.dtype == "float64" else "float32"
         matrices = []
         for out_size, in_size in ((h, self.bg_size[0]), (w, self.bg_size[1])):
-            center = (ops.arange(out_size, dtype=dtype) + 0.5) * (in_size / out_size) - 0.5
+            center = (ops.arange(out_size, dtype=dtype) + 0.5) * (
+                in_size / out_size
+            ) - 0.5
             start = ops.floor(center)
             fraction = center - start
             a = -0.75
@@ -1605,14 +1607,18 @@ def _recompute_full_pos(self):
             for offset, tap in zip((-1, 0, 1, 2), taps):
                 index = ops.clip(ops.cast(start, "int32") + offset, 0, in_size - 1)
                 # Accumulate duplicate taps when border indices are clamped.
-                matrix = matrix + ops.one_hot(index, in_size, dtype=dtype) * tap[:, None]
+                matrix = (
+                    matrix + ops.one_hot(index, in_size, dtype=dtype) * tap[:, None]
+                )
             matrices.append(matrix)
         pos = ops.cast(self.pos_embed, dtype)
         pos = ops.einsum("wj,bijc->biwc", matrices[1], pos)
         pos = ops.einsum("hi,biwc->bhwc", matrices[0], pos)
         tile_h = h // self.window_size
         tile_w = w // self.window_size
-        window_pos = ops.tile(ops.cast(self.pos_embed_window, dtype), (1, tile_h, tile_w, 1))
+        window_pos = ops.tile(
+            ops.cast(self.pos_embed_window, dtype), (1, tile_h, tile_w, 1)
+        )
         self._full_pos.assign(pos + window_pos)
 
     def load_own_variables(self, store):