diff --git a/src/anthropic/lib/_parse/_transform.py b/src/anthropic/lib/_parse/_transform.py
index ce0c83ac..982e8375 100644
--- a/src/anthropic/lib/_parse/_transform.py
+++ b/src/anthropic/lib/_parse/_transform.py
@@ -107,11 +107,11 @@ def transform_schema(
         strict_schema["anyOf"] = [transform_schema(cast("dict[str, Any]", variant)) for variant in one_of]
     elif is_list(all_of):
         strict_schema["allOf"] = [transform_schema(cast("dict[str, Any]", variant)) for variant in all_of]
-    else:
-        if type_ is None:
-            raise ValueError("Schema must have a 'type', 'anyOf', 'oneOf', or 'allOf' field.")
-
+    elif type_ is not None:
         strict_schema["type"] = type_
+    # else: a typeless schema with no combinators — e.g. an empty `{}`, which pydantic
+    # emits for an `Any`-typed field or the items of an untyped `list`/`List[Any]`. This
+    # is a valid, unconstrained ("any") schema, so leave it untyped rather than raising.
 
     enum = json_schema.pop("enum", None)
     if is_list(enum):
diff --git a/tests/lib/_parse/test_transform.py b/tests/lib/_parse/test_transform.py
index 7a2799dc..e6ad00d7 100644
--- a/tests/lib/_parse/test_transform.py
+++ b/tests/lib/_parse/test_transform.py
@@ -1,6 +1,8 @@
 from copy import deepcopy
+from typing import Any, List
 
 import pytest
+import pydantic
 from inline_snapshot import snapshot
 
 from anthropic.lib._parse._transform import transform_schema
@@ -145,6 +147,57 @@ def test_array_schema():
     )
 
 
+def test_empty_schema():
+    # pydantic emits a bare `{}` for an `Any`-typed field; an empty schema is a
+    # valid, unconstrained ("any") schema and must not raise.
+    assert transform_schema({}) == snapshot({})
+
+
+def test_array_with_untyped_items():
+    # `list` / `List[Any]` produces `{"type": "array", "items": {}}`.
+    schema: dict[str, Any] = {"type": "array", "items": {}}
+    result = transform_schema(schema)
+    assert result == snapshot({"type": "array", "items": {}})
+
+
+def test_object_with_any_property():
+    schema: dict[str, Any] = {"type": "object", "properties": {"x": {}}, "required": ["x"], "title": "M"}
+    result = transform_schema(schema)
+    assert result == snapshot(
+        {
+            "type": "object",
+            "title": "M",
+            "properties": {"x": {}},
+            "additionalProperties": False,
+            "required": ["x"],
+        }
+    )
+
+
+def test_model_with_untyped_list_and_any_field():
+    # Regression: previously raised ValueError("Schema must have a 'type', ...") because
+    # the untyped `list` items / `Any` field transform to an empty `{}` sub-schema.
+    class Result(pydantic.BaseModel):
+        summary: str
+        tags: List[Any]
+        extra: Any
+
+    result = transform_schema(Result)
+    assert result == snapshot(
+        {
+            "type": "object",
+            "title": "Result",
+            "properties": {
+                "summary": {"type": "string", "title": "Summary"},
+                "tags": {"type": "array", "title": "Tags", "items": {}},
+                "extra": {"title": "Extra"},
+            },
+            "additionalProperties": False,
+            "required": ["summary", "tags", "extra"],
+        }
+    )
+
+
 def test_string_schema_with_format_and_default():
     schema = {
         "type": "string",