feat(python): add model_dump_json override to handle FieldMetadata aliases

generators/python/core_utilities/shared/pydantic_utilities.py

@@ -91,6 +91,20 @@ def json(self, **kwargs: Any) -> str:
             return super().model_dump_json(**kwargs_with_defaults)  # type: ignore[misc]
         return super().json(**kwargs_with_defaults)
 
+    def model_dump_json(self, **kwargs: Any) -> str:
+        """
+        Override model_dump_json to use our custom dict() method which properly
+        handles FieldMetadata aliases, then serialize to JSON.
+        """
+        import json
+
+        data = self.dict(**kwargs)
+        if IS_PYDANTIC_V2:
+            from pydantic_core import to_jsonable_python
+
+            return json.dumps(to_jsonable_python(data, fallback=encode_by_type))
+        return json.dumps(data, default=encode_by_type)
+
     def dict(self, **kwargs: Any) -> Dict[str, Any]:
         """
         Override the default dict method to `exclude_unset` by default. This function patches

generators/python/core_utilities/shared/with_pydantic_v1_on_v2/pydantic_utilities.py

@@ -54,6 +54,16 @@ def json(self, **kwargs: Any) -> str:
         }
         return super().json(**kwargs_with_defaults)
 
+    def model_dump_json(self, **kwargs: Any) -> str:
+        """
+        Override model_dump_json to use our custom dict() method which properly
+        handles FieldMetadata aliases, then serialize to JSON.
+        """
+        import json
+
+        data = self.dict(**kwargs)
+        return json.dumps(data, default=encode_by_type)
+
     def dict(self, **kwargs: Any) -> Dict[str, Any]:
         """
         Override the default dict method to `exclude_unset` by default. This function patches

generators/python/sdk/versions.yml

@@ -1,5 +1,15 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
 # For unreleased changes, use unreleased.yml
+- version: 4.43.0
+  changelogEntry:
+    - summary: |
+        Add `model_dump_json()` override to `UniversalBaseModel` that properly handles `FieldMetadata` aliases.
+        When using the default `FieldMetadata` aliasing (not native Pydantic aliases), calling `model_dump_json()`
+        now correctly serializes field names to their camelCase aliases, matching the behavior of `dict()`.
+      type: feat
+  createdAt: "2025-12-05"
+  irVersion: 61
+
 - version: 4.42.0
   changelogEntry:
     - summary: |