diff --git a/advanced_alchemy/service/_async.py b/advanced_alchemy/service/_async.py
index fd6e13b0..5fcbf808 100644
--- a/advanced_alchemy/service/_async.py
+++ b/advanced_alchemy/service/_async.py
@@ -473,6 +473,10 @@ def filter_unset(attr: Any, value: Any) -> bool:  # noqa: ARG001
                 **asdict(data, filter=filter_unset),
             )
 
+        # Check if data is already an instance of the expected model type
+        if isinstance(data, self.model_type):
+            return cast("ModelT", data)
+
         # Fallback for objects with __dict__ (e.g., regular classes)
         if hasattr(data, "__dict__"):
             return model_from_dict(
diff --git a/advanced_alchemy/service/_sync.py b/advanced_alchemy/service/_sync.py
index 98456594..76e8467b 100644
--- a/advanced_alchemy/service/_sync.py
+++ b/advanced_alchemy/service/_sync.py
@@ -472,6 +472,10 @@ def filter_unset(attr: Any, value: Any) -> bool:  # noqa: ARG001
                 **asdict(data, filter=filter_unset),
             )
 
+        # Check if data is already an instance of the expected model type
+        if isinstance(data, self.model_type):
+            return cast("ModelT", data)
+
         # Fallback for objects with __dict__ (e.g., regular classes)
         if hasattr(data, "__dict__"):
             return model_from_dict(
diff --git a/tests/integration/test_repository.py b/tests/integration/test_repository.py
index d92d9504..addae5f9 100644
--- a/tests/integration/test_repository.py
+++ b/tests/integration/test_repository.py
@@ -339,7 +339,10 @@ async def test_repo_update_method(seeded_test_session_async: "tuple[AsyncSession
     # Get first author
     authors = await maybe_async(author_repo.list())
     author = authors[0]
+
     original_name = author.name
+    original_created_at = author.created_at
+    original_updated_at = author.updated_at
 
     # Update the author
     author.name = "Updated Name"
@@ -347,6 +350,8 @@ async def test_repo_update_method(seeded_test_session_async: "tuple[AsyncSession
 
     assert updated_author.name == "Updated Name"
     assert updated_author.name != original_name
+    assert updated_author.created_at == original_created_at
+    assert updated_author.updated_at > original_updated_at
 
 
 async def test_repo_update_many_method_stale_data_fix(
@@ -385,7 +390,7 @@ async def test_repo_update_many_method_stale_data_fix(
         # updated_at should be newer than before
         if updated_author.id == authors[0].id:
             assert updated_author.created_at == original_created_at
-            assert updated_author.updated_at >= original_updated_at
+            assert updated_author.updated_at > original_updated_at
 
 
 async def test_repo_update_many_mixed_types(seeded_test_session_async: "tuple[AsyncSession, dict[str, type]]") -> None:
@@ -498,11 +503,18 @@ async def test_service_update_method(seeded_test_session_async: "tuple[AsyncSess
     author = authors[0]
     author_id = author.id
 
+    original_name = author.name
+    original_created_at = author.created_at
+    original_updated_at = author.updated_at
+
     # Update via service - correct parameter order is (data, item_id)
-    update_data = {"name": "Service Updated Name"}
-    updated_author = await maybe_async(author_service.update(update_data, item_id=author_id))
+    author.name = "Service Updated Name"
+    updated_author = await maybe_async(author_service.update(author, item_id=author_id))
 
     assert updated_author.name == "Service Updated Name"
+    assert updated_author.name != original_name
+    assert updated_author.created_at == original_created_at
+    assert updated_author.updated_at > original_updated_at
 
 
 async def test_service_delete_method(seeded_test_session_async: "tuple[AsyncSession, dict[str, type]]") -> None:
@@ -679,6 +691,10 @@ async def test_service_update_many_schema_types_github_535(
 
     original_dob1 = author1.dob
     original_dob2 = author2.dob
+    original_created_at1 = author1.created_at
+    original_created_at2 = author2.created_at
+    original_updated_at1 = author1.updated_at
+    original_updated_at2 = author2.updated_at
 
     # Get ID type from model for dynamic schema creation
     # For Pydantic compatibility, we need to map database-specific types to Python types
@@ -720,9 +736,13 @@ class AuthorUpdateMsgspecSchema(msgspec.Struct):  # type: ignore[name-defined,mi
     # Verify: names were updated, but dobs remain unchanged
     assert updated_author1.name == "Updated Author One"
     assert updated_author1.dob == original_dob1  # Should be unchanged
+    assert updated_author1.created_at == original_created_at1
+    assert updated_author1.updated_at > original_updated_at1
 
     assert updated_author2.name == "Updated Author Two"
     assert updated_author2.dob == original_dob2  # Should be unchanged
+    assert updated_author2.created_at == original_created_at2
+    assert updated_author2.updated_at > original_updated_at2
 
 
 async def test_repo_update_many_non_returning_backend_refresh(