diff --git a/litellm/types/llms/anthropic.py b/litellm/types/llms/anthropic.py
index ecb8dbb2502..bcdee86360e 100644
--- a/litellm/types/llms/anthropic.py
+++ b/litellm/types/llms/anthropic.py
@@ -586,7 +586,7 @@ class MessageBlockDelta(TypedDict):
 
     type: Literal["message_delta"]
     delta: MessageDelta
-    usage: NotRequired[UsageDelta]
+    usage: NotRequired[ReadOnly[UsageDelta]]
     context_management: NotRequired[ContextManagementResponse]
 
 
diff --git a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_handler.py b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_handler.py
index ac05cdcf251..32c98a83948 100644
--- a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_handler.py
+++ b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_handler.py
@@ -580,10 +580,9 @@ def test_text_only_streaming_has_index_zero():
 
 
 def test_message_delta_without_usage_returns_chunk_with_no_usage():
-    """A message_delta event may carry no usage field; it must not raise."""
-    iterator = ModelResponseIterator(None, sync_stream=True)
+    iterator: Final = ModelResponseIterator(None, sync_stream=True)
 
-    model_response = iterator.chunk_parser(
+    model_response: Final = iterator.chunk_parser(
         {
             "type": "message_delta",
             "delta": {"stop_reason": "end_turn", "stop_sequence": None},