diff --git a/litellm/litellm_core_utils/llm_response_utils/convert_dict_to_response.py b/litellm/litellm_core_utils/llm_response_utils/convert_dict_to_response.py
index f3c60679c81..9cad20a1420 100644
--- a/litellm/litellm_core_utils/llm_response_utils/convert_dict_to_response.py
+++ b/litellm/litellm_core_utils/llm_response_utils/convert_dict_to_response.py
@@ -800,6 +800,15 @@ def convert_to_model_response_object(
             if "usage" in response_object and response_object["usage"] is not None:
                 usage_object: Final = litellm.Usage(**response_object["usage"])
                 setattr(model_response_object, "usage", usage_object)
+            else:
+                # The provider sent no usage (missing or explicit null). The
+                # pre-attached empty Usage() keeps zero-filled counts as the
+                # default for downstream consumers, but a missing block would
+                # be indistinguishable from a real zero - record the absence
+                # so callers can tell the two apart.
+                cast(  # cast-ok: hidden_params is normalized to a dict in the function prelude
+                    dict[str, object], hidden_params
+                ).update({"usage_missing": True})
             if "created" in response_object:
                 model_response_object.created = safe_convert_created_field(response_object["created"])
 
diff --git a/tests/unit/litellm_core_utils/llm_response_utils/test_convert_dict_to_response.py b/tests/unit/litellm_core_utils/llm_response_utils/test_convert_dict_to_response.py
index 0c601a6b2c8..33544a338b6 100644
--- a/tests/unit/litellm_core_utils/llm_response_utils/test_convert_dict_to_response.py
+++ b/tests/unit/litellm_core_utils/llm_response_utils/test_convert_dict_to_response.py
@@ -2968,3 +2968,73 @@ def test_convert_to_model_response_object_function_output():
     assert result.usage.completion_tokens_details == CompletionTokensDetailsWrapper(reasoning_tokens=0)
 
     assert result._hidden_params is not None
+
+
+COMPLETION_RESPONSE_WITHOUT_USAGE = {
+    "id": "chatcmpl-no-usage",
+    "created": 1784657740,
+    "model": "gpt-5.6",
+    "object": "chat.completion",
+    "choices": [
+        {
+            "finish_reason": "stop",
+            "index": 0,
+            "message": {"role": "assistant", "content": "Hello"},
+        }
+    ],
+}
+
+COMPLETION_RESPONSE_NULL_USAGE = {**COMPLETION_RESPONSE_WITHOUT_USAGE, "usage": None}
+
+COMPLETION_RESPONSE_ZERO_USAGE = {
+    **COMPLETION_RESPONSE_WITHOUT_USAGE,
+    "usage": {"completion_tokens": 0, "prompt_tokens": 0, "total_tokens": 0},
+}
+
+
+def test_convert_to_model_response_object_marks_missing_usage():
+    # main.py's completion() pre-attaches an empty Usage() before the provider
+    # reply is parsed; without a marker, a missing block looks like a real 0.
+    model_response: Final = ModelResponse()
+    setattr(model_response, "usage", litellm.Usage())
+
+    result: Final = convert_to_model_response_object(
+        response_object=COMPLETION_RESPONSE_WITHOUT_USAGE,
+        model_response_object=model_response,
+        response_type="completion",
+    )
+
+    assert result.hidden_params["usage_missing"] is True
+    # the zero-filled default stays intact for downstream consumers
+    assert result.usage.prompt_tokens == 0
+    assert result.usage.completion_tokens == 0
+
+
+def test_convert_to_model_response_object_marks_null_usage():
+    model_response: Final = ModelResponse()
+    setattr(model_response, "usage", litellm.Usage())
+
+    result: Final = convert_to_model_response_object(
+        response_object=COMPLETION_RESPONSE_NULL_USAGE,
+        model_response_object=model_response,
+        response_type="completion",
+    )
+
+    assert result.hidden_params["usage_missing"] is True
+    assert result.usage.total_tokens == 0
+
+
+def test_convert_to_model_response_object_real_zero_usage_not_marked():
+    model_response: Final = ModelResponse()
+    setattr(model_response, "usage", litellm.Usage())
+
+    result: Final = convert_to_model_response_object(
+        response_object=COMPLETION_RESPONSE_ZERO_USAGE,
+        model_response_object=model_response,
+        response_type="completion",
+    )
+
+    assert "usage_missing" not in result.hidden_params
+    assert result.usage.prompt_tokens == 0
+    assert result.usage.completion_tokens == 0
+    assert result.usage.total_tokens == 0
diff --git a/tests/unit/test_main.py b/tests/unit/test_main.py
index 14cea8f0c2c..6860d2af211 100644
--- a/tests/unit/test_main.py
+++ b/tests/unit/test_main.py
@@ -8732,3 +8732,70 @@ async def test_atranscription_ignores_a_non_string_base_url_when_api_base_is_set
 
     assert route.called
     assert response.text == "four score"
+
+
+def test_completion_marks_usage_missing_when_provider_omits_usage():
+    # Regression test for #45586: a usage-less provider response must be
+    # distinguishable from a real 0-token one.
+    api_base: Final = "http://localhost:12347/v1"
+    response_body: Final = {
+        "id": "chatcmpl-missing-usage",
+        "created": 1784657740,
+        "model": "gpt-5.6",
+        "object": "chat.completion",
+        "choices": [
+            {
+                "finish_reason": "stop",
+                "index": 0,
+                "message": {"role": "assistant", "content": "Hello"},
+            }
+        ],
+    }
+    with respx.mock(assert_all_called=False) as router:
+        mock_route: Final = router.post(url__regex=rf"{api_base}/chat/completions.*").mock(
+            return_value=httpx.Response(status_code=200, json=response_body)
+        )
+        response: Final = litellm.completion(
+            model="openai/gpt-5.6",
+            messages=[{"role": "user", "content": "Hello"}],
+            api_base=api_base,
+            api_key="fake_openai_api_key",
+        )
+    assert mock_route.called
+    assert response.hidden_params["usage_missing"] is True
+    # the zero-filled default stays intact for downstream consumers
+    assert response.usage.prompt_tokens == 0
+    assert response.usage.completion_tokens == 0
+
+
+def test_completion_real_zero_usage_is_not_marked_missing():
+    api_base: Final = "http://localhost:12348/v1"
+    response_body: Final = {
+        "id": "chatcmpl-zero-usage",
+        "created": 1784657740,
+        "model": "gpt-5.6",
+        "object": "chat.completion",
+        "choices": [
+            {
+                "finish_reason": "stop",
+                "index": 0,
+                "message": {"role": "assistant", "content": ""},
+            }
+        ],
+        "usage": {"completion_tokens": 0, "prompt_tokens": 0, "total_tokens": 0},
+    }
+    with respx.mock(assert_all_called=False) as router:
+        mock_route: Final = router.post(url__regex=rf"{api_base}/chat/completions.*").mock(
+            return_value=httpx.Response(status_code=200, json=response_body)
+        )
+        response: Final = litellm.completion(
+            model="openai/gpt-5.6",
+            messages=[{"role": "user", "content": "Hello"}],
+            api_base=api_base,
+            api_key="fake_openai_api_key",
+        )
+    assert mock_route.called
+    assert "usage_missing" not in response.hidden_params
+    assert response.usage.prompt_tokens == 0
+    assert response.usage.completion_tokens == 0
+    assert response.usage.total_tokens == 0