diff --git a/litellm/main.py b/litellm/main.py
index 04b0963851a..ced63391fca 100644
--- a/litellm/main.py
+++ b/litellm/main.py
@@ -827,6 +827,25 @@ async def _sleep_for_timeout_async(timeout: float | str | httpx.Timeout):
         await asyncio.sleep(timeout.connect)
 
 
+class _AdmissionReservation(BaseModel):
+    input_tokens: int | None = None
+
+
+class _AdmissionMetadata(BaseModel):
+    user_api_key_budget_reservation: _AdmissionReservation | None = None
+
+
+def admission_input_tokens(kwargs: Mapping[str, object]) -> int | None:
+    reservations: Final = (
+        _AdmissionMetadata.model_validate(kwargs.get(key) or {}).user_api_key_budget_reservation
+        for key in ("litellm_metadata", "metadata")
+    )
+    return next(
+        (reservation.input_tokens for reservation in reservations if reservation and reservation.input_tokens),
+        None,
+    )
+
+
 def mock_completion(
     model: str,
     messages: list,
@@ -838,6 +857,7 @@ def mock_completion(
     logging=None,
     custom_llm_provider=None,
     timeout: float | str | httpx.Timeout | None = None,
+    prompt_tokens: int | None = None,
     **kwargs,
 ):
     """
@@ -953,13 +973,16 @@ def mock_completion(
                 ChatCompletionMessageToolCall(**tool_call) for tool_call in mock_tool_calls
             ]
 
+        usage_prompt_tokens: Final = (
+            prompt_tokens if prompt_tokens is not None else DEFAULT_MOCK_RESPONSE_PROMPT_TOKEN_COUNT
+        )
         setattr(
             model_response,
             "usage",
             Usage(
-                prompt_tokens=DEFAULT_MOCK_RESPONSE_PROMPT_TOKEN_COUNT,
+                prompt_tokens=usage_prompt_tokens,
                 completion_tokens=DEFAULT_MOCK_RESPONSE_COMPLETION_TOKEN_COUNT,
-                total_tokens=DEFAULT_MOCK_RESPONSE_PROMPT_TOKEN_COUNT + DEFAULT_MOCK_RESPONSE_COMPLETION_TOKEN_COUNT,
+                total_tokens=usage_prompt_tokens + DEFAULT_MOCK_RESPONSE_COMPLETION_TOKEN_COUNT,
             ),
         )
 
@@ -5542,6 +5565,7 @@ def completion(
                 custom_llm_provider=custom_llm_provider,
                 mock_timeout=mock_timeout,
                 timeout=timeout,
+                prompt_tokens=admission_input_tokens(cast(Mapping[str, object], kwargs)),
             )
 
         ## RESPONSES API BRIDGE LOGIC ## - check if model has 'mode: responses' in litellm.model_cost map
diff --git a/litellm/proxy/spend_tracking/budget_reservation.py b/litellm/proxy/spend_tracking/budget_reservation.py
index b469cd70d76..61d82fb6158 100644
--- a/litellm/proxy/spend_tracking/budget_reservation.py
+++ b/litellm/proxy/spend_tracking/budget_reservation.py
@@ -318,6 +318,7 @@ async def reserve_budget_for_request(
         "entries": applied_entries,
         "finalized": False,
         "input_cost": min(float(input_cost or 0.0), reservation_cost),
+        "input_tokens": max(input_token_counts.values(), default=None),
     }
 
 
diff --git a/tests/test_litellm/proxy/spend_tracking/test_budget_reservation.py b/tests/test_litellm/proxy/spend_tracking/test_budget_reservation.py
index f272361062b..23eb297b47f 100644
--- a/tests/test_litellm/proxy/spend_tracking/test_budget_reservation.py
+++ b/tests/test_litellm/proxy/spend_tracking/test_budget_reservation.py
@@ -64,6 +64,16 @@ async def test_non_exempt_llm_route_still_reserves_budget():
     assert reservation["reserved_cost"] > 0
 
 
+@pytest.mark.asyncio
+async def test_reservation_carries_the_admission_input_token_count():
+    reservation: Final = await _reserve("/v1/responses")
+    expected: Final = litellm.token_counter(model="gpt-4o", text="hello")
+
+    assert reservation is not None
+    assert expected > 0
+    assert reservation["input_tokens"] == expected
+
+
 ANTHROPIC_MESSAGES: Final = [{"role": "user", "content": "hello!!!"}]
 COUNT_TOKENS_REQUESTS: Final[tuple[tuple[str, dict[str, object]], ...]] = (
     ("/v1/messages/count_tokens", {"model": "claude-sonnet-5", "messages": ANTHROPIC_MESSAGES}),
diff --git a/tests/test_litellm/test_main.py b/tests/test_litellm/test_main.py
index de6322f27ee..39ee5b57455 100644
--- a/tests/test_litellm/test_main.py
+++ b/tests/test_litellm/test_main.py
@@ -2322,6 +2322,32 @@ def test_image_edit_merges_headers_and_extra_headers():
     assert "extra_headers" not in handler_kwargs["image_edit_optional_request_params"]
 
 
+@pytest.mark.parametrize("metadata_key", ("metadata", "litellm_metadata"))
+def test_mock_completion_usage_reports_admission_input_tokens(metadata_key: str):
+    response = litellm.completion(
+        model="anthropic/claude-sonnet-5",
+        messages=[{"role": "user", "content": "hello"}],
+        mock_response="ok",
+        api_key="mock",
+        **{metadata_key: {"user_api_key_budget_reservation": {"reserved_cost": 1.0, "input_tokens": 51234}}},
+    )
+
+    assert response.usage.prompt_tokens == 51234
+    assert response.usage.total_tokens == 51234 + response.usage.completion_tokens
+
+
+def test_mock_completion_usage_falls_back_to_default_without_admission_count():
+    response = litellm.completion(
+        model="anthropic/claude-sonnet-5",
+        messages=[{"role": "user", "content": "hello"}],
+        mock_response="ok",
+        api_key="mock",
+        metadata={"user_api_key_budget_reservation": {"reserved_cost": 1.0}},
+    )
+
+    assert response.usage.prompt_tokens == litellm_main.DEFAULT_MOCK_RESPONSE_PROMPT_TOKEN_COUNT
+
+
 def test_mock_completion_stream_with_model_response():
     """Test that mock_completion correctly handles stream=True with a ModelResponse as mock_response."""
     from litellm import completion