diff --git a/litellm/llms/openai/chat/gpt_5_transformation.py b/litellm/llms/openai/chat/gpt_5_transformation.py
index 05c003c8b7..e491770a24 100644
--- a/litellm/llms/openai/chat/gpt_5_transformation.py
+++ b/litellm/llms/openai/chat/gpt_5_transformation.py
@@ -40,11 +40,16 @@ class OpenAIGPT5Config(OpenAIGPTConfig):
         
         gpt-5.1/5.2 support temperature when reasoning_effort="none",
         unlike base gpt-5 which only supports temperature=1. Excludes
-        pro variants which keep stricter knobs.
+        pro variants which keep stricter knobs and gpt-5.2-chat variants
+        which only support temperature=1.
         """
         model_name = model.split("/")[-1]
         is_gpt_5_1 = model_name.startswith("gpt-5.1")
-        is_gpt_5_2 = model_name.startswith("gpt-5.2") and "pro" not in model_name
+        is_gpt_5_2 = (
+            model_name.startswith("gpt-5.2")
+            and "pro" not in model_name
+            and not model_name.startswith("gpt-5.2-chat")
+        )
         return is_gpt_5_1 or is_gpt_5_2
 
     @classmethod
diff --git a/litellm/proxy/middleware/in_flight_requests_middleware.py b/litellm/proxy/middleware/in_flight_requests_middleware.py
index e5e405fb07..d615640d87 100644
--- a/litellm/proxy/middleware/in_flight_requests_middleware.py
+++ b/litellm/proxy/middleware/in_flight_requests_middleware.py
@@ -6,7 +6,7 @@ Prometheus gauge `litellm_in_flight_requests`.
 """
 
 import os
-from typing import Any, Optional
+from typing import Optional
 
 from starlette.types import ASGIApp, Receive, Scope, Send
 
@@ -27,7 +27,7 @@ class InFlightRequestsMiddleware:
     """
 
     _in_flight: int = 0
-    _gauge: Optional[Any] = None
+    _gauge: Optional[object] = None
     _gauge_init_attempted: bool = False
 
     def __init__(self, app: ASGIApp) -> None:
@@ -41,13 +41,13 @@ class InFlightRequestsMiddleware:
         InFlightRequestsMiddleware._in_flight += 1
         gauge = InFlightRequestsMiddleware._get_gauge()
         if gauge is not None:
-            gauge.inc()  # type: ignore[attr-defined]
+            gauge.inc()  # type: ignore[union-attr]
         try:
             await self.app(scope, receive, send)
         finally:
             InFlightRequestsMiddleware._in_flight -= 1
             if gauge is not None:
-                gauge.dec()  # type: ignore[attr-defined]
+                gauge.dec()  # type: ignore[union-attr]
 
     @staticmethod
     def get_count() -> int:
@@ -55,14 +55,14 @@ class InFlightRequestsMiddleware:
         return InFlightRequestsMiddleware._in_flight
 
     @staticmethod
-    def _get_gauge() -> Optional[Any]:
+    def _get_gauge() -> Optional[object]:
         if InFlightRequestsMiddleware._gauge_init_attempted:
             return InFlightRequestsMiddleware._gauge
         InFlightRequestsMiddleware._gauge_init_attempted = True
         try:
             from prometheus_client import Gauge
 
-            kwargs: dict[str, Any] = {}
+            kwargs = {}
             if "PROMETHEUS_MULTIPROC_DIR" in os.environ:
                 # livesum aggregates across all worker processes in the scrape response
                 kwargs["multiprocess_mode"] = "livesum"
diff --git a/tests/test_litellm/llms/openai/test_gpt5_transformation.py b/tests/test_litellm/llms/openai/test_gpt5_transformation.py
index 386f264a4d..4ccde67409 100644
--- a/tests/test_litellm/llms/openai/test_gpt5_transformation.py
+++ b/tests/test_litellm/llms/openai/test_gpt5_transformation.py
@@ -267,7 +267,8 @@ def test_gpt5_1_model_detection(gpt5_config: OpenAIGPT5Config):
     assert gpt5_config.is_model_gpt_5_1_model("gpt-5.1-chat")
     assert gpt5_config.is_model_gpt_5_1_model("gpt-5.2")
     assert gpt5_config.is_model_gpt_5_1_model("gpt-5.2-2025-12-11")
-    assert gpt5_config.is_model_gpt_5_1_model("gpt-5.2-chat-latest")
+    assert not gpt5_config.is_model_gpt_5_1_model("gpt-5.2-chat")
+    assert not gpt5_config.is_model_gpt_5_1_model("gpt-5.2-chat-latest")
     assert not gpt5_config.is_model_gpt_5_1_model("gpt-5.2-pro")
     assert not gpt5_config.is_model_gpt_5_1_model("gpt-5")
     assert not gpt5_config.is_model_gpt_5_1_model("gpt-5-mini")
@@ -395,7 +396,38 @@ def test_gpt5_temperature_still_restricted(config: OpenAIConfig):
     assert params["temperature"] == 1.0
 
 
-def test_gpt5_2_pro_allows_reasoning_effort_xhigh(config: OpenAIConfig):
+def test_gpt5_2_chat_temperature_restricted(config: OpenAIConfig):
+    """Test that gpt-5.2-chat only supports temperature=1, like base gpt-5.
+
+    Regression test for https://github.com/BerriAI/litellm/issues/21911
+    """
+    # gpt-5.2-chat should reject non-1 temperature when drop_params=False
+    for model in ["gpt-5.2-chat", "gpt-5.2-chat-latest"]:
+        with pytest.raises(litellm.utils.UnsupportedParamsError):
+            config.map_openai_params(
+                non_default_params={"temperature": 0.7},
+                optional_params={},
+                model=model,
+                drop_params=False,
+            )
+
+        # temperature=1 should still work
+        params = config.map_openai_params(
+            non_default_params={"temperature": 1.0},
+            optional_params={},
+            model=model,
+            drop_params=False,
+        )
+        assert params["temperature"] == 1.0
+
+        # drop_params=True should silently drop non-1 temperature
+        params = config.map_openai_params(
+            non_default_params={"temperature": 0.5},
+            optional_params={},
+            model=model,
+            drop_params=True,
+        )
+        assert "temperature" not in params
     params = config.map_openai_params(
         non_default_params={"reasoning_effort": "xhigh"},
         optional_params={},