diff --git a/src/notewise/_constants.py b/src/notewise/_constants.py
index 0ea456b..c097135 100644
--- a/src/notewise/_constants.py
+++ b/src/notewise/_constants.py
@@ -25,7 +25,7 @@
 BOOL_SETTING_TRUTHY_VALUES = frozenset({"1", "true", "yes", "on"})
 BOOL_SETTING_FALSY_VALUES = frozenset({"0", "false", "no", "off"})
 PYDANTIC_RESPONSE_USAGE_WARNING_PATTERN = (
-    r"(?s)^Pydantic serializer warnings:.*ResponseAPIUsage"
+    r"(?s)^Pydantic serializer warnings:.*(ResponseAPIUsage|ResponsesAPIResponse)"
 )
 GITHUB_REPOSITORY_OWNER = "whoisjayd"
 GITHUB_REPOSITORY_NAME = "notewise"
diff --git a/src/notewise/llm/provider.py b/src/notewise/llm/provider.py
index edcf86b..a21fa52 100644
--- a/src/notewise/llm/provider.py
+++ b/src/notewise/llm/provider.py
@@ -50,6 +50,10 @@ def suppress_litellm_noise() -> None:
         verbose_logger.propagate = False
         for handler in list(verbose_logger.handlers):
             verbose_logger.removeHandler(handler)
+        if not verbose_logger.handlers:
+            # Avoid Python's `logging.lastResort` handler printing LiteLLM's
+            # non-blocking internal logging exceptions to stderr.
+            verbose_logger.addHandler(logging.NullHandler())
     warnings.filterwarnings(
         "ignore",
         message=PYDANTIC_RESPONSE_USAGE_WARNING_PATTERN,
diff --git a/tests/unit/llm/test_providers.py b/tests/unit/llm/test_providers.py
index d453a38..b1fd4d5 100644
--- a/tests/unit/llm/test_providers.py
+++ b/tests/unit/llm/test_providers.py
@@ -640,6 +640,29 @@ def test_suppress_litellm_noise_suppresses_response_usage_warning(self):
         finally:
             warnings.filters[:] = original_filters
 
+    def test_suppress_litellm_noise_suppresses_response_payload_warning(self):
+        """LiteLLM's Responses response serializer warnings should stay off the TTY."""
+        original_filters = warnings.filters[:]
+        try:
+            suppress_litellm_noise()
+
+            with warnings.catch_warnings(record=True) as caught:
+                warnings.warn_explicit(
+                    "Pydantic serializer warnings:\n"
+                    "  PydanticSerializationUnexpectedValue("
+                    "Expected `ResponsesAPIResponse` - serialized value may not be "
+                    "as expected [field_name='response', input_value={}, "
+                    "input_type=dict])",
+                    UserWarning,
+                    filename="pydantic/main.py",
+                    lineno=464,
+                    module="pydantic.main",
+                )
+
+            assert caught == []
+        finally:
+            warnings.filters[:] = original_filters
+
     def test_suppress_litellm_noise_sets_verbose_logger_level(self):
         """LiteLLM runtime should not attach terminal handlers."""
         runtime = MagicMock()
@@ -653,6 +676,32 @@ def test_suppress_litellm_noise_sets_verbose_logger_level(self):
         assert runtime.verbose_logger.propagate is False
         runtime.verbose_logger.removeHandler.assert_called_once()
 
+    def test_suppress_litellm_noise_installs_null_handler(self):
+        """LiteLLM's verbose logger should not fall back to logging.lastResort."""
+        logger_name = "LiteLLM-test-nullhandler"
+        litellm_logger = logging.getLogger(logger_name)
+        original_handlers = list(litellm_logger.handlers)
+        original_propagate = litellm_logger.propagate
+        original_level = litellm_logger.level
+        try:
+            litellm_logger.handlers.clear()
+            litellm_logger.propagate = False
+            litellm_logger.setLevel(logging.NOTSET)
+
+            runtime = SimpleNamespace(verbose_logger=litellm_logger)
+            with patch("notewise.llm.provider.litellm", runtime):
+                suppress_litellm_noise()
+
+            assert litellm_logger.propagate is False
+            assert any(
+                isinstance(handler, logging.NullHandler)
+                for handler in litellm_logger.handlers
+            )
+        finally:
+            litellm_logger.handlers[:] = original_handlers
+            litellm_logger.propagate = original_propagate
+            litellm_logger.setLevel(original_level)
+
     def test_extract_usage_handles_invalid_values(self):
         """Non-numeric usage payloads should fail closed to zero values."""
         provider = LLMProvider("gpt-4o")