diff --git a/langextract/providers/patterns.py b/langextract/providers/patterns.py
index 9fd18cab..353df357 100644
--- a/langextract/providers/patterns.py
+++ b/langextract/providers/patterns.py
@@ -28,6 +28,8 @@
     r'^gpt4\.',
     r'^gpt-5',
     r'^gpt5\.',
+    r'^gpt-3\.5',
+    r'^o[1-9]',
 )
 OPENAI_PRIORITY = 10
 
diff --git a/tests/patterns_test.py b/tests/patterns_test.py
new file mode 100644
index 00000000..a4d2bebe
--- /dev/null
+++ b/tests/patterns_test.py
@@ -0,0 +1,62 @@
+# Copyright 2025 Google LLC.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for the built-in provider routing patterns in patterns.py."""
+
+from absl.testing import absltest
+
+from langextract import providers as providers_module
+from langextract.providers import openai as openai_provider
+from langextract.providers import router
+
+
+class OpenAIPatternsTest(absltest.TestCase):
+  """Regression test for issue #492: o-series and gpt-3.5 model IDs
+  previously matched no provider pattern and raised InferenceConfigError."""
+
+  def setUp(self):
+    super().setUp()
+    router.clear()
+    providers_module._builtins_loaded = False  # pylint: disable=protected-access
+    providers_module.load_builtins_once()
+
+  def tearDown(self):
+    super().tearDown()
+    router.clear()
+    providers_module._builtins_loaded = False  # pylint: disable=protected-access
+
+  def test_reasoning_and_legacy_openai_models_resolve_to_openai_provider(self):
+    model_ids = [
+        "o1",
+        "o1-mini",
+        "o3",
+        "o3-mini",
+        "o4-mini",
+        "gpt-3.5-turbo",
+    ]
+    for model_id in model_ids:
+      with self.subTest(model_id=model_id):
+        resolved = router.resolve(model_id)
+        self.assertEqual(resolved, openai_provider.OpenAILanguageModel)
+
+  def test_ollama_gpt_oss_pattern_is_unaffected(self):
+    # Guards against the new `^o[1-9]` OpenAI pattern accidentally
+    # colliding with Ollama's `^gpt-oss` pattern (it shouldn't - different
+    # literal prefixes - but this pins the expected behavior explicitly).
+    resolved = router.resolve("gpt-oss:20b")
+    self.assertNotEqual(resolved, openai_provider.OpenAILanguageModel)
+
+
+if __name__ == "__main__":
+  absltest.main()