diff --git a/tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/gpt_oss/test_vertex_ai_gpt_oss_transformation.py b/tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/gpt_oss/test_vertex_ai_gpt_oss_transformation.py
index fb5529d4752..b6d6402bcd4 100644
--- a/tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/gpt_oss/test_vertex_ai_gpt_oss_transformation.py
+++ b/tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/gpt_oss/test_vertex_ai_gpt_oss_transformation.py
@@ -15,6 +15,14 @@ from litellm.llms.vertex_ai.vertex_ai_partner_models.gpt_oss.transformation impo
 )
 
 
+@pytest.fixture(autouse=True)
+def _reset_litellm_http_client_cache():
+    """Ensure each test gets a fresh async HTTP client mock."""
+    from litellm import in_memory_llm_clients_cache
+
+    in_memory_llm_clients_cache.flush_cache()
+
+
 @pytest.fixture(autouse=True)
 def clean_vertex_env():
     """Clear Google/Vertex AI environment variables before each test to prevent test isolation issues."""