diff --git a/tests/test_litellm/llms/azure/chat/test_azure_chat_gpt_transformation.py b/tests/test_litellm/llms/azure/chat/test_azure_chat_gpt_transformation.py
index 8df35a37514..7be4d6dfcf2 100644
--- a/tests/test_litellm/llms/azure/chat/test_azure_chat_gpt_transformation.py
+++ b/tests/test_litellm/llms/azure/chat/test_azure_chat_gpt_transformation.py
@@ -30,6 +30,19 @@ class TestAzureOpenAIConfig:
         assert not config._is_response_format_supported_model("gpt-35-turbo")
 
 
+    def test_prompt_cache_key_supported(self):
+        """Test that 'prompt_cache_key' is in supported params for Azure OpenAI chat completion models.
+
+        OpenAI's Chat Completions API supports prompt_cache_key for cache routing optimization.
+        """
+        config = AzureOpenAIConfig()
+        supported_params = config.get_supported_openai_params("gpt-4.1-nano")
+        assert "prompt_cache_key" in supported_params
+
+        supported_params = config.get_supported_openai_params("gpt-4.1")
+        assert "prompt_cache_key" in supported_params
+
+
 def test_map_openai_params_with_preview_api_version():
     config = AzureOpenAIConfig()
     non_default_params = {
diff --git a/tests/test_litellm/llms/openai/chat/test_openai_gpt_transformation.py b/tests/test_litellm/llms/openai/chat/test_openai_gpt_transformation.py
index 5f087363797..c0695bf3588 100644
--- a/tests/test_litellm/llms/openai/chat/test_openai_gpt_transformation.py
+++ b/tests/test_litellm/llms/openai/chat/test_openai_gpt_transformation.py
@@ -2,9 +2,10 @@
 Tests for OpenAI GPT transformation (litellm/llms/openai/chat/gpt_transformation.py)
 """
 
-import pytest
-import sys
 import os
+import sys
+
+import pytest
 
 sys.path.insert(0, os.path.abspath("../../../../.."))
 
@@ -73,6 +74,17 @@ class TestOpenAIGPTConfig:
         for param in base_expected_params:
             assert param in supported_params, f"Expected '{param}' in supported params"
 
+    def test_prompt_cache_key_supported(self):
+        """Test that 'prompt_cache_key' is in supported params for OpenAI chat completion models.
+
+        OpenAI's Chat Completions API supports prompt_cache_key for cache routing optimization.
+        """
+        supported_params = self.config.get_supported_openai_params("gpt-4.1-nano")
+        assert "prompt_cache_key" in supported_params
+
+        supported_params = self.config.get_supported_openai_params("gpt-4.1")
+        assert "prompt_cache_key" in supported_params
+
 
 class TestGetOptionalParamsIntegration:
     """Integration tests using litellm.get_optional_params()"""
@@ -123,3 +135,14 @@ class TestGetOptionalParamsIntegration:
         # Both should include user
         assert regular_params.get("user") == "my-end-user"
         assert responses_params.get("user") == "my-end-user"
+
+    def test_prompt_cache_key_in_optional_params(self):
+        """Test that 'prompt_cache_key' flows through get_optional_params for OpenAI models."""
+        from litellm.utils import get_optional_params
+
+        optional_params = get_optional_params(
+            model="gpt-4.1-nano",
+            custom_llm_provider="openai",
+            prompt_cache_key="test-cache-key-123",
+        )
+        assert optional_params.get("prompt_cache_key") == "test-cache-key-123"