feat(anthropic): add metadata support to Anthropic Messages passthrough

litellm/llms/anthropic/experimental_pass_through/messages/transformation.py

@@ -68,8 +68,8 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             "speed",
             "output_config",
             "reasoning_effort",
-            # TODO: Add Anthropic `metadata` support
-            # "metadata",
+            
+            "metadata",
         ]
 
     def _remove_scope_from_cache_control(self, anthropic_messages_request: dict) -> None:

tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_messages_metadata.py

@@ -0,0 +1,49 @@
+"""
+Tests for Anthropic Messages passthrough metadata support.
+
+Related issue: https://github.com/BerriAI/litellm/issues/30663
+"""
+
+import pytest
+
+from litellm.llms.anthropic.experimental_pass_through.messages.transformation import (
+    AnthropicMessagesConfig,
+)
+
+
+class TestAnthropicMessagesMetadataSupport:
+    """Test that metadata is properly supported in Anthropic Messages passthrough."""
+
+    def setup_method(self):
+        self.config = AnthropicMessagesConfig()
+
+    def test_metadata_in_supported_params(self):
+        """Verify 'metadata' is listed in supported Anthropic Messages params."""
+        supported_params = self.config.get_supported_anthropic_messages_params(
+            model="claude-sonnet-4-20250514"
+        )
+        assert "metadata" in supported_params, (
+            "'metadata' should be in supported params for Anthropic Messages passthrough"
+        )
+
+    def test_metadata_appears_exactly_once(self):
+        """Verify 'metadata' is not duplicated in the supported params list."""
+        supported_params = self.config.get_supported_anthropic_messages_params(
+            model="claude-sonnet-4-20250514"
+        )
+        assert supported_params.count("metadata") == 1
+
+    def test_core_params_still_present(self):
+        """Regression: ensure adding metadata did not remove existing params."""
+        supported_params = self.config.get_supported_anthropic_messages_params(
+            model="claude-sonnet-4-20250514"
+        )
+        expected_core_params = [
+            "messages",
+            "model",
+            "system",
+            "max_tokens",
+            "temperature",
+        ]
+        for param in expected_core_params:
+            assert param in supported_params