fix(bedrock): forward anthropic-beta headers verbatim on the Claude platform messages path

litellm/llms/bedrock/claude_platform/messages_transformation.py

@@ -12,6 +12,9 @@ from .common_utils import BedrockClaudePlatformMixin, strip_claude_platform_rout
 
 
 class BedrockClaudePlatformMessagesConfig(BedrockClaudePlatformMixin, AnthropicMessagesConfig):
+    def should_filter_anthropic_beta_headers(self) -> bool:
+        return False
+
     def validate_anthropic_messages_environment(
         self,
         headers: dict,

tests/test_litellm/llms/bedrock/test_claude_platform_provider.py

@@ -313,6 +313,41 @@ async def test_anthropic_messages_routes_bedrock_claude_platform_to_messages_api
     assert requests[0]["body"]["model"] == "claude-sonnet-4-6"
 
 
+@pytest.mark.asyncio
+async def test_anthropic_messages_bedrock_claude_platform_forwards_anthropic_beta_verbatim():
+    import litellm
+
+    requests = []
+
+    async def mock_post(self, url, data=None, headers=None, **kwargs):
+        requests.append(_capture_request(url=url, headers=headers or {}, data=data))
+        return _anthropic_response(url)
+
+    try:
+        with patch(
+            "litellm.llms.custom_httpx.http_handler.AsyncHTTPHandler.post",
+            new=mock_post,
+        ):
+            await litellm.anthropic_messages(
+                model="bedrock/claude_platform/claude-sonnet-4-6",
+                messages=[{"role": "user", "content": "hello"}],
+                max_tokens=10,
+                mcp_servers=[{"type": "url", "url": "https://mcp.example.com/mcp", "name": "example"}],
+                api_base="https://aws-external-anthropic.us-west-2.api.aws",
+                api_key="fake-platform-key",
+                workspace_id="wrkspc_test",
+                extra_headers={"anthropic-beta": "prompt-caching-scope-2026-01-05,mcp-client-2025-11-20"},
+            )
+    finally:
+        await litellm.close_litellm_async_clients()
+
+    assert len(requests) == 1
+    assert requests[0]["headers"]["anthropic-beta"] == "mcp-client-2025-11-20,prompt-caching-scope-2026-01-05"
+    assert requests[0]["body"]["mcp_servers"] == [
+        {"type": "url", "url": "https://mcp.example.com/mcp", "name": "example"}
+    ]
+
+
 def test_sigv4_no_duplicate_content_type_when_caller_sets_lowercase():
     """
     Regression: get_anthropic_headers() supplies "content-type" (lowercase).

tests/unit/llms/github_copilot/messages/test_github_copilot_messages_transformation.py

@@ -272,13 +272,11 @@ def test_github_copilot_config_disables_anthropic_beta_filtering():
     because github_copilot has no entry in the beta headers config; a regression
     here would silently disable header-gated Anthropic features for Copilot."""
     from litellm.anthropic_beta_headers_manager import update_headers_with_filtered_beta
-    from litellm.llms.anthropic.experimental_pass_through.messages.transformation import (
-        AnthropicMessagesConfig,
-    )
+    from litellm.llms.azure_ai.anthropic.messages_transformation import AzureAnthropicMessagesConfig
 
     config = GithubCopilotAnthropicMessagesConfig()
     assert config.should_filter_anthropic_beta_headers() is False
-    assert AnthropicMessagesConfig().should_filter_anthropic_beta_headers() is True
+    assert AzureAnthropicMessagesConfig().should_filter_anthropic_beta_headers() is True
 
     config.authenticator = MagicMock()
     config.authenticator.get_api_key.return_value = "gh.test-key"

tests/unit/llms/openai_like/messages/test_openai_like_anthropic_messages_transformation.py

@@ -268,12 +268,10 @@ def test_request_maps_reasoning_effort_to_thinking(config):
 
 
 def test_passthrough_disables_anthropic_beta_filtering(config):
-    from litellm.llms.anthropic.experimental_pass_through.messages.transformation import (
-        AnthropicMessagesConfig,
-    )
+    from litellm.llms.azure_ai.anthropic.messages_transformation import AzureAnthropicMessagesConfig
 
     assert config.should_filter_anthropic_beta_headers() is False
-    assert AnthropicMessagesConfig().should_filter_anthropic_beta_headers() is True
+    assert AzureAnthropicMessagesConfig().should_filter_anthropic_beta_headers() is True
 
 
 def test_anthropic_beta_survives_provider_filter_on_passthrough_path(config):