diff --git a/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py b/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
index 35495d59610..8fc76886008 100644
--- a/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
+++ b/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
@@ -212,6 +212,11 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
                     ),
                     status_code=400,
                 )
+            mapped_effort = (
+                AnthropicMessagesConfig._normalize_xhigh_effort_for_max_model(
+                    model, mapped_effort
+                )
+            )
             gate_error = AnthropicConfig._validate_effort_for_model(
                 model, mapped_effort
             )
@@ -223,6 +228,35 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             existing_output_config.setdefault("effort", mapped_effort)
             optional_params["output_config"] = existing_output_config
 
+    @staticmethod
+    def _normalize_xhigh_effort_for_max_model(model: str, effort: str) -> str:
+        """Return ``max`` when a model supports max effort but not xhigh."""
+        from litellm.llms.anthropic.chat.transformation import AnthropicConfig
+
+        if effort != "xhigh":
+            return effort
+        if AnthropicConfig._supports_effort_level(model, "xhigh"):
+            return effort
+        if AnthropicConfig._supports_effort_level(model, "max"):
+            return "max"
+        return effort
+
+    @staticmethod
+    def _normalize_explicit_output_config_xhigh_effort(
+        model: str, optional_params: Dict
+    ) -> None:
+        """Normalize explicit ``output_config.effort=xhigh`` when ``max`` is supported."""
+        output_config = optional_params.get("output_config")
+        if not isinstance(output_config, dict):
+            return
+        effort = output_config.get("effort")
+        if not isinstance(effort, str):
+            return
+
+        output_config["effort"] = (
+            AnthropicMessagesConfig._normalize_xhigh_effort_for_max_model(model, effort)
+        )
+
     @staticmethod
     def _translate_legacy_thinking_for_adaptive_model(
         model: str, optional_params: Dict
@@ -274,6 +308,11 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
                 status_code=400,
             )
 
+        self._normalize_explicit_output_config_xhigh_effort(
+            model=model,
+            optional_params=anthropic_messages_optional_request_params,
+        )
+
         self._translate_reasoning_effort_to_anthropic(
             model=model,
             optional_params=anthropic_messages_optional_request_params,
diff --git a/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_reasoning_effort_translation.py b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_reasoning_effort_translation.py
index 83716b8c8d3..50e4c4bead6 100644
--- a/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_reasoning_effort_translation.py
+++ b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_reasoning_effort_translation.py
@@ -99,28 +99,27 @@ def test_invalid_reasoning_effort_raises_400(bad_effort):
 
 
 @pytest.mark.parametrize(
-    "model,bad_effort",
+    "model",
     [
-        ("claude-opus-4-6", "xhigh"),
-        ("bedrock/invoke/us.anthropic.claude-opus-4-6-v1", "xhigh"),
-        ("claude-sonnet-4-6", "xhigh"),
+        "claude-opus-4-6",
+        "bedrock/invoke/us.anthropic.claude-opus-4-6-v1",
+        "claude-sonnet-4-6",
     ],
 )
-def test_reasoning_effort_unsupported_tier_raises_400_messages(model, bad_effort):
+def test_reasoning_effort_xhigh_normalizes_to_max_messages(model):
     config = AnthropicMessagesConfig()
-    optional_params = {"max_tokens": 1024, "reasoning_effort": bad_effort}
+    optional_params = {"max_tokens": 1024, "reasoning_effort": "xhigh"}
 
-    with pytest.raises(AnthropicError) as exc_info:
-        config.transform_anthropic_messages_request(
-            model=model,
-            messages=[{"role": "user", "content": "Hello"}],
-            anthropic_messages_optional_request_params=optional_params,
-            litellm_params={},
-            headers={},
-        )
+    result = config.transform_anthropic_messages_request(
+        model=model,
+        messages=[{"role": "user", "content": "Hello"}],
+        anthropic_messages_optional_request_params=optional_params,
+        litellm_params={},
+        headers={},
+    )
 
-    assert exc_info.value.status_code == 400
-    assert "not supported by this model" in str(exc_info.value)
+    output_config = result.get("output_config")
+    assert isinstance(output_config, dict) and output_config.get("effort") == "max"
 
 
 @pytest.mark.parametrize(
@@ -146,6 +145,43 @@ def test_reasoning_effort_max_accepted_on_sonnet_46_messages(model):
     assert isinstance(output_config, dict) and output_config.get("effort") == "max"
 
 
+@pytest.mark.parametrize(
+    "model",
+    [
+        "claude-sonnet-4-6",
+        "bedrock/invoke/us.anthropic.claude-sonnet-4-6",
+    ],
+)
+def test_explicit_output_config_xhigh_normalizes_to_max_messages(model):
+    config = AnthropicMessagesConfig()
+    optional_params = {"max_tokens": 1024, "output_config": {"effort": "xhigh"}}
+
+    result = config.transform_anthropic_messages_request(
+        model=model,
+        messages=[{"role": "user", "content": "Hello"}],
+        anthropic_messages_optional_request_params=optional_params,
+        litellm_params={},
+        headers={},
+    )
+
+    assert result.get("output_config") == {"effort": "max"}
+
+
+def test_explicit_output_config_xhigh_preserved_when_supported_messages():
+    config = AnthropicMessagesConfig()
+    optional_params = {"max_tokens": 1024, "output_config": {"effort": "xhigh"}}
+
+    result = config.transform_anthropic_messages_request(
+        model="claude-opus-4-7",
+        messages=[{"role": "user", "content": "Hello"}],
+        anthropic_messages_optional_request_params=optional_params,
+        litellm_params={},
+        headers={},
+    )
+
+    assert result.get("output_config") == {"effort": "xhigh"}
+
+
 def test_explicit_output_config_wins_over_reasoning_effort():
     config = AnthropicMessagesConfig()
     optional_params = {