diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index cd5bb731717..2b3647d944c 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -1534,11 +1534,15 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
                 f"Invalid effort value: {effort}. Must be one of: "
                 f"'high', 'medium', 'low', 'xhigh', 'max'"
             )
-        # ``max`` is Claude Opus 4.6 only (not Sonnet 4.6, not Opus 4.5/4.7).
-        # Keep this hardcoded so the error message is specific and stable.
-        if effort == "max" and not self._is_opus_4_6_model(model):
+        # ``max`` is supported by Claude Opus 4.6 and Opus 4.7 (not Sonnet 4.6,
+        # not Opus 4.5). The upstream Anthropic API accepts effort=max on both
+        # Opus 4.6 and 4.7, so we keep both substring checks here for
+        # date-variant tolerance (e.g. claude-opus-4-7-20260408). See #25957.
+        if effort == "max" and not (
+            self._is_opus_4_6_model(model) or self._is_opus_4_7_model(model)
+        ):
             raise ValueError(
-                f"effort='max' is only supported by Claude Opus 4.6. "
+                f"effort='max' is only supported by Claude Opus 4.6 and 4.7. "
                 f"Got model: {model}"
             )
         # ``xhigh`` is data-driven via ``supports_xhigh_reasoning_effort`` so
diff --git a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
index a7f5f92ab05..e44c4791726 100644
--- a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
+++ b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
@@ -1654,7 +1654,7 @@ def test_max_effort_rejected_for_opus_45():
     messages = [{"role": "user", "content": "Test"}]
 
     with pytest.raises(
-        ValueError, match="effort='max' is only supported by Claude Opus 4.6"
+        ValueError, match="effort='max' is only supported by Claude Opus 4.6 and 4.7"
     ):
         optional_params = {"output_config": {"effort": "max"}}
         config.transform_request(
@@ -2213,12 +2213,12 @@ def test_reasoning_effort_does_not_set_output_config_for_older_models():
 
 
 def test_max_effort_rejected_for_sonnet_46():
-    """Test that effort='max' is rejected for Sonnet 4.6 (only Opus 4.6 supports max)."""
+    """Test that effort='max' is rejected for Sonnet 4.6 (Sonnet 4.6 doesn't support max)."""
     config = AnthropicConfig()
     messages = [{"role": "user", "content": "Test"}]
 
     with pytest.raises(
-        ValueError, match="effort='max' is only supported by Claude Opus 4.6"
+        ValueError, match="effort='max' is only supported by Claude Opus 4.6 and 4.7"
     ):
         config.transform_request(
             model="claude-sonnet-4-6-20260219",
@@ -2245,6 +2245,27 @@ def test_max_effort_accepted_for_opus_46():
     assert result["output_config"]["effort"] == "max"
 
 
+def test_max_effort_accepted_for_opus_47():
+    """Regression for #25957 - effort='max' must work for Opus 4.7.
+
+    Anthropic's Messages API accepts ``output_config.effort='max'`` on
+    ``claude-opus-4-7-*`` models. The previous hardcoded ``_is_opus_4_6_model``
+    guard rejected the request before it ever reached Anthropic.
+    """
+    config = AnthropicConfig()
+    messages = [{"role": "user", "content": "Test"}]
+
+    result = config.transform_request(
+        model="claude-opus-4-7-20260416",
+        messages=messages,
+        optional_params={"output_config": {"effort": "max"}},
+        litellm_params={},
+        headers={},
+    )
+
+    assert result["output_config"]["effort"] == "max"
+
+
 def test_effort_beta_header_not_injected_for_46_models():
     """
     Test that is_effort_used returns False for Claude 4.6 models.