diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index 9a63afd5cc0..bfd5dff9f47 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -3,7 +3,7 @@ import json
 import re
 import time
 from collections.abc import Callable, Mapping, Sequence
-from types import MappingProxyType
+from types import BuiltinFunctionType, FunctionType, MappingProxyType
 from typing import TYPE_CHECKING, Any, ClassVar, Final, NoReturn, cast
 
 import httpx
@@ -493,7 +493,26 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
 
     @classmethod
     def get_config(cls, *, model: str | None = None):
-        config: Final = super().get_config()
+        # defaults configured on the base class (litellm.AnthropicConfig(max_tokens=...)) live on
+        # AnthropicConfig itself and must keep reaching subclass requests (vertex/azure claude)
+        base: Final = {
+            k: v
+            for k, v in AnthropicConfig.__dict__.items()
+            if not k.startswith("_")
+            and not isinstance(
+                v,
+                (
+                    FunctionType,
+                    BuiltinFunctionType,
+                    classmethod,
+                    staticmethod,
+                    property,
+                ),
+            )
+            and v is not None
+            and not callable(v)
+        }
+        config: Final = {**base, **super().get_config()}
 
         # anthropic requires a default value for max_tokens
         if config.get("max_tokens") is None:
@@ -2385,7 +2404,7 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             optional_params["tools"] = tools
 
         ## Load Config
-        config: Final = litellm.AnthropicConfig.get_config(model=model)
+        config: Final = self.get_config(model=model)
         for k, v in config.items():
             if (
                 k not in optional_params
diff --git a/litellm/llms/vertex_ai/vertex_ai_partner_models/anthropic/transformation.py b/litellm/llms/vertex_ai/vertex_ai_partner_models/anthropic/transformation.py
index 29253359003..fde1dd18752 100644
--- a/litellm/llms/vertex_ai/vertex_ai_partner_models/anthropic/transformation.py
+++ b/litellm/llms/vertex_ai/vertex_ai_partner_models/anthropic/transformation.py
@@ -11,6 +11,7 @@ from litellm.litellm_core_utils.prompt_templates.image_handling import RemoteMed
 from litellm.llms.base_llm.chat.transformation import LiteLLMLoggingObj
 from litellm.types.llms.openai import AllMessageValues
 from litellm.types.utils import ModelResponse
+from litellm.utils import get_max_tokens
 
 from ....anthropic.chat.transformation import AnthropicConfig
 from .output_params_utils import sanitize_vertex_anthropic_output_params
@@ -62,6 +63,16 @@ class VertexAIAnthropicConfig(AnthropicConfig):
     def should_strip_billing_metadata(self) -> bool:
         return True
 
+    @staticmethod
+    def get_max_tokens_for_model(model: str | None = None) -> int:
+        if model is not None:
+            vertex_key: Final = f"vertex_ai/{model}"
+            if vertex_key in litellm.model_cost:  # pyright: ignore[reportUnknownMemberType]  # registry is dynamically typed
+                vertex_max: Final = get_max_tokens(vertex_key)
+                if vertex_max is not None:
+                    return vertex_max
+        return AnthropicConfig.get_max_tokens_for_model(model)
+
     def _add_context_management_beta_headers(self, beta_set: set, context_management: dict) -> None:
         """
         Add context_management beta headers to the beta_set.
diff --git a/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_transformation.py b/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_transformation.py
index 21bda6f0345..06cafbf4307 100644
--- a/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_transformation.py
+++ b/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_transformation.py
@@ -1185,3 +1185,44 @@ def test_refusal_stop_details_kept_through_vertex_anthropic_transform():
     provider_fields: Final = result.choices[0].message.provider_specific_fields
     assert provider_fields["stop_reason"] == "refusal"
     assert provider_fields["stop_details"] == ANTHROPIC_DOCS_REFUSAL_MESSAGE["stop_details"]
+
+def test_vertex_ai_anthropic_versioned_model_default_max_tokens(local_model_cost_map):
+    config = VertexAIAnthropicConfig()
+    data = config.transform_request(
+        model="claude-haiku-4-5@20251001",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={},
+        litellm_params={},
+        headers={},
+    )
+    assert data["max_tokens"] == 64000
+
+    unversioned = config.transform_request(
+        model="claude-haiku-4-5",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={},
+        litellm_params={},
+        headers={},
+    )
+    assert unversioned["max_tokens"] == 64000
+
+
+def test_vertex_ai_anthropic_base_config_defaults_reach_subclass(local_model_cost_map):
+    from litellm import AnthropicConfig
+
+    AnthropicConfig(max_tokens=123, temperature=0.5)
+    try:
+        data = VertexAIAnthropicConfig().transform_request(
+            model="claude-haiku-4-5@20251001",
+            messages=[{"role": "user", "content": "hi"}],
+            optional_params={},
+            litellm_params={},
+            headers={},
+        )
+    finally:
+        for attr in ("max_tokens", "temperature"):
+            if attr in AnthropicConfig.__dict__:
+                delattr(AnthropicConfig, attr)
+
+    assert data["max_tokens"] == 123
+    assert data["temperature"] == 0.5