diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index e32c1279261..72f53b469cd 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -1146,7 +1146,7 @@ class ChatAnthropic(BaseChatModel):
     model: str = Field(alias="model_name")
     """Model name to use."""
 
-    max_tokens: int = Field(default=1024, alias="max_tokens_to_sample")
+    max_tokens: Optional[int] = Field(default=None, alias="max_tokens_to_sample")
     """Denotes the number of tokens to predict per generation."""
 
     temperature: Optional[float] = None
@@ -1276,6 +1276,29 @@ class ChatAnthropic(BaseChatModel):
             ls_params["ls_stop"] = ls_stop
         return ls_params
 
+    @model_validator(mode="before")
+    @classmethod
+    def validate_max_tokens(cls, values: dict[str, Any]) -> Any:
+        """Validate max_tokens.
+
+        Can find the Max Tokens limits here: https://docs.anthropic.com/en/docs/about-claude/models/overview#model-comparison-table
+        """
+        if values.get("max_tokens") is None and values.get("model"):
+            if "claude-opus-4" in values.get("model", ""):
+                values["max_tokens"] = 32000
+            elif "claude-sonnet-4" in values.get(
+                "model", ""
+            ) or "claude-3-7-sonnet" in values.get("model", ""):
+                values["max_tokens"] = 64000
+            elif "claude-3-5-sonnet" in values.get(
+                "model", ""
+            ) or "claude-3-5-haiku" in values.get("model", ""):
+                values["max_tokens"] = 8192
+            # leaves us with "claude-3-haiku"
+            else:
+                values["max_tokens"] = 4096
+        return values
+
     @model_validator(mode="before")
     @classmethod
     def build_extra(cls, values: dict) -> Any:
diff --git a/libs/partners/anthropic/tests/cassettes/TestAnthropicStandard.test_stream_time.yaml.gz b/libs/partners/anthropic/tests/cassettes/TestAnthropicStandard.test_stream_time.yaml.gz
index 10a3e400719..af60833e15a 100644
Binary files a/libs/partners/anthropic/tests/cassettes/TestAnthropicStandard.test_stream_time.yaml.gz and b/libs/partners/anthropic/tests/cassettes/TestAnthropicStandard.test_stream_time.yaml.gz differ
diff --git a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
index 93605b4dded..a626e8a81bd 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -62,6 +62,45 @@ def test_anthropic_client_caching() -> None:
     assert llm1._client._client is not llm5._client._client
 
 
+def test_validate_max_tokens() -> None:
+    """Test the validate_max_tokens function through class initialization."""
+    # Test claude-opus-4 models
+    llm = ChatAnthropic(model="claude-opus-4-20250514", anthropic_api_key="test")
+    assert llm.max_tokens == 32000
+
+    # Test claude-sonnet-4 models
+    llm = ChatAnthropic(model="claude-sonnet-4-latest", anthropic_api_key="test")
+    assert llm.max_tokens == 64000
+
+    # Test claude-3-7-sonnet models
+    llm = ChatAnthropic(model="claude-3-7-sonnet-latest", anthropic_api_key="test")
+    assert llm.max_tokens == 64000
+
+    # Test claude-3-5-sonnet models
+    llm = ChatAnthropic(model="claude-3-5-sonnet-latest", anthropic_api_key="test")
+    assert llm.max_tokens == 8192
+
+    # Test claude-3-5-haiku models
+    llm = ChatAnthropic(model="claude-3-5-haiku-latest", anthropic_api_key="test")
+    assert llm.max_tokens == 8192
+
+    # Test claude-3-haiku models (should default to 4096)
+    llm = ChatAnthropic(model="claude-3-haiku-latest", anthropic_api_key="test")
+    assert llm.max_tokens == 4096
+
+    # Test that existing max_tokens values are preserved
+    llm = ChatAnthropic(
+        model="claude-3-5-sonnet-latest", max_tokens=2048, anthropic_api_key="test"
+    )
+    assert llm.max_tokens == 2048
+
+    # Test that explicitly set max_tokens values are preserved
+    llm = ChatAnthropic(
+        model="claude-3-5-sonnet-latest", max_tokens=4096, anthropic_api_key="test"
+    )
+    assert llm.max_tokens == 4096
+
+
 @pytest.mark.requires("anthropic")
 def test_anthropic_model_name_param() -> None:
     llm = ChatAnthropic(model_name="foo")  # type: ignore[call-arg, call-arg]