diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index 92330a03ac0..85fd7c7fd0d 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -1305,11 +1305,17 @@ class ChatAnthropic(BaseChatModel):
     def validate_max_tokens(cls, values: dict[str, Any]) -> Any:
         """Validate max_tokens."""
         if values.get("max_tokens") is None and values.get("model"):
-            if "claude-opus-4" in values.get("model"):
+            if "claude-opus-4" in values.get("model", ""):
                 values["max_tokens"] = 32000
-            elif values.get("model") in ["claude-sonnet-4", "claude-3-7-sonnet"]:
+            elif (
+                "claude-sonnet-4" in values.get("model", "")
+                or "claude-3-7-sonnet" in values.get("model", "")
+            ):
                 values["max_tokens"] = 64000
-            elif values.get("model") in ["claude-3-5-sonnet", "claude-3-5-haiku"]:
+            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-3-5-opus", "claude-3-haiku"
             else: