diff --git a/libs/langchain_v1/langchain/agents/middleware/summarization.py b/libs/langchain_v1/langchain/agents/middleware/summarization.py
index 42d2760b4e1..6c1091152c1 100644
--- a/libs/langchain_v1/langchain/agents/middleware/summarization.py
+++ b/libs/langchain_v1/langchain/agents/middleware/summarization.py
@@ -141,7 +141,7 @@ Example:
 
 def _get_approximate_token_counter(model: BaseChatModel) -> TokenCounter:
     """Tune parameters of approximate token counter based on model type."""
-    if model._llm_type == "anthropic-chat":  # noqa: SLF001
+    if model._llm_type.startswith("anthropic-chat"):  # noqa: SLF001
         # 3.3 was estimated in an offline experiment, comparing with Claude's token-counting
         # API: https://platform.claude.com/docs/en/build-with-claude/token-counting
         return partial(