From cf5da620217636edec74f4eecdca72aac69133fe Mon Sep 17 00:00:00 2001
From: cthomas <caren@letta.com>
Date: Thu, 3 Apr 2025 11:51:08 -0700
Subject: [PATCH] fix: anthropic thinking tag nesting bug (#1548)

---
 letta/schemas/message.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/letta/schemas/message.py b/letta/schemas/message.py
index 65e5d84b..4881ab0e 100644
--- a/letta/schemas/message.py
+++ b/letta/schemas/message.py
@@ -670,6 +670,9 @@ class Message(BaseMessage):
 
         def add_xml_tag(string: str, xml_tag: Optional[str]):
             # NOTE: Anthropic docs recommends using <thinking> tag when using CoT + tool use
+            if f"<{xml_tag}>" in string and f"</{xml_tag}>" in string:
+                # don't nest if tags already exist
+                return string
             return f"<{xml_tag}>{string}</{xml_tag}" if xml_tag else string
 
         if self.role == "system":