Add changelog

changelog/3457.changed.md

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+# Reduce Call Tool Result Context Size by Allowing UTF-8 in JSON Serialization
+
+This PR changes tool result serialization to prevent UTF-8 code points from being escaped during serialization. This drastically reduces the context size when returning a response that contains languages other than English.
+
+We have been running a monkey-patched version in production and it helped us improve the agent accuracy and control cost better.
+
+```
+>>> data = { "message": "أهلًا بالعالم" }
+>>> json.dumps(data)
+'{"message": "\\u0623\\u0647\\u0644\\u064b\\u0627 \\u0628\\u0627\\u0644\\u0639\\u0627\\u0644\\u0645"}'
+>>> 
+>>> 
+>>> 
+>>> json.dumps(data, ensure_ascii=False)
+'{"message": "أهلًا بالعالم"}'
+```