From 756e939543e6bcf05b628659e3ec94c2cad4407e Mon Sep 17 00:00:00 2001
From: Greyson LaLonde <greyson@crewai.com>
Date: Thu, 19 Mar 2026 20:13:54 -0400
Subject: [PATCH] fix: serialize callbacks to string only in JSON mode to
 preserve closures during copy

---
 lib/crewai/src/crewai/types/callback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/crewai/src/crewai/types/callback.py b/lib/crewai/src/crewai/types/callback.py
index e8f2021ea..cfbff623c 100644
--- a/lib/crewai/src/crewai/types/callback.py
+++ b/lib/crewai/src/crewai/types/callback.py
@@ -91,6 +91,6 @@ def callable_to_string(fn: Callable[..., Any]) -> str:
 SerializableCallable = Annotated[
     Callable[..., Any],
     BeforeValidator(string_to_callable),
-    PlainSerializer(callable_to_string, return_type=str),
+    PlainSerializer(callable_to_string, return_type=str, when_used="json"),
     WithJsonSchema({"type": "string"}),
 ]