---
upgrade:
  - |
    The `serialize_callback_handler` and `deserialize_callback_handler` utility functions have been removed.
    Use `serialize_callable` and `deserialize_callable` instead.

    For more information on `serialize_callable` and `deserialize_callable`, see the API reference:
    https://docs.haystack.deepset.ai/reference/utils-api#module-callable_serialization