self.additional_kwargs, other.additional_kwargs
                ),
            )
        elif isinstance(other, BaseMessageChunk):
            return self.__class__(
                role=self.role,
                content=merge_content(self.content, other.content),
                additional_kwargs=self._merge_kwargs_dict(
                    self.additional_kwargs, other.additional_kwargs
                ),
            )
        else:
            return super().__add__(other)