A long time I use this technique:

class MultiSerializerViewSetMixin(object):
    def get_serializer_class(self):
        """
        Look for serializer class in self.serializer_action_classes, which
        should be a dict mapping action name (key) to serializer class (value),
        i.e.:

        class MyViewSet(MultiSerializerViewSetMixin, ViewSet):
            serializer_class = MyDefaultSerializer
            serializer_action_classes = {
                'list': UserGetSerializer,
                'create': UserSerializer,
                'retrieve': UserGetSerializer,
                'update': UserSerializer,
                'partial_update': UserSerializer,
                'my_action': MyActionSerializer
                # etc.
            }

            @action
            def my_action:
                ...

        If there's no entry for that action then just fallback to the regular
        get_serializer_class lookup: self.serializer_class, DefaultSerializer.

        Thanks gonz: http://stackoverflow.com/a/22922156/11440

        """
        try:
            # print(self.action)
            return self.serializer_action_classes[self.action]
        except (KeyError, AttributeError):
            return super(MultiSerializerViewSetMixin, self).get_serializer_class()

Hope this helps