I have a decorator to add support for slots: https://github.com/ericvsmith/dataclasses/blob/master/datacl... (although I'll admit I haven't tested it in a while).

The reason it's not an option by default is because it would be the one case where the decorator would have to return a new class, and I didn't want to do that on the first version. As it is, @dataclass just modifies an existing class. I might bite the bullet add a slots option, and we've had discussions on adding a language feature to automatically add slots to a class, based on annotations and maybe some other magic. If we did that, we wouldn't need to return a new class. But it's not a front-burner task for me.