That's indeed true in California, but "at will" employment doesn't strictly require that. At-will employment means either side can terminate the employment arra

That's indeed true in California, but "at will" employment doesn't strictly require that. At-will employment means either side can terminate the employment arrangement for any or no cause, as distinguished from jurisdictions that require a reason for termination. It's still compatible with having a short notice period, e.g. requiring that employees give 2 weeks notice before quitting, and/or that employers give 2 weeks notice before termination.