In the actual documentation, in the chapter which concern identifiers, there's always mention of the "generation" attribute of the GeneratedValue annotation. It's not "generation" but "generator".

Example at : http://docs.jboss.org/hibernate/orm/5.1/userguide/html_single/Hibernate_User_Guide.html#identifiers

@Entity
public class MyEntity {

    @Id
    @GeneratedValue( *generation *= SEQUENCE )
    public Integer id;

    ...
}