Handle 404 with Ember Data, pseudo code: see route.js, application_adapter.js, router.js (given a response.status = 404) the router would redirect to a 404 route.

application_adapter.js

App.ApplicationAdapter = DS.RESTAdapter.extend({
  ajaxError: function(jqXHR) {
    var error = this._super(jqXHR),
      errors = {};

    if (jqXHR && jqXHR.status === 422) {
      var jsonErrors = Ember.$.parseJSON(jqXHR.responseText)["errors"];

      forEach(Ember.keys(jsonErrors), function (key) {
        errors[Ember.String.camelize(key)] = jsonErrors[key];
      });

      return new DS.InvalidError(errors);
    } else if (jqXHR && jqXHR.status === 404) {
      errors['404'] = 'Not Found';
      return new DS.InvalidError(errors);
    } else {
      return error;
    }
  }
});

route.js

App.ThingDetailRoute = Em.Route.extend({
  model: function(params, transition) {
    return this.store.find('thing', params.thing_id).then(
      (function(_this) {
        return function(model) {
          return _this.store.push('thing', model);
        };
      })(this),
      (function(_this) {
        return function(invalid) {
          if (invalid.errors && invalid.errors['404']) {
            return _this.transitionTo('not-found', invalid);
          }
        };
      })(this));
  }
});

router.js

App.Router.map(function() {
  this.resource('thing', {path: '/thing'}, function() {
    this.route('detail', {path: '/:thing_id'});
  });
  this.route('not-found', {path: '/*path'});
});

Shouldn't you handle the error part in the route's action hooks already baked error action ?

@shadow-fox yeah that is an option too: http://emberjs.com/guides/routing/loading-and-error-substates/#toc_code-error-code-substates ; could use a specific ErrorRoute too