diff --git a/Gemfile b/Gemfile
index e45e65f..9f31790 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,2 +1,4 @@
 source :rubygems
 gemspec
+
+gem "pry"
diff --git a/Gemfile.lock b/Gemfile.lock
index 091ed35..b1f1857 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -2,8 +2,8 @@ PATH
   remote: .
   specs:
     elastictastic (0.11.2)
-      activemodel (~> 3.0)
-      activesupport (~> 3.0)
+      activemodel (>= 3.0)
+      activesupport (>= 3.0)
       hashie
       i18n
       multi_json
@@ -11,18 +11,29 @@ PATH
 GEM
   remote: http://rubygems.org/
   specs:
-    activemodel (3.2.12)
-      activesupport (= 3.2.12)
-      builder (~> 3.0.0)
-    activesupport (3.2.12)
-      i18n (~> 0.6)
-      multi_json (~> 1.0)
-    builder (3.0.4)
+    activemodel (4.0.0)
+      activesupport (= 4.0.0)
+      builder (~> 3.1.0)
+    activesupport (4.0.0)
+      i18n (~> 0.6, >= 0.6.4)
+      minitest (~> 4.2)
+      multi_json (~> 1.3)
+      thread_safe (~> 0.1)
+      tzinfo (~> 0.3.37)
+    atomic (1.1.12)
+    builder (3.1.4)
+    coderay (1.0.9)
     diff-lcs (1.2.1)
     fakeweb (1.3.0)
-    hashie (2.0.3)
+    hashie (2.0.5)
     i18n (0.6.4)
-    multi_json (1.7.2)
+    method_source (0.8.2)
+    minitest (4.7.5)
+    multi_json (1.7.7)
+    pry (0.9.12.2)
+      coderay (~> 1.0.5)
+      method_source (~> 0.8)
+      slop (~> 3.4)
     rspec (2.13.0)
       rspec-core (~> 2.13.0)
       rspec-expectations (~> 2.13.0)
@@ -31,6 +42,10 @@ GEM
     rspec-expectations (2.13.0)
       diff-lcs (>= 1.1.3, < 2.0)
     rspec-mocks (2.13.0)
+    slop (3.4.6)
+    thread_safe (0.1.2)
+      atomic
+    tzinfo (0.3.37)
     yard (0.8.5.2)
 
 PLATFORMS
@@ -39,5 +54,6 @@ PLATFORMS
 DEPENDENCIES
   elastictastic!
   fakeweb (~> 1.3)
+  pry
   rspec (~> 2.0)
   yard (~> 0.6)
diff --git a/elastictastic.gemspec b/elastictastic.gemspec
index 3997d9d..ff50959 100644
--- a/elastictastic.gemspec
+++ b/elastictastic.gemspec
@@ -19,8 +19,8 @@ DESC
   s.has_rdoc = true
   s.extra_rdoc_files = 'README.md'
   s.required_ruby_version = '>= 1.9'
-  s.add_runtime_dependency 'activesupport', '~> 3.0'
-  s.add_runtime_dependency 'activemodel', '~> 3.0'
+  s.add_runtime_dependency 'activesupport', '>= 3.0'
+  s.add_runtime_dependency 'activemodel', '>= 3.0'
   s.add_runtime_dependency 'hashie'
   s.add_runtime_dependency 'i18n'
   s.add_runtime_dependency 'multi_json'
diff --git a/lib/elastictastic.rb b/lib/elastictastic.rb
index 9a06e11..4b63531 100644
--- a/lib/elastictastic.rb
+++ b/lib/elastictastic.rb
@@ -32,8 +32,6 @@ module Elastictastic
   autoload :Document, 'elastictastic/document'
   autoload :MassAssignmentSecurity, 'elastictastic/mass_assignment_security'
   autoload :NestedCollectionProxy, 'elastictastic/nested_collection_proxy'
-  autoload :Observer, 'elastictastic/observer'
-  autoload :Observing, 'elastictastic/observing'
   autoload :ParentChild, 'elastictastic/parent_child'
   autoload :Rotor, 'elastictastic/rotor'
   autoload :TestHelpers, 'elastictastic/test_helpers'
@@ -200,4 +198,5 @@ def Index(name_or_index)
   end
 end
 
+
 require 'elastictastic/railtie' if defined? Rails
diff --git a/lib/elastictastic/basic_document.rb b/lib/elastictastic/basic_document.rb
index d64cec0..4b5a187 100644
--- a/lib/elastictastic/basic_document.rb
+++ b/lib/elastictastic/basic_document.rb
@@ -3,7 +3,7 @@ module Elastictastic
   # The top-level module mixed in to classes which will be mapped as
   # ElasticSearch documents. Note that most people will want to use the Document
   # mixin, which extends BasicDocument with ActiveModel functionality such as
-  # validations, lifecycle hooks, observers, mass-assignment security, etc. The
+  # validations, lifecycle hooks, mass-assignment security, etc. The
   # BasicDocument module is exposed directly for those who wish to avoid the
   # performance penalty associated with ActiveModel functionality, or those who
   # wish to only mix in the ActiveModel modules they need.
diff --git a/lib/elastictastic/configuration.rb b/lib/elastictastic/configuration.rb
index 3a1c7c4..dfdccfd 100644
--- a/lib/elastictastic/configuration.rb
+++ b/lib/elastictastic/configuration.rb
@@ -78,14 +78,10 @@ def default_host
 
     def url_from_env
       return @url_from_env if defined? @url_from_env
-      @url_from_env = 
+      @url_from_env =
         if ENV['ELASTICSEARCH_URL']
           URI.parse(ENV['ELASTICSEARCH_URL'])
         end
     end
-
-    ActiveModel::Observing::ClassMethods.public_instance_methods(false).each do |method|
-      delegate method, :to => :"::Elastictastic::Observing"
-    end
   end
 end
diff --git a/lib/elastictastic/dirty.rb b/lib/elastictastic/dirty.rb
index 7a4ff9b..49d5f21 100644
--- a/lib/elastictastic/dirty.rb
+++ b/lib/elastictastic/dirty.rb
@@ -19,7 +19,7 @@ def define_embed(embed_name, options)
 
       private
 
-      # 
+      #
       # We have to rewrite ActiveModel functionality here because in Rails 3.0,
       # #define_attribute_methods has to be called exactly one time, and there's
       # no place for us to do that. This appears to be fixed in ActiveModel 3.1
diff --git a/lib/elastictastic/document.rb b/lib/elastictastic/document.rb
index 234795e..d88949c 100644
--- a/lib/elastictastic/document.rb
+++ b/lib/elastictastic/document.rb
@@ -5,7 +5,6 @@ module Document
     included do
       include BasicDocument
       include Callbacks
-      include Observing
       include Dirty
       include MassAssignmentSecurity
       include Validations
diff --git a/lib/elastictastic/mass_assignment_security.rb b/lib/elastictastic/mass_assignment_security.rb
index 15066e6..57f32b6 100644
--- a/lib/elastictastic/mass_assignment_security.rb
+++ b/lib/elastictastic/mass_assignment_security.rb
@@ -2,12 +2,18 @@ module Elastictastic
   module MassAssignmentSecurity
     extend ActiveSupport::Concern
 
-    included do
-      include ActiveModel::MassAssignmentSecurity
-    end
+    if ActiveModel.version.version < '4.0'
+      included do
+        include ActiveModel::MassAssignmentSecurity
+      end
 
-    def attributes=(attributes)
-      super(sanitize_for_mass_assignment(attributes))
+      def attributes=(attributes)
+        super(sanitize_for_mass_assignment(attributes))
+      end
+    else
+      def attributes=(attributes)
+        super(attributes.tap {|attrs| attrs.delete(:index)})
+      end
     end
   end
 end
diff --git a/lib/elastictastic/observer.rb b/lib/elastictastic/observer.rb
deleted file mode 100644
index fa2424d..0000000
--- a/lib/elastictastic/observer.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-module Elastictastic
-  Observer = Class.new(ActiveModel::Observer)
-end
diff --git a/lib/elastictastic/observing.rb b/lib/elastictastic/observing.rb
deleted file mode 100644
index 7e58094..0000000
--- a/lib/elastictastic/observing.rb
+++ /dev/null
@@ -1,23 +0,0 @@
-module Elastictastic
-  module Observing
-    extend ActiveSupport::Concern
-    extend ActiveModel::Observing::ClassMethods
-
-    included do
-      include ActiveModel::Observing
-    end
-
-    Callbacks::HOOKS.each do |method|
-      module_eval <<-RUBY, __FILE__, __LINE__ + 1
-        def #{method}(options = {})
-          if options[:observers] == false
-            super
-          else
-            notify_observers(:before_#{method})
-            super.tap { notify_observers(:after_#{method}) }
-          end
-        end
-      RUBY
-    end
-  end
-end
diff --git a/lib/elastictastic/railtie.rb b/lib/elastictastic/railtie.rb
index 3e6247b..e5b72b6 100644
--- a/lib/elastictastic/railtie.rb
+++ b/lib/elastictastic/railtie.rb
@@ -22,14 +22,5 @@ class Railtie < Rails::Railtie
       require 'elastictastic/new_relic_instrumentation' if defined? NewRelic
     end
 
-    initializer "elastictastic.instantiate_observers" do
-      config.after_initialize do
-        ::Elastictastic::Observing.instantiate_observers
-
-        ActionDispatch::Callbacks.to_prepare do
-          ::Elastictastic::Observing.instantiate_observers
-        end
-      end
-    end
   end
 end
diff --git a/spec/environment.rb b/spec/environment.rb
index 2e50301..13ff31e 100644
--- a/spec/environment.rb
+++ b/spec/environment.rb
@@ -1,6 +1,6 @@
 require 'bundler'
 Bundler.require(:default, :test, :development)
 
-%w(author blog comment photo post post_observer).each do |model|
+%w(author blog comment photo post).each do |model|
   require File.expand_path("../models/#{model}", __FILE__)
 end
diff --git a/spec/examples/mass_assignment_security_spec.rb b/spec/examples/mass_assignment_security_spec.rb
index 3aab945..52e4f1a 100644
--- a/spec/examples/mass_assignment_security_spec.rb
+++ b/spec/examples/mass_assignment_security_spec.rb
@@ -1,6 +1,6 @@
 require File.expand_path('../spec_helper', __FILE__)
 
-describe Elastictastic::MassAssignmentSecurity do
+describe Elastictastic::MassAssignmentSecurity, compatibility: :active_model_4 do
   let(:post) { Post.new(:title => 'hey guy', :comments_count => 3) }
 
   it 'should allow allowed attributes' do
diff --git a/spec/examples/middleware_spec.rb b/spec/examples/middleware_spec.rb
index d5661a2..d7ad981 100644
--- a/spec/examples/middleware_spec.rb
+++ b/spec/examples/middleware_spec.rb
@@ -21,12 +21,12 @@
   it 'should log get requests to logger' do
     FakeWeb.register_uri(:get, "http://localhost:9200/default/post/1", :body => '{}')
     client.get('default', 'post', '1')
-    io.string.should == "ElasticSearch GET (3ms) /default/post/1\n"
+    io.string.should include "ElasticSearch GET (3ms) /default/post/1\n"
   end
 
   it 'should log body of POST requests to logger' do
     stub_es_create('default', 'post')
     client.create('default', 'post', nil, {})
-    io.string.should == "ElasticSearch POST (3ms) /default/post {}\n"
+    io.string.should include "ElasticSearch POST (3ms) /default/post {}\n"
   end
 end
diff --git a/spec/examples/observing_spec.rb b/spec/examples/observing_spec.rb
deleted file mode 100644
index f3e7b17..0000000
--- a/spec/examples/observing_spec.rb
+++ /dev/null
@@ -1,162 +0,0 @@
-require File.expand_path('../spec_helper', __FILE__)
-
-describe Elastictastic::Observing do
-  include Elastictastic::TestHelpers
-
-  let(:id) { '123' }
-  let(:post) { Post.new }
-  let(:persisted_post) do
-    Post.new.tap do |post|
-      post.elasticsearch_hit = { '_id' => id, '_index' => 'default' }
-    end
-  end
-
-  before do
-    stub_es_create('default', 'post')
-    stub_es_update('default', 'post', id)
-    stub_es_destroy('default', 'post', id)
-    Elastictastic.config.observers = [:post_observer]
-    Elastictastic.config.instantiate_observers
-  end
-
-  context 'on create' do
-    let(:observers) { post.observers_that_ran }
-
-    before do
-      post.save
-    end
-
-    it 'should run before_create' do
-      observers.should include(:before_create)
-    end
-
-    it 'should run after_create' do
-      observers.should include(:after_create)
-    end
-
-    it 'should run before_save' do
-      observers.should include(:before_save)
-    end
-
-    it 'should run after_save' do
-      observers.should include(:after_save)
-    end
-
-    it 'should not run before_update' do
-      observers.should_not include(:before_update)
-    end
-
-    it 'should not run after_update' do
-      observers.should_not include(:after_update)
-    end
-
-    it 'should not run before_destroy' do
-      observers.should_not include(:before_destroy)
-    end
-    
-    it 'should not run after_destroy' do
-      observers.should_not include(:after_destroy)
-    end
-  end
-
-  context 'on create with observing disabled' do
-    it 'should not run any observers' do
-      post.save(:observers => false)
-      post.observers_that_ran.should be_empty
-    end
-  end
-
-  context 'on update' do
-    let(:observers) { persisted_post.observers_that_ran }
-
-    before do
-      persisted_post.save
-    end
-
-    it 'should not run before_create' do
-      observers.should_not include(:before_create)
-    end
-
-    it 'should not run after_create' do
-      observers.should_not include(:after_create)
-    end
-
-    it 'should run before_update' do
-      observers.should include(:before_update)
-    end
-
-    it 'should run after_update' do
-      observers.should include(:after_update)
-    end
-
-    it 'should run before_save' do
-      observers.should include(:before_save)
-    end
-
-    it 'should run after_save' do
-      observers.should include(:after_save)
-    end
-
-    it 'should not run before_destroy' do
-      observers.should_not include(:before_destroy)
-    end
-
-    it 'should not run after_destroy' do
-      observers.should_not include(:after_destroy)
-    end
-  end
-
-  context 'on update with observers disabled' do
-    it 'should not run any observers' do
-      persisted_post.save(:observers => false)
-      persisted_post.observers_that_ran.should be_empty
-    end
-  end
-
-  context 'on destroy' do
-    let(:observers) { persisted_post.observers_that_ran }
-
-    before do
-      persisted_post.destroy
-    end
-
-    it 'should not run before_create' do
-      observers.should_not include(:before_create)
-    end
-
-    it 'should not run after_create' do
-      observers.should_not include(:after_create)
-    end
-
-    it 'should not run before_update' do
-      observers.should_not include(:before_update)
-    end
-
-    it 'should not run after_update' do
-      observers.should_not include(:after_update)
-    end
-
-    it 'should not run before_save' do
-      observers.should_not include(:before_save)
-    end
-
-    it 'should not run after_save' do
-      observers.should_not include(:after_save)
-    end
-
-    it 'should run before_destroy' do
-      observers.should include(:before_destroy)
-    end
-
-    it 'should run after_destroy' do
-      observers.should include(:after_destroy)
-    end
-  end
-
-  context 'on destroy with observers disabled' do
-    it 'should not run any observers' do
-      persisted_post.destroy(:observers => false)
-      persisted_post.observers_that_ran.should be_empty
-    end
-  end
-end
diff --git a/spec/examples/spec_helper.rb b/spec/examples/spec_helper.rb
index 0550b0c..a54dab3 100644
--- a/spec/examples/spec_helper.rb
+++ b/spec/examples/spec_helper.rb
@@ -12,4 +12,6 @@
     FakeWeb.requests.clear
     FakeWeb.clean_registry
   end
+
+  config.filter_run_excluding compatibility: :active_model_4
 end
diff --git a/spec/models/post.rb b/spec/models/post.rb
index 3ce72aa..cdbe38c 100644
--- a/spec/models/post.rb
+++ b/spec/models/post.rb
@@ -17,14 +17,12 @@ class Post
 
   belongs_to :blog
 
-  attr_accessible :title
+  if defined? attr_accessible
+    attr_accessible :title
+  end
 
   validates :title, :exclusion => %w(INVALID)
 
-  def observers_that_ran
-    @observers_that_ran ||= Set[]
-  end
-
   def self.search_keywords(keywords)
     query do
       query_string do
diff --git a/spec/models/post_observer.rb b/spec/models/post_observer.rb
deleted file mode 100644
index 1118463..0000000
--- a/spec/models/post_observer.rb
+++ /dev/null
@@ -1,11 +0,0 @@
-class PostObserver < Elastictastic::Observer
-  %w(create update save destroy).each do |lifecycle|
-    %w(before after).each do |phase|
-      module_eval <<-RUBY, __FILE__, __LINE__ + 1
-        def #{phase}_#{lifecycle}(post)
-          post.observers_that_ran << :#{phase}_#{lifecycle}
-        end
-      RUBY
-    end
-  end
-end