diff --git a/activestorage/CHANGELOG.md b/activestorage/CHANGELOG.md
index ff0c20f263..c5fafc80ec 100644
--- a/activestorage/CHANGELOG.md
+++ b/activestorage/CHANGELOG.md
@@ -2,17 +2,17 @@
 
     ```ruby
     class User < ActiveRecord::Base
-      has_one_attached :avatar, variants: {
-        thumb: { resize: "100x100" },
-        medium: { resize: "300x300", monochrome: true }
-      }
+      has_one_attached :avatar do |attachable|
+        attachable.variant :thumb, resize: "100x100"
+        attachable.variant :medium, resize: "300x300", monochrome: true
+      end
     end
 
     class Gallery < ActiveRecord::Base
-      has_many_attached :photos, variants: {
-        thumb: { resize: "100x100" },
-        medium: { resize: "300x300", monochrome: true }
-      }
+      has_many_attached :photos do |attachable|
+        attachable.variant :thumb, resize: "100x100"
+        attachable.variant :medium, resize: "300x300", monochrome: true
+      end
     end
 
     <%= image_tag user.avatar.variant(:thumb) %>
diff --git a/activestorage/app/models/active_storage/attachment.rb b/activestorage/app/models/active_storage/attachment.rb
index 6910848285..01c4d1bd26 100644
--- a/activestorage/app/models/active_storage/attachment.rb
+++ b/activestorage/app/models/active_storage/attachment.rb
@@ -66,7 +66,7 @@ class ActiveStorage::Attachment < ActiveRecord::Base
     end
 
     def variants
-      record.attachment_reflections[name]&.options[:variants]
+      record.attachment_reflections[name]&.variants
     end
 end
 
diff --git a/activestorage/lib/active_storage/attached/model.rb b/activestorage/lib/active_storage/attached/model.rb
index 939dec37a6..9e809af5ba 100644
--- a/activestorage/lib/active_storage/attached/model.rb
+++ b/activestorage/lib/active_storage/attached/model.rb
@@ -40,7 +40,7 @@ module ActiveStorage
       #     has_one_attached :avatar, service: :s3
       #   end
       #
-      def has_one_attached(name, dependent: :purge_later, service: nil, variants: {})
+      def has_one_attached(name, dependent: :purge_later, service: nil)
         validate_service_configuration(name, service)
 
         generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
@@ -72,9 +72,10 @@ module ActiveStorage
           :has_one_attached,
           name,
           nil,
-          { dependent: dependent, service_name: service, variants: variants },
+          { dependent: dependent, service_name: service },
           self
         )
+        yield reflection if block_given?
         ActiveRecord::Reflection.add_attachment_reflection(self, name, reflection)
       end
 
@@ -110,7 +111,7 @@ module ActiveStorage
       #     has_many_attached :photos, service: :s3
       #   end
       #
-      def has_many_attached(name, dependent: :purge_later, service: nil, variants: {})
+      def has_many_attached(name, dependent: :purge_later, service: nil)
         validate_service_configuration(name, service)
 
         generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
@@ -159,9 +160,10 @@ module ActiveStorage
           :has_many_attached,
           name,
           nil,
-          { dependent: dependent, service_name: service, variants: variants },
+          { dependent: dependent, service_name: service },
           self
         )
+        yield reflection if block_given?
         ActiveRecord::Reflection.add_attachment_reflection(self, name, reflection)
       end
 
diff --git a/activestorage/lib/active_storage/reflection.rb b/activestorage/lib/active_storage/reflection.rb
index ce248c88b5..5bec40d2d3 100644
--- a/activestorage/lib/active_storage/reflection.rb
+++ b/activestorage/lib/active_storage/reflection.rb
@@ -2,9 +2,19 @@
 
 module ActiveStorage
   module Reflection
+    class HasAttachedReflection < ActiveRecord::Reflection::MacroReflection #:nodoc:
+      def variant(name, transformations)
+        variants[name] = transformations
+      end
+
+      def variants
+        @variants ||= {}
+      end
+    end
+
     # Holds all the metadata about a has_one_attached attachment as it was
     # specified in the Active Record class.
-    class HasOneAttachedReflection < ActiveRecord::Reflection::MacroReflection #:nodoc:
+    class HasOneAttachedReflection < HasAttachedReflection #:nodoc:
       def macro
         :has_one_attached
       end
@@ -12,7 +22,7 @@ module ActiveStorage
 
     # Holds all the metadata about a has_many_attached attachment as it was
     # specified in the Active Record class.
-    class HasManyAttachedReflection < ActiveRecord::Reflection::MacroReflection #:nodoc:
+    class HasManyAttachedReflection < HasAttachedReflection #:nodoc:
       def macro
         :has_many_attached
       end
diff --git a/activestorage/test/models/reflection_test.rb b/activestorage/test/models/reflection_test.rb
index d8cd2a0ec9..4e258eb8e9 100644
--- a/activestorage/test/models/reflection_test.rb
+++ b/activestorage/test/models/reflection_test.rb
@@ -14,7 +14,7 @@ class ActiveStorage::ReflectionTest < ActiveSupport::TestCase
     assert_equal :local, reflection.options[:service_name]
 
     reflection = User.reflect_on_attachment(:avatar_with_variants)
-    assert_instance_of Hash, reflection.options[:variants]
+    assert_instance_of Hash, reflection.variants
   end
 
   test "reflection on a singular attachment with the same name as an attachment on another model" do
@@ -33,7 +33,7 @@ class ActiveStorage::ReflectionTest < ActiveSupport::TestCase
     assert_equal :local, reflection.options[:service_name]
 
     reflection = User.reflect_on_attachment(:highlights_with_variants)
-    assert_instance_of Hash, reflection.options[:variants]
+    assert_instance_of Hash, reflection.variants
   end
 
   test "reflecting on all attachments" do
diff --git a/activestorage/test/test_helper.rb b/activestorage/test/test_helper.rb
index 5a866c3f95..47d468324c 100644
--- a/activestorage/test/test_helper.rb
+++ b/activestorage/test/test_helper.rb
@@ -119,11 +119,15 @@ class User < ActiveRecord::Base
 
   has_one_attached :avatar
   has_one_attached :cover_photo, dependent: false, service: :local
-  has_one_attached :avatar_with_variants, variants: { thumb: { resize: "100x100" } }
+  has_one_attached :avatar_with_variants do |attachable|
+    attachable.variant :thumb, resize: "100x100"
+  end
 
   has_many_attached :highlights
   has_many_attached :vlogs, dependent: false, service: :local
-  has_many_attached :highlights_with_variants, variants: { thumb: { resize: "100x100" } }
+  has_many_attached :highlights_with_variants do |attachable|
+    attachable.variant :thumb, resize: "100x100"
+  end
 end
 
 class Group < ActiveRecord::Base
diff --git a/guides/source/active_storage_overview.md b/guides/source/active_storage_overview.md
index 8b0104cd9e..6491adced8 100644
--- a/guides/source/active_storage_overview.md
+++ b/guides/source/active_storage_overview.md
@@ -332,11 +332,13 @@ class User < ApplicationRecord
 end
 ```
 
-You can configure specific variants per attachment using the `variants` option:
+You can configure specific variants per attachment by calling the `variant` method on yielded attachable object:
 
 ```ruby
 class User < ApplicationRecord
-  has_one_attached :avatar, variants: { thumb: { resize: "100x100" } }
+  has_one_attached :avatar do |attachable|
+    attachable.variant :thumb, resize: "100x100"
+  end
 end
 ```
 
@@ -396,11 +398,13 @@ class Message < ApplicationRecord
 end
 ```
 
-Configuring specific variants is done the same way as `has_one_attached`, by using the `variants` option:
+Configuring specific variants is done the same way as `has_one_attached`, by calling the `variant` method on the yielded attachable object:
 
 ```ruby
 class Message < ApplicationRecord
-  has_many_attached :images, variants: { thumb: { resize: "100x100" } }
+  has_many_attached :images do |attachable|
+    attachable.variant :thumb, resize: "100x100"
+  end
 end
 ```