diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 559f536..c04a80e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -22,6 +22,7 @@ jobs:
     strategy:
       matrix:
         ruby-version: [3.4.4, 3.3.8, 3.2.8, 3.1.7]
+        grape-version: ['~> 2.3.0', '~> 3.0']
     steps:
       - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
@@ -29,5 +30,9 @@ jobs:
           ruby-version: ${{ matrix.ruby-version }}
       - name: Install dependencies
         run: bundle install --jobs 4 --retry 3
+        env:
+          GRAPE_VERSION: ${{ matrix.grape-version }}
       - name: Run tests
         run: bundle exec rake
+        env:
+          GRAPE_VERSION: ${{ matrix.grape-version }}
diff --git a/lib/grape-active_model_serializers/options_builder.rb b/lib/grape-active_model_serializers/options_builder.rb
index e415d40..8975214 100644
--- a/lib/grape-active_model_serializers/options_builder.rb
+++ b/lib/grape-active_model_serializers/options_builder.rb
@@ -49,11 +49,7 @@ def default_root_options
       end
 
       def innermost_scope
-        if endpoint.respond_to?(:namespace_stackable)
-          endpoint.namespace_stackable(:namespace).last
-        else
-          endpoint.settings.peek[:namespace]
-        end
+        endpoint.inheritable_setting.namespace_stackable[:namespace]&.last
       end
 
       def meta_options