diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 994925a2..7b2d8a21 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,7 +13,7 @@ permissions:
 
 jobs:
   rubocop:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04 # no ubuntu-26.04 builds of Ruby 3.0/3.1 yet; revisit when ubuntu-latest moves
     steps:
       - uses: actions/checkout@v7
       - uses: ruby/setup-ruby@v1
@@ -24,11 +24,11 @@ jobs:
         run: bundle exec rubocop --parallel --format progress
 
   rspec:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04 # no ubuntu-26.04 builds of Ruby 3.0/3.1 yet; revisit when ubuntu-latest moves
     needs: ['rubocop']
     strategy:
       matrix:
-        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4']
+        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0']
     steps:
     - name: Check out branch
       uses: actions/checkout@v7
diff --git a/.github/workflows/danger-comment.yml b/.github/workflows/danger-comment.yml
index 8e15cb6c..02a589d2 100644
--- a/.github/workflows/danger-comment.yml
+++ b/.github/workflows/danger-comment.yml
@@ -7,5 +7,5 @@ on:
 
 jobs:
   comment:
-    uses: numbata/danger-pr-comment/.github/workflows/danger-comment.yml@v0.1.0
+    uses: numbata/danger-pr-comment/.github/workflows/danger-comment.yml@v0.1.1
     secrets: inherit
diff --git a/.github/workflows/danger.yml b/.github/workflows/danger.yml
index bd89a888..c510cdac 100644
--- a/.github/workflows/danger.yml
+++ b/.github/workflows/danger.yml
@@ -6,7 +6,7 @@ on:
 
 jobs:
   danger:
-    uses: numbata/danger-pr-comment/.github/workflows/danger-run.yml@v0.1.0
+    uses: numbata/danger-pr-comment/.github/workflows/danger-run.yml@v0.1.1
     secrets: inherit
     with:
       ruby-version: '3.4'
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d997acc4..8442405c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,8 @@
-### Next release
+### 1.1.1 (Next)
 
 #### Fixes
 
+* [#411](https://github.com/ruby-grape/grape-entity/pull/411): Fix CI on Ruby 3.0 (pin `json` below 3.0, `git` below 6, newer RuboCop directives), add Ruby 4.0 to the test matrix - [@numbata](https://github.com/numbata).
 * Your contribution here.
 
 #### Features
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6023a84e..77750c1c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -52,7 +52,7 @@ Document any external behavior in the [README](README.md).
 
 #### Update Changelog
 
-Add a line to [CHANGELOG](CHANGELOG.md) under *Next Release*. Make it look like every other line, including your name and link to your Github account.
+Add a line to [CHANGELOG](CHANGELOG.md) under the unreleased `(Next)` section. Make it look like every other line, including your name and link to your Github account.
 
 #### Commit Changes
 
diff --git a/Gemfile b/Gemfile
index c3a69c50..79caf54f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -6,13 +6,16 @@ gemspec
 
 group :development, :test do
   gem 'bundler'
+  # activesupport 7.1 (the newest on Ruby 3.0) passes `quirks_mode:` to JSON.generate, which json 3.0 removed
+  gem 'json', '< 3.0' if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('3.1')
   gem 'maruku'
+  gem 'ostruct' # no longer a default gem in Ruby 4.0
   gem 'pry' unless RUBY_PLATFORM.eql?('java') || RUBY_ENGINE.eql?('rbx')
   gem 'pry-byebug' unless RUBY_PLATFORM.eql?('java') || RUBY_ENGINE.eql?('rbx')
   gem 'rack-test'
   gem 'rake'
   gem 'rspec', '~> 3.9'
-  gem 'rubocop', '~> 1.0'
+  gem 'rubocop', '~> 1.90' # the disable-next directive needs 1.90
   gem 'yard'
 end
 
@@ -21,6 +24,8 @@ group :test do
   gem 'danger', require: false
   gem 'danger-changelog', require: false
   gem 'danger-pr-comment', require: false
+  # danger 9.6 references Git::Base, which git 6 no longer loads eagerly; drop once danger supports git 6
+  gem 'git', '< 6'
   gem 'growl'
   gem 'guard'
   gem 'guard-bundler'
diff --git a/RELEASING.md b/RELEASING.md
index 85d736da..3a0f3fa1 100644
--- a/RELEASING.md
+++ b/RELEASING.md
@@ -19,7 +19,7 @@ Increment the version, modify [lib/grape-entity/version.rb](lib/grape-entity/ver
 *  Increment the third number if the release has bug fixes and/or very minor features, only (eg. change `0.5.1` to `0.5.2`).
 *  Increment the second number if the release contains major features or breaking API changes (eg. change `0.5.1` to `0.4.0`).
 
-Change "Next Release" in [CHANGELOG.md](CHANGELOG.md) to the new version.
+Change the "(Next)" heading in [CHANGELOG.md](CHANGELOG.md) to the new version and release date.
 
 ```
 0.4.0 (2014-01-27)
@@ -52,8 +52,13 @@ Pushed grape-entity 0.4.0 to rubygems.org.
 Add the next release to [CHANGELOG.md](CHANGELOG.md).
 
 ```
-Next Release
-============
+### X.Y.Z (Next)
+
+#### Fixes
+
+* Your contribution here.
+
+#### Features
 
 * Your contribution here.
 ```
diff --git a/lib/grape_entity/entity.rb b/lib/grape_entity/entity.rb
index 4b409c13..93c87c08 100644
--- a/lib/grape_entity/entity.rb
+++ b/lib/grape_entity/entity.rb
@@ -190,7 +190,7 @@ def self.inherited(subclass)
     #   field, typically the value is a hash with two fields, type and desc.
     # @option options :merge This option allows you to merge an exposed field to the root
     #
-    # rubocop:disable Layout/LineLength
+    # rubocop:disable-next Layout/LineLength
     def self.expose(*args, &block)
       options = merge_options(args.last.is_a?(Hash) ? args.pop : {})
 
@@ -217,7 +217,6 @@ def self.expose(*args, &block)
       @nesting_stack ||= []
       args.each { |attribute| build_exposure_for_attribute(attribute, @nesting_stack, options, block) }
     end
-    # rubocop:enable Layout/LineLength
 
     def self.build_exposure_for_attribute(attribute, nesting_stack, options, block)
       exposure_list = nesting_stack.empty? ? root_exposures : nesting_stack.last.nested_exposures
diff --git a/lib/grape_entity/exposure/nesting_exposure/nested_exposures.rb b/lib/grape_entity/exposure/nesting_exposure/nested_exposures.rb
index 80076ed8..72752377 100644
--- a/lib/grape_entity/exposure/nesting_exposure/nested_exposures.rb
+++ b/lib/grape_entity/exposure/nesting_exposure/nested_exposures.rb
@@ -36,7 +36,7 @@ def clear
             @exposures.clear
           end
 
-          # rubocop:disable Style/DocumentDynamicEvalDefinition
+          # rubocop:disable-next Style/DocumentDynamicEvalDefinition
           %i[
             each
             to_ary to_a
@@ -56,7 +56,6 @@ def #{name}(*args, &block)
               end
             RUBY
           end
-          # rubocop:enable Style/DocumentDynamicEvalDefinition
 
           # Determine if we have any nesting exposures with the same name.
           def deep_complex_nesting?(entity)
diff --git a/spec/grape_entity/entity_spec.rb b/spec/grape_entity/entity_spec.rb
index aa497857..446b30e3 100644
--- a/spec/grape_entity/entity_spec.rb
+++ b/spec/grape_entity/entity_spec.rb
@@ -33,13 +33,12 @@
         end
 
         it 'makes sure that :format_with as a proc cannot be used with a block' do
-          # rubocop:disable Style/BlockDelimiters
+          # rubocop:disable-next Style/BlockDelimiters
           expect {
             subject.expose :name, format_with: proc {} do
               p 'hi'
             end
           }.to raise_error ArgumentError
-          # rubocop:enable Style/BlockDelimiters
         end
 
         it 'makes sure unknown options are not silently ignored' do
@@ -2294,12 +2293,11 @@ class FriendEntity < Grape::Entity
             end
           end
 
-          # rubocop:disable Lint/EmptyBlock
+          # rubocop:disable-next Lint/EmptyBlock
           fresh_class.class_eval do
             expose :first_friend, using: EntitySpec::FriendEntity do |_user, _opts|
             end
           end
-          # rubocop:enable Lint/EmptyBlock
 
           rep = subject.value_for(:first_friend)
           expect(rep).to be_kind_of EntitySpec::FriendEntity