diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 81d9968..1a4c597 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -12,12 +12,18 @@ jobs:
           - '3.2'
           - '3.3'
           - '3.4'
+          - '4.0'
         gemfile:
           - gemfiles/Gemfile.rails70
           - gemfiles/Gemfile.rails71
           - gemfiles/Gemfile.rails72
           - gemfiles/Gemfile.rails80
+          - gemfiles/Gemfile.rails81
         exclude:
+          # rails 8.1 requires ruby >= 3.2
+          # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
+          - ruby-version: '3.1'
+            gemfile: 'gemfiles/Gemfile.rails81'
           # rails 8.0 requires ruby >= 3.2
           # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
           - ruby-version: '3.1'
@@ -26,6 +32,8 @@ jobs:
           # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
           - ruby-version: '3.4'
             gemfile: 'gemfiles/Gemfile.rails70'
+          - ruby-version: '4.0'
+            gemfile: 'gemfiles/Gemfile.rails70'
 
     name: Ruby ${{ matrix.ruby-version }} / Bundle ${{ matrix.gemfile }}
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b46318e..b7962a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 ## [Unreleased]
-*no unreleased changes*
+### Fixed
+* Support Rails 8.1, Ruby 4.0
+* capistrano: Support bundler 4 with capistrano 2
 
 ## 7.3.5 / 2025-10-16
 ### Fixed
diff --git a/gemfiles/Gemfile.rails81 b/gemfiles/Gemfile.rails81
new file mode 100644
index 0000000..9382562
--- /dev/null
+++ b/gemfiles/Gemfile.rails81
@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+gemspec path: '..'
+
+gem 'activesupport', '~> 8.1.0'
diff --git a/lib/ndr_dev_support/capistrano/bundler_deployment.rb b/lib/ndr_dev_support/capistrano/bundler_deployment.rb
new file mode 100644
index 0000000..11b7c17
--- /dev/null
+++ b/lib/ndr_dev_support/capistrano/bundler_deployment.rb
@@ -0,0 +1,90 @@
+# Support capistrano 2 with old (< 4) and new (>= 4) bundler versions
+#
+# Add "require 'ndr_dev_support/capistrano/ndr_model'" in your Capistrano deploy.rb,
+# but remove calls to "require 'bundler/capistrano'", and
+# Bundler will be activated after each new deployment.
+
+if Gem::Version.new(Bundler::VERSION).release < Gem::Version.new('4.0')
+  require 'bundler/capistrano' unless defined?(Bundler::Deployment)
+else
+  # Redefine deployment helpers for Capistrano 2, previously defined in bundler < 4
+  # cf. https://blog.rubygems.org/2025/12/03/upgrade-to-rubygems-bundler-4.html
+  # Code copied from bundler 2 source files bundler/deployment.rb and bundler/capistrano.rb
+  # rubocop:disable Style/Documentation, Metrics/AbcSize, Metrics/MethodLength, Style/StringLiterals, Style/SymbolArray, Style/RaiseArgs, Layout/EmptyLineAfterGuardClause, Style/StringLiteralsInInterpolation, Style/Lambda
+  module Bundler
+    class Deployment
+      def self.define_task(context, task_method = :task, opts = {})
+        if defined?(Capistrano) && context.is_a?(Capistrano::Configuration)
+          context_name = "capistrano"
+          role_default = "{:except => {:no_release => true}}"
+          error_type = ::Capistrano::CommandError
+        else
+          context_name = "vlad"
+          role_default = "[:app]"
+          error_type = ::Rake::CommandFailedError
+        end
+
+        roles = context.fetch(:bundle_roles, false)
+        opts[:roles] = roles if roles
+
+        context.send :namespace, :bundle do
+          send :desc, <<-DESC
+            Install the current Bundler environment. By default, gems will be \
+            installed to the shared/bundle path. Gems in the development and \
+            test group will not be installed. The install command is executed \
+            with the --deployment and --quiet flags. If the bundle cmd cannot \
+            be found then you can override the bundle_cmd variable to specify \
+            which one it should use. The base path to the app is fetched from \
+            the :latest_release variable. Set it for custom deploy layouts.
+
+            You can override any of these defaults by setting the variables shown below.
+
+            N.B. bundle_roles must be defined before you require 'bundler/#{context_name}' \
+            in your deploy.rb file.
+
+              set :bundle_gemfile,  "Gemfile"
+              set :bundle_dir,      File.join(fetch(:shared_path), 'bundle')
+              set :bundle_flags,    "--deployment --quiet"
+              set :bundle_without,  [:development, :test]
+              set :bundle_with,     [:mysql]
+              set :bundle_cmd,      "bundle" # e.g. "/opt/ruby/bin/bundle"
+              set :bundle_roles,    #{role_default} # e.g. [:app, :batch]
+          DESC
+          send task_method, :install, opts do
+            bundle_cmd     = context.fetch(:bundle_cmd, "bundle")
+            bundle_flags   = context.fetch(:bundle_flags, "--deployment --quiet")
+            bundle_dir     = context.fetch(:bundle_dir, File.join(context.fetch(:shared_path), "bundle"))
+            bundle_gemfile = context.fetch(:bundle_gemfile, "Gemfile")
+            bundle_without = [*context.fetch(:bundle_without, [:development, :test])].compact
+            bundle_with    = [*context.fetch(:bundle_with, [])].compact
+            app_path = context.fetch(:latest_release)
+            if app_path.to_s.empty?
+              raise error_type.new("Cannot detect current release path - make sure you have deployed at least once.")
+            end
+            args = ["--gemfile #{File.join(app_path, bundle_gemfile)}"]
+            args << "--path #{bundle_dir}" unless bundle_dir.to_s.empty?
+            args << bundle_flags.to_s
+            args << "--without #{bundle_without.join(" ")}" unless bundle_without.empty?
+            args << "--with #{bundle_with.join(" ")}" unless bundle_with.empty?
+
+            run "cd #{app_path} && #{bundle_cmd} install #{args.join(" ")}"
+          end
+        end
+      end
+    end
+  end
+
+  # Capistrano task for Bundler.
+  require "capistrano/version"
+
+  if defined?(Capistrano::Version) && Gem::Version.new(Capistrano::Version).release >= Gem::Version.new("3.0")
+    raise "For Capistrano 3.x integration, please use https://github.com/capistrano/bundler"
+  end
+
+  Capistrano::Configuration.instance(:must_exist).load do
+    before "deploy:finalize_update", "bundle:install"
+    Bundler::Deployment.define_task(self, :task, except: { no_release: true })
+    set :rake, lambda { "#{fetch(:bundle_cmd, "bundle")} exec rake" }
+  end
+  # rubocop:enable Style/Documentation, Metrics/AbcSize, Metrics/MethodLength, Style/StringLiterals, Style/SymbolArray, Style/RaiseArgs, Layout/EmptyLineAfterGuardClause, Style/StringLiteralsInInterpolation, Style/Lambda
+end
diff --git a/lib/ndr_dev_support/capistrano/ndr_model.rb b/lib/ndr_dev_support/capistrano/ndr_model.rb
index 7d25618..3059262 100644
--- a/lib/ndr_dev_support/capistrano/ndr_model.rb
+++ b/lib/ndr_dev_support/capistrano/ndr_model.rb
@@ -2,6 +2,7 @@
 
 # Discrete bits of functionality we use automatically:
 require_relative 'assets'
+require_relative 'bundler_deployment'
 require_relative 'deploy_secrets'
 require_relative 'install_ruby'
 require_relative 'macos_bsdtar'
diff --git a/ndr_dev_support.gemspec b/ndr_dev_support.gemspec
index 3742c20..fd6c0a7 100644
--- a/ndr_dev_support.gemspec
+++ b/ndr_dev_support.gemspec
@@ -44,7 +44,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'show_me_the_cookies'
 
   # CI server dependencies:
-  spec.add_dependency 'activesupport', '>= 6.1', '< 8.1'
+  spec.add_dependency 'activesupport', '>= 7.0', '< 8.2'
   spec.add_dependency 'brakeman', '>= 4.7.1'
   spec.add_dependency 'bundler-audit'
   spec.add_dependency 'github-linguist'