diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0f74fb478..860f7da47 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,7 +15,7 @@ jobs:
       matrix:
         gemfile:
          - Gemfile
-        ruby: ["3.2", "3.3", "3.4"]
+        ruby: ["3.2", "3.3", "3.4", "4.0"]
     env:
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
     steps:
diff --git a/.ruby-version b/.ruby-version
index 7921bd0c8..1454f6ed4 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.8
+4.0.1
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cdb4ae21..b347a11b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## [Unreleased]
 
+- Add support for Ruby 4.0 [#434](https://github.com/Shopify/worldwide/pull/434)
+
 ---
 ## [1.22.0] - 2026-03-09
 - Add CLDR unit formatting support for 12 new measurement categories: area, duration, electric, energy, frequency, light, power, pressure, speed, temperature, digital, and graphics (~50 new unit keys with locale-aware formatting) [#436](https://github.com/Shopify/worldwide/pull/436)
diff --git a/Gemfile b/Gemfile
index 4d9556db3..6ec563bfa 100644
--- a/Gemfile
+++ b/Gemfile
@@ -20,7 +20,8 @@ group :development do
   gem "rubocop-shopify", require: false
   gem "rubocop", require: false
   gem "ruby-lsp", require: false
-  gem "pry-byebug", require: false
+  gem "debug", require: false
+  gem "benchmark", require: false
 end
 
 group :test do
diff --git a/Gemfile.lock b/Gemfile.lock
index 0dfd3b1a7..257214d32 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -16,6 +16,8 @@ PATH
     worldwide (1.22.0)
       activesupport (>= 7.0)
       i18n
+      logger
+      ostruct
       phonelib (~> 0.8)
 
 GEM
@@ -34,20 +36,29 @@ GEM
     ansi (1.5.0)
     ast (2.4.2)
     base64 (0.1.1)
+    benchmark (0.5.0)
     bigdecimal (3.1.4)
     builder (3.2.4)
-    byebug (11.1.3)
-    coderay (1.1.3)
-    concurrent-ruby (1.2.2)
+    concurrent-ruby (1.3.6)
     connection_pool (2.4.1)
+    debug (1.11.1)
+      irb (~> 1.10)
+      reline (>= 0.3.8)
     drb (2.1.1)
       ruby2_keywords
-    i18n (1.14.1)
+    erb (6.0.1)
+    i18n (1.14.8)
       concurrent-ruby (~> 1.0)
+    io-console (0.8.2)
+    irb (1.17.0)
+      pp (>= 0.6.0)
+      prism (>= 1.3.0)
+      rdoc (>= 4.0.0)
+      reline (>= 0.4.2)
     json (2.7.1)
     language_server-protocol (3.17.0.3)
-    method_source (1.1.0)
-    minitest (5.17.0)
+    logger (1.7.0)
+    minitest (5.27.0)
     minitest-focus (1.3.1)
       minitest (>= 4, < 6)
     minitest-reporters (1.5.0)
@@ -55,25 +66,24 @@ GEM
       builder
       minitest (>= 5.0)
       ruby-progressbar
-    mocha (2.0.2)
+    mocha (3.0.2)
       ruby2_keywords (>= 0.0.5)
     mutex_m (0.1.2)
-    nokogiri (1.18.9-arm64-darwin)
+    nokogiri (1.19.1-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.18.9-x86_64-linux-gnu)
+    nokogiri (1.19.1-x86_64-linux-gnu)
       racc (~> 1.4)
+    ostruct (0.6.3)
     parallel (1.24.0)
     parser (3.3.0.5)
       ast (~> 2.4.1)
       racc
     phonelib (0.8.7)
+    pp (0.6.3)
+      prettyprint
     prettier_print (1.2.0)
-    pry (0.14.2)
-      coderay (~> 1.1)
-      method_source (~> 1.0)
-    pry-byebug (3.10.1)
-      byebug (~> 11.0)
-      pry (>= 0.13, < 0.15)
+    prettyprint (0.2.0)
+    prism (1.9.0)
     psych (5.1.0)
       stringio
     racc (1.8.1)
@@ -81,7 +91,13 @@ GEM
     rake (13.0.6)
     rake-compiler (1.2.1)
       rake
+    rdoc (7.2.0)
+      erb
+      psych (>= 4.0.0)
+      tsort
     regexp_parser (2.9.0)
+    reline (0.6.3)
+      io-console (~> 0.5)
     rexml (3.2.8)
       strscan (>= 3.0.9)
     rubocop (1.62.1)
@@ -114,11 +130,12 @@ GEM
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)
     sorbet-runtime (0.5.10648)
-    stringio (3.1.0)
+    stringio (3.2.0)
     strscan (3.1.0)
     syntax_tree (5.3.0)
       prettier_print (>= 1.2.0)
     thor (1.2.1)
+    tsort (0.2.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     unicode-display_width (2.5.0)
@@ -130,11 +147,12 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
+  benchmark
+  debug
   minitest (~> 5.0)
   minitest-focus
   minitest-reporters
   mocha
-  pry-byebug
   rake (~> 13.0)
   rake-compiler
   rubocop
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 0b85f23e1..a54719187 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -8,7 +8,7 @@
 require "minitest/reporters"
 require "minitest/focus" unless ENV["CI"]
 require "mocha/minitest"
-require "pry-byebug"
+require "debug"
 
 # All the locales used in the tests
 I18n.available_locales = Worldwide::Locales.known
diff --git a/worldwide.gemspec b/worldwide.gemspec
index 2e337985e..fa6c9d55c 100644
--- a/worldwide.gemspec
+++ b/worldwide.gemspec
@@ -28,5 +28,7 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency("activesupport", ">= 7.0")
   spec.add_dependency("i18n")
+  spec.add_dependency("logger")
+  spec.add_dependency("ostruct")
   spec.add_dependency("phonelib", "~> 0.8")
 end