diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index f3d396a..5c14dba 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -14,7 +14,7 @@ env:
   #
   # If updating this value, you probably also want to add a new version to the
   # spec version matrix below.
-  RUBY_VERSION: "3.4"
+  RUBY_VERSION: "4.0"
 
   # A suitable URL for a test database.
   TEST_DATABASE_NAME: river_test
@@ -134,6 +134,7 @@ jobs:
           - "3.2"
           - "3.3"
           - "3.4"
+          - "4.0"
 
     services:
       postgres:
diff --git a/.tool-versions b/.tool-versions
index 380cf51..b77860b 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -1 +1 @@
-ruby 3.4
+ruby 4.0
diff --git a/Gemfile b/Gemfile
index d174c52..ab665f6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,6 +3,10 @@ source "https://rubygems.org"
 gemspec
 
 group :development, :test do
+  # both gems temporarily pointed to master to get Ruby 4.0 support
+  #gem "ffi", git: "https://github.com/ffi/ffi", submodules: true
+  #gem "pg", git: "https://github.com/ged/ruby-pg", force_ruby_platform: true
+
   gem "standard"
   gem "steep"
 end
diff --git a/Gemfile.lock b/Gemfile.lock
index 772389f..5fce7f4 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -13,14 +13,14 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (8.0.3)
+    activesupport (8.1.1)
       base64
-      benchmark (>= 0.3)
       bigdecimal
       concurrent-ruby (~> 1.0, >= 1.3.1)
       connection_pool (>= 2.2.5)
       drb
       i18n (>= 1.6, < 2)
+      json
       logger (>= 1.4.2)
       minitest (>= 5.1)
       securerandom (>= 0.3)
@@ -28,49 +28,48 @@ GEM
       uri (>= 0.13.1)
     ast (2.4.3)
     base64 (0.3.0)
-    benchmark (0.4.1)
-    bigdecimal (3.3.1)
-    concurrent-ruby (1.3.5)
-    connection_pool (2.5.4)
+    bigdecimal (4.0.1)
+    concurrent-ruby (1.3.6)
+    connection_pool (3.0.2)
     csv (3.3.5)
-    date (3.4.1)
-    debug (1.11.0)
+    date (3.5.1)
+    debug (1.11.1)
       irb (~> 1.10)
       reline (>= 0.3.8)
     diff-lcs (1.6.2)
     docile (1.4.1)
     drb (2.2.3)
-    erb (5.1.1)
-    ffi (1.17.2-arm64-darwin)
-    ffi (1.17.2-x86_64-linux-gnu)
-    fileutils (1.7.3)
-    i18n (1.14.7)
+    erb (6.0.1)
+    ffi (1.17.2)
+    fileutils (1.8.0)
+    i18n (1.14.8)
       concurrent-ruby (~> 1.0)
-    io-console (0.8.1)
-    irb (1.15.2)
+    io-console (0.8.2)
+    irb (1.16.0)
       pp (>= 0.6.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
-    json (2.15.1)
+    json (2.18.0)
     language_server-protocol (3.17.0.5)
     lint_roller (1.1.0)
     listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     logger (1.7.0)
-    minitest (5.26.0)
+    minitest (6.0.0)
+      prism (~> 1.5)
     mutex_m (0.3.0)
     parallel (1.27.0)
-    parser (3.3.9.0)
+    parser (3.3.10.0)
       ast (~> 2.4.1)
       racc
-    pg (1.6.2-arm64-darwin)
+    pg (1.6.2)
     pg (1.6.2-x86_64-linux)
     pp (0.6.3)
       prettyprint
     prettyprint (0.2.0)
-    prism (1.6.0)
-    psych (5.2.6)
+    prism (1.7.0)
+    psych (5.3.1)
       date
       stringio
     racc (1.8.1)
@@ -78,14 +77,14 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rbs (3.9.5)
+    rbs (3.10.0)
       logger
-    rdoc (6.15.0)
+    rdoc (7.0.3)
       erb
       psych (>= 4.0.0)
       tsort
     regexp_parser (2.11.3)
-    reline (0.6.2)
+    reline (0.6.3)
       io-console (~> 0.5)
     rspec-core (3.13.6)
       rspec-support (~> 3.13.0)
@@ -93,7 +92,7 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
     rspec-support (3.13.6)
-    rubocop (1.80.2)
+    rubocop (1.81.7)
       json (~> 2.3)
       language_server-protocol (~> 3.17.0.2)
       lint_roller (~> 1.1.0)
@@ -101,19 +100,19 @@ GEM
       parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 2.9.3, < 3.0)
-      rubocop-ast (>= 1.46.0, < 2.0)
+      rubocop-ast (>= 1.47.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 2.4.0, < 4.0)
-    rubocop-ast (1.47.1)
+    rubocop-ast (1.48.0)
       parser (>= 3.3.7.2)
       prism (~> 1.4)
-    rubocop-performance (1.25.0)
+    rubocop-performance (1.26.1)
       lint_roller (~> 1.1)
       rubocop (>= 1.75.0, < 2.0)
-      rubocop-ast (>= 1.38.0, < 2.0)
+      rubocop-ast (>= 1.47.1, < 2.0)
     ruby-progressbar (1.13.0)
     securerandom (0.4.1)
-    sequel (5.97.0)
+    sequel (5.99.0)
       bigdecimal
     simplecov (0.22.0)
       docile (~> 1.1)
@@ -121,18 +120,18 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.13.2)
     simplecov_json_formatter (0.1.4)
-    standard (1.51.1)
+    standard (1.52.0)
       language_server-protocol (~> 3.17.0.2)
       lint_roller (~> 1.0)
-      rubocop (~> 1.80.2)
+      rubocop (~> 1.81.7)
       standard-custom (~> 1.0.0)
       standard-performance (~> 1.8)
     standard-custom (1.0.2)
       lint_roller (~> 1.0)
       rubocop (~> 1.50)
-    standard-performance (1.8.0)
+    standard-performance (1.9.0)
       lint_roller (~> 1.1)
-      rubocop-performance (~> 1.25.0)
+      rubocop-performance (~> 1.26.0)
     steep (1.10.0)
       activesupport (>= 5.1)
       concurrent-ruby (>= 1.1.10)
@@ -150,8 +149,8 @@ GEM
       strscan (>= 1.0.0)
       terminal-table (>= 2, < 5)
       uri (>= 0.12.0)
-    stringio (3.1.7)
-    strscan (3.1.5)
+    stringio (3.2.0)
+    strscan (3.1.6)
     terminal-table (4.0.0)
       unicode-display_width (>= 1.1.1, < 4)
     tsort (0.2.0)
@@ -159,8 +158,8 @@ GEM
       concurrent-ruby (~> 1.0)
     unicode-display_width (3.2.0)
       unicode-emoji (~> 4.1)
-    unicode-emoji (4.1.0)
-    uri (1.0.4)
+    unicode-emoji (4.2.0)
+    uri (1.1.1)
 
 PLATFORMS
   arm64-darwin-22
diff --git a/driver/riverqueue-activerecord/Gemfile.lock b/driver/riverqueue-activerecord/Gemfile.lock
index 6b7ee0e..7011a8b 100644
--- a/driver/riverqueue-activerecord/Gemfile.lock
+++ b/driver/riverqueue-activerecord/Gemfile.lock
@@ -56,12 +56,14 @@ GEM
     language_server-protocol (3.17.0.3)
     lint_roller (1.1.0)
     logger (1.6.4)
-    minitest (5.25.4)
+    minitest (6.0.0)
+      prism (~> 1.5)
     parallel (1.26.3)
     parser (3.3.6.0)
       ast (~> 2.4.1)
       racc
     pg (1.5.9)
+    prism (1.7.0)
     psych (5.2.2)
       date
       stringio
@@ -119,7 +121,7 @@ GEM
       concurrent-ruby (~> 1.0)
     unicode-display_width (3.1.2)
       unicode-emoji (~> 4.0, >= 4.0.4)
-    unicode-emoji (4.0.4)
+    unicode-emoji (4.2.0)
     uri (1.0.2)
 
 PLATFORMS
diff --git a/driver/riverqueue-sequel/Gemfile.lock b/driver/riverqueue-sequel/Gemfile.lock
index e3e30ff..bd9f0df 100644
--- a/driver/riverqueue-sequel/Gemfile.lock
+++ b/driver/riverqueue-sequel/Gemfile.lock
@@ -72,7 +72,7 @@ GEM
       rubocop-performance (~> 1.23.0)
     unicode-display_width (3.1.2)
       unicode-emoji (~> 4.0, >= 4.0.4)
-    unicode-emoji (4.0.4)
+    unicode-emoji (4.2.0)
 
 PLATFORMS
   arm64-darwin-22