diff --git a/CHANGELOG.md b/CHANGELOG.md
index 985e8e30a..48f5840ea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,27 @@
-## Unreleased
+## 4.0.0. / 2024-01-19
 
-* _Your new feature here._
+* New: Add support for Rack 3 ([#1857])
+  * Note: you may want to read the [Rack 3 Upgrade Guide]
+
+* Require Ruby 2.7.8 as minimum Ruby version ([#1993])
+
+* Breaking change: Drop support for Rack 2 ([#1857])
+  * Note: when using Sinatra to start the web server, you now need the `rackup` gem installed
+
+* Breaking change: Remove the `IndifferentHash` initializer ([#1982])
+
+* Breaking change: Disable `session_hijacking` protection by default ([#1984])
+
+* Breaking change: Remove `Rack::Protection::EncryptedCookie` ([#1989])
+  * Note: cookies are still encrypted (by [`Rack::Session::Cookie`])
+
+[#1857]: https://github.com/sinatra/sinatra/pull/1857
+[#1993]: https://github.com/sinatra/sinatra/pull/1993
+[#1982]: https://github.com/sinatra/sinatra/pull/1982
+[#1984]: https://github.com/sinatra/sinatra/pull/1984
+[#1989]: https://github.com/sinatra/sinatra/pull/1989
+[`Rack::Session::Cookie`]: https://github.com/rack/rack-session
+[Rack 3 Upgrade Guide]: https://github.com/rack/rack/blob/main/UPGRADE-GUIDE.md
 
 ## 3.2.0 / 2023-12-29
 
diff --git a/VERSION b/VERSION
index 944880fa1..fcdb2e109 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-3.2.0
+4.0.0
diff --git a/lib/sinatra/version.rb b/lib/sinatra/version.rb
index 9a003cebb..f19f84897 100644
--- a/lib/sinatra/version.rb
+++ b/lib/sinatra/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Sinatra
-  VERSION = '3.2.0'
+  VERSION = '4.0.0'
 end
diff --git a/rack-protection/lib/rack/protection/version.rb b/rack-protection/lib/rack/protection/version.rb
index 41dffaa47..c2c2a74db 100644
--- a/rack-protection/lib/rack/protection/version.rb
+++ b/rack-protection/lib/rack/protection/version.rb
@@ -2,6 +2,6 @@
 
 module Rack
   module Protection
-    VERSION = '3.2.0'
+    VERSION = '4.0.0'
   end
 end
diff --git a/sinatra-contrib/lib/sinatra/contrib/version.rb b/sinatra-contrib/lib/sinatra/contrib/version.rb
index 18e6dfff5..a1218e746 100644
--- a/sinatra-contrib/lib/sinatra/contrib/version.rb
+++ b/sinatra-contrib/lib/sinatra/contrib/version.rb
@@ -2,6 +2,6 @@
 
 module Sinatra
   module Contrib
-    VERSION = '3.2.0'
+    VERSION = '4.0.0'
   end
 end