diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ba0824..c768ac7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,13 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This file follows the convention described at
 [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
+## [6.0.0] - 2023-06-19
+### Changed
+- Now requires Dart SDK version 3 or higher.
+- **BREAKING CHANGE**: Both `Option` and `Result` are now `sealed` classes
+  which allows for the use of exhaustive pattern matching.
+- feelsantiago: introduced the `sealed` class change to `Option` and `Result`.
+
 ## [5.3.0] - 2023-01-13
 ### Fixed
 - stumblinbear: Fix possible invalid casting in catch block.
diff --git a/pubspec.yaml b/pubspec.yaml
index d01ea8c..ecff6c5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,12 +1,12 @@
 name: oxidized
 description: Definitions of Rust-like types, Option and Result, to promote safer programming.
-version: 5.3.0
+version: 6.0.0
 homepage: https://github.com/nlfiedler/oxidized
 repository: https://github.com/nlfiedler/oxidized.git
 issue_tracker: https://github.com/nlfiedler/oxidized/issues
 
 environment:
-  sdk: ">=3.0.0"
+  sdk: ">=3.0.0 <4.0.0"
 
 dependencies:
   equatable: ^2.0.3