The Ionic CLI is made up of several packages, all of which have individual CHANGELOG files. Changes made in one (especially @ionic/cli-utils) may affect the other, but in general you can expect changes relating to Cordova to be made in @ionic/cli-plugin-cordova, etc.

Global:

• ionic (CHANGELOG.md): The CLI executable.
• @ionic/cli-utils (CHANGELOG.md): The CLI utilities library.
• @ionic/cli-plugin-proxy (CHANGELOG.md): The plugin for proxying CLI requests through a firewall.

Local (per project):

• @ionic/cli-plugin-cordova (CHANGELOG.md): The plugin for Cordova integration. Essential for an Ionic/Cordova app.
• @ionic/cli-plugin-ionic-angular (CHANGELOG.md): The project plugin for Ionic Angular projects. Provides useful build tools and generators.
• @ionic/cli-plugin-ionic1 (CHANGELOG.md): The project plugin for Ionic 1 that has functionality ported from the legacy CLI.

CLI v3 Blog Post 🎉

• If you're using Ionic Deploy, you'll need to update ionic-plugin-deploy to the latest version. See #2237 and ionic-team/ionic-plugin-deploy#122.

• setup: This was only used to setup sass in Ionic 1 projects, which now is now handled in start.
• share: Please use the Dashboard to manage collaborators.
• lib, add, remove, list: For v1 projects, we recommend using bower.
• io: Please configure apps in the Dashboard and use link to associate your local project.
• security: Please manage security profiles in the Dashboard.
• push: Please manage push credentials (through security profiles) in the Dashboard.
• config: Please manually edit the ionic.config.json file.
• service: Please migrate your app to use the Ionic Cloud Client.
• state: The plugins and platforms can be managed entirely by Cordova. Please remove the cordovaPlatforms and cordovaPlugins keys from your package.json file. If you're using Cordova 7, please review the announcement about how Cordova uses config.xml and package.json to manage plugins and platforms.

• Added commands: signup. Signup will change in the future, but as for now it simply opens up the signup page.
• Cordova commands have been namespaced to allow for future platform support and to reduce clutter. Additionally, Cordova functionality has been moved into a CLI plugin, which is installed by default with new Ionic projects and can be installed in existing Ionic projects with npm i --save @ionic/cli-plugin-cordova.
• Many command arguments, options, and flags have changed. For example, the --v1 and --v2 flags in ionic start have been removed in favor of --type with respective values ionic1 (for v1) and ionic-angular (for latest Ionic Angular version). Please use ionic help <commands> for new command usage.
• generate command has been overhauled to interactively generate components, pages, directives, etc. It uses the power of app-scripts to hook up generated entities to your app. In the future, generators will continue to be expanded upon.

Older changes (CLI 2 and before) can be viewed in the 2.x branch's CHANGELOG.md.