Not up to date with Composer 2 yet? Check the alpha1 changelog and alpha2 changelog, alpha3 changelog and RC1 changelog and especially the UPGRADE guide first.

Try it out now and get ready for the upcoming stable release

• Use composer self-update --preview to try the latest RC version (2.x).
• Use composer self-update --snapshot to try the latest dev build (2.x).
• Use composer self-update --stable to go back to stable releases (1.x for now).
• Use composer self-update --1 in CI/scripts if you want to pin Composer to 1.x until you are ready to migrate, this will ensure you stay on 1.x releases even once a 2.0 stable comes out.

Future timeline

Between RC1 and RC2 we only had to do a few fixes and mostly added a couple things to help plugin authors do their job more easily. This means 2.0 is already quite stable and we see it used in the wild quite a bit. The current plan is to release a 2.0 final before end of October. It is almost 100% compatible with Composer 1 with the exception of plugins, so please do try it ASAP and report any regression you find. The lock files from v1 can be used by v2 and vice-versa, so don't worry about that.

Changelog

• Breaking: Removed OperationInterface::getReason as the data was not accurate
• Added automatic removal of packages which are not required anymore whenever an update is done, this will purge packages previously left over by partial updates and require/remove
• Added shorthand aliases -w for --with-dependencies and -W for --with-all-dependencies on update/require/remove commands
• Added COMPOSER_DEBUG_EVENTS=1 env var support for plugin authors to figure out which events are triggered when
• Added setCustomCacheKey to PreFileDownloadEvent and fixed a cache bug for integrations changing the processed url of package archives
• Added Composer\Util\SyncHelper for plugin authors to deal with async Promises more easily
• Added $composer->getLoop()->getHttpDownloader() to get access to the main HttpDownloader instance in plugins
• Added a non-zero exit code (2) and warning to remove command when a package to be removed could not be removed
• Added --apcu-autoloader-prefix (or --apcu-prefix for dump-autoload command) flag to let people use apcu autoloading in a deterministic output way if that is needed
• Fixed version guesser to look at remote branches as well as local ones
• Lots of minor bug fixes and improvements