Apex Versioning in Managed Packages

A package version is a number that identifies the set of components uploaded in a package. The version number has the format majorNumber.minorNumber.patchNumber (for example, 2.1.3). The major and minor numbers increase to a chosen value during every major release. The patchNumber is generated and updated only for a patch release.

Unmanaged packages aren’t upgradeable, so each package version is simply a set of components for distribution. A package version has more significance for managed packages. With managed packages, you can specify different component behavior based on the package version. This practice allows you to evolve the components in your managed package without breaking existing subscriber integrations.

When an existing subscriber installs a new package version, there’s still only one instance of each component in the package. However, the components can emulate older versions. For example, a subscriber can use a managed package that contains an Apex class. If the publisher decides to deprecate a method in the Apex class and release a new package version, the subscriber still sees only one instance of the Apex class after installing the new version. However, this Apex class can still emulate the previous version for any code that references the deprecated method in the older version.