Apex Code Versions

To aid backwards-compatibility, classes and triggers are stored with the version settings for a specific Salesforce API version. If an Apex class or trigger references components, such as a custom object, in installed managed packages, the version settings for each managed package referenced by the class are saved too. This ensures that as Apex, the API, and the components in managed packages evolve in subsequent released versions, a class or trigger is still bound to versions with specific, known behavior.

Setting a version for an installed package determines the exposed interface and behavior of any Apex code in the installed package. This allows you to continue to reference Apex that may be deprecated in the latest version of an installed package, if you installed a version of the package before the code was deprecated.

Typically, you reference the latest Salesforce API version and each installed package version. If you save an Apex class or trigger without specifying the Salesforce API version, the class or trigger is associated with the latest installed version by default. If you save an Apex class or trigger that references a managed package without specifying a version of the managed package, the class or trigger is associated with the latest installed version of the managed package by default.