In rDSTO1e974580ac3c, @zack wrote:

Software source code objects---e.g., individual source code files, tarballs, commits, tagged releases, etc.---are stored in the Software Heritage (SWH) Archive in fully deduplicated form. That allows direct access to individual artifacts but require some preparation, usually in the form of collecting and assemblying multiple artifacts in a single bundle, when fast access to a set of related artifacts (e.g., the snapshot of a VCS repository, the archive corresponding to a Git commit, or a specific software release as a zip archive) is required.

The Software Heritage Vault is a cache of pre-built source code bundles which are assembled opportunistically retrieving objects from the Software Heritage Archive, can be accessed efficiently, and might be garbage collected after a long period of non use.