The described technology is directed towards maintaining and using a version-based hierarchy of software resources (e.g., file system files) to return version-specific responses to clients. A client sends its version information with each data request, and gets back a response based upon that version. Version changes are made by maintaining the current version of each software code resource and overriding the current version with a previous version for clients as needed. The technology allows updates (e.g., for new devices and new software resource versions) to be supported by inserting resources into the resource hierarchy and moving resources therein based upon versioning. A system based on deltas is also contemplated, in which only parts of a file may be changed relative to a different version, instead of overriding the entire file.