The lack of Apple documentation on ExtensionFoundation (and ExtensionKit) is almost funny. What can it do? What can it not do? The sum of all knowledge is: “try it and find out”.
I’ve made it as far as: myProcess = try await AppExtensionProcess(configuration: myConfig), which doesn’t cause an error and returns… but not a single line in the extension code is executed.
It’s running! Not working as intended, of course, but at least running.
Thousands of thanks to @khaost who has the only working example of iOS extensions (that I could find): https://github.com/KhaosT/UIExtensionExample
GitHub - KhaosT/UIExtensionExample: ExtensionKit demo for iOS 26

ExtensionKit demo for iOS 26. Contribute to KhaosT/UIExtensionExample development by creating an account on GitHub.

GitHub
@nholzschuch Yeah the lack of documentation is wild. What are the issues you're running into?
@khaost Right now I have trouble uploading to the AppStore (“The value of the EXExtensionPointIdentifier key, AsheKube.app.a-Shell.localWebServer, in the Info.plist of “a-Shell.app/Extensions/localWebServer.appex” is invalid.”), and debugging works once in a while, but more importantly it seems that I cannot run a web server in an extension: communications with the outside are really limited to the XPC connection.
That’s disappointing, but now that I have it running, I have other possible uses.
@nholzschuch Very curious about your findings, I was also hoping I could use extensions for something when they were added to iOS, but didn't get a chance to play with them yet
@alexstaravoitau Thanks! So far:
- the web server runs, but doesn’t receive the requests (so it’s useless as a web server).
- they’re limited to 30 MB (not tested by me but reported elsewhere).
- it seems to be running as a separate process, with a different pid.
- if the extension calls exit(), it ends the process (but not the enclosing app).
- still unable to upload to the AppStore.
@alexstaravoitau I actually got an answer on the developer forums: "ah, we didn't envision developers using extensions within their own iOS apps. Interesting. Please file bug report."
@nholzschuch Ah very interesting! And I suppose explains some of the limitations.