Will Swift Concurrency deploy back to older OSs?

I want to thank everyone for their impassioned feedback on this thread. I hope everyone feels heard. I, and everyone else who works on Swift, recognize the immense value of Swift concurrency working on earlier OS releases. I'll reiterate again that backward deployment is something we're exploring. That's not a token statement to throw to a group of disappointed people, but a genuine statement of intent. That's not a promise that we can even deliver backward deployment, but we will look into it.

We understand that requiring the latest OS limits the adoption of language features. In general, we try very hard for language features to have maximum availability. But sometimes this is not easy to do. In the case of Swift concurrency, some of the runtime support being alluded to relates to changes to Dispatch to support Swift concurrency. Dispatch is plumbed through both userspace and the kernel, and those changes were important to meet performance (and in some areas, correctness) goals to support Swift concurrency in code that makes heavy use of it.

You have all been heard, and your candid feedback is appreciated. I'm not really sure if there is more that I can say at this point to acknowledge the concerns and points raised. I recognize that many of you feel Swift concurrency remains a far off thing that you cannot consider using for some time because of the requirement on iOS 15. The possibility of backward deployment will be explored — but as I said I cannot promise an outcome at this moment. While many of you may be sour about this, I do ask that you all continue to look at Swift concurrency in some way, as it is still taking full shape and will continue to evolve with community discussion on the road to Swift 6.