They’ve been doing it for years. I don’t remember how we first knew, but I know they’ve been using Swift in kernels for at least some of the other chips like the Secure Enclave or whatever.
I’m not sure exactly which. I assume it’s some of the code and not all. But it’s not new in the abstract.
That said I don’t think I’ve heard of it in the kernel of MacOS on the main processor. That may be new.
Either way this is certainly the most concrete announcement I remember them ever giving on this stuff.
I know internally they use an IPsec implementation written by Rust (I think in the iCloud infra). Heard this from an ex-Apple engineer Ben (forgot his last name) that did a wonderful presentation of Rust from first principles. He said that it was hard to get people in on Rust when most would argue for Swift.
Edit: This is the guy: https://rustcurious.com/course/
Some stuff was discussed at Meet with Apple security event a few months ago, and the talks on FoundationDB rewrite, or why Swift Embedded subset came to be.
However I miss them actually having had one of those 15 - 30m WWDC sessions, where they could have gone a bit deeper into the keynote examples