Does arc4random on iOS use AES instead of RC4?

In general the API descriptions in macOS man pages also apply to iOS. So, for example, when the arc4random man page says:

These functions use a cryptographic pseudo-random number generator to
generate high quality random bytes very quickly.

that’s the semantics you should expect. How this is actually implemented is up to Apple. As it says at the bottom of that same man page:

it may be replaced again in the future as cryptographic techniques
advance

I also think it’s reasonable to assume that this:

The subsystem is re-seeded from the kernel random number subsystem on
a regular basis

ties into the ultimate source of randomness discussed in Apple Platform Security > Random number generation.

Finally, the getentropy man page makes for interesting reading.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Thanks Quinn! The Random Unification Swift evolution proposal makes the same assumption. Without a definitive source one could also assume that arc4random always utilizes RC4 and conclude that it (and thus the Swift SystemRandomNumberGenerator) is to be avoided, though.