Hey, thanks for your answer. While I get the two points, I think UserDefaults does not have user info dictonaries. I get that custom subclasses can be problematic, but up to my knowledge, if an open class would be marked Sendable and someone tried to subclass it, swift would emit a warning that the subclass must also be Sendable. Also, certain other classes in Foundation (like NumberFormatter) are Sendable, despite being open. In my particular case I cannot use the static UserDefaults.standard as I need to share the defaults within my app group. Potential code snippet could be: public final class Defaults: Sendable { private let defaults: UserDefaults public init( _ defaults: UserDefaults = UserDefaults(suiteName: "foobar") ?? .standard ) { self.defaults = defaults } I know I could in theory just pass the suite name and make UserDefaults computed (btw, is UserDefaults.standard also computed?), however I still don't get why UserDefaults is not sendable despite the docs mentioning its thread safe.

I've also filed a radar: FB10224177