Hello, I've already reported this issue via Feedback Assistant a month ago (FB22340897) but it's still open and I'd like to know whether I can expect something to be changed regarding it. Here are the details: It seems that Xcode 26.4 started specifying nonisolated for the resourceBundleDescription in the generated stringSymbols files for Swift packages: from: private let resourceBundleDescription = LocalizedStringResource.BundleDescription.atURL(resourceBundle.bundleURL) to: private nonisolated let resourceBundleDescription = LocalizedStringResource.BundleDescription.atURL(resourceBundle.bundleURL) This causes a compilation error: Main actor-isolated default value in a nonisolated context when the Package.swift for the Swift Package in which the string catalog is located specifies: swiftSettings: [.defaultIsolation(MainActor.self)] Since all tools (String Catalogs, Swift Packages and default actor isolation to be Main Actor) are recommended by Apple, I believe it should be possible to use all these together like before Xcode 26.4.