When you create a new Swift Package in Xcode 16, the Package.swift contents will look a bit like this:
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You might not be ready to use Swift 6.0 in your new packages yet. In those cases you can either set the Swift tools version back to 5.10 if you're not using any features from the 6.0 toolchain anyway or you can set your package's language mode to Swift 5 while keeping the 6.0 toolchain:
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