Julia’s default sorting is not a simple algorithm but a rather complex pipeline thanks to awesome work by @Lilith
I highly recommend checking out her JuliaCon 2023 talk about the full sorting pipeline https://www.youtube.com/watch?v=dXkNazmV9pA.
For reference this is what it looks like in my Julia 1.10.2 and if you look closely there is a RadixSort in there for a suitable case:
julia> Base.Sort.DEFAULT_STABLE
Base.Sort.MissingOptimization(
Base.Sort.BoolOptimization(
Base.Sort.Small{10}(
Base.Sort.InsertionSortAlg(),
Base.Sort.IEEEFloatOptimization(
Base.Sort.IsUIntMappable(
Base.Sort.Small{40}(
Base.Sort.InsertionSortAlg(),
Base.Sort.CheckSorted(
Base.Sort.ComputeExtrema(
Base.Sort.ConsiderCountingSort(
Base.Sort.CountingSort(),
Base.Sort.ConsiderRadixSort(
Base.Sort.RadixSort(),
Base.Sort.Small{80}(
Base.Sort.InsertionSortAlg(),
Base.Sort.ScratchQuickSort(missing, missing,
Base.Sort.InsertionSortAlg()))))))),
Base.Sort.StableCheckSorted(
Base.Sort.ScratchQuickSort(missing, missing,
Base.Sort.InsertionSortAlg())))))))