Currently string interpolation when all of the parts are strings prefers to lower to a string.Concat call when there's a string.Concat overload with the exact same number of string parameters. Beyond that, it falls back to using normal interpolation mechanisms. Now that in .NET 9 there's a string.Concat(params ReadOnlySpan<string>) overload, it'd be nice if string interpolation preferred to use that overload when it's available, when all the parts are strings, and when there isn't a better overload of string.Concat available. This statement is invalidated by the new params span overload, which can support passing in all of the strings without an allocation:

cc: @333fred