Why is UInt64.max limited to 9223372036854775807?

Where do you get this ?

I tried in playground:

print(UInt64.max)

and got

18446744073709551615

I could also assign the value

let xMax : UInt64 = 18446744073709551615

But, of course, it is different with Int64

print(Int64.max)

gets

9223372036854775807

and assigning

let yMax : Int64 = 18446744073709551615

results in an error

error: integer literal '18446744073709551615' overflows when stored into 'Int64'

Because in that case, it has to range from negative to positive:

from -9223372036854775808 to +9223372036854775807 (from -263 to +263-1)

Yes, the error occurs in my playground:

It seems the value of max is correct but the playground sideview is showing an incorrect value.