At least on the stock MacOS awk, you can get up to 2^53 before arithmetic breaks (doesn't wrap, just doesn't go up any more which means the one-liner still works.)
> echo '2^53-1' | bc 9007199254740991 > seq 1 10 | awk 'BEGIN{a[123]=9007199254740991;b=a[123]}{a[123]++}END{print a[123],b,a[123]-b}' 9007199254740992 9007199254740991 1
At least on the stock MacOS awk, you can get up to 2^53 before arithmetic breaks (doesn't wrap, just doesn't go up any more which means the one-liner still works.)
Even with one character per line, you'd need an 18PB file before you got to this limit, afaict.