Comment by Cu3PO42

Any stretch of fibre you replace with hollow core fibre will see latency reduced to two thirds of what it was before. (It would be half if the speed of light in it were double what it is in normal fibre, but it's only 50% faster).

You say sans routing latencies, but these are very much significant for intercontinental communication:

I get 6ms ping to AWS eu-central, which is less than 100km by air from me. I get 114ms to AWS us-east-1, which is roughly 6500km. Now 6500km / (2/3 * c) = ~32ms. So if there were a fibre running in a straight line, time in the fibre would be 32ms. Of course it isn't running in a straight line, so let's say 50ms are pure "light traveling through fibre". Switching all of that to hollow-core would cut that to 33ms, so that's a savings of 17ms or roughly 15% of my total latency.

This is still a very nice savings, but very far off from cutting latency in half.

(Also, it's a single hop from my company network to DE-CIX, one of the largest internet exchanges in the world, so I feel confident saying my results aren't skewed by a bad uplink.)