I think GP might’ve been referring to the part of Jeff’s post that references GPS, which I think may be a slight misunderstanding of the NIST email (saying “people using NIST + GPS for time transfer failed over to other sites” rather than “GPS failed over to another site”).
The GPS satellite clocks are steered to the US Naval Observatory’s UTC as opposed to NIST’s, and GPS fails over to the USNO’s Alternate Master Clock [0] in Colorado.
I find this stuff really interesting, so if anyone's curious, here's a few more tidbits:
GPS system time is currently 18s ahead of UTC since it doesn't take UTC's leap seconds into account [0]
This (old) paper from USNO [1] goes into more detail about how GPS time is related to USNO's realization of UTC, as well as talking a bit about how TAI is determined (in hindsight! - by collecting data from clocks around the world and then processing it).
The GPS satellite clocks are steered to the US Naval Observatory’s UTC as opposed to NIST’s, and GPS fails over to the USNO’s Alternate Master Clock [0] in Colorado.
[0] https://www.cnmoc.usff.navy.mil/Our-Commands/United-States-N...