[drmpeg]

They're using frequencies in the 10.7 to 30.0 GHz range (GPS is much lower at 1.575 GHz) that are already allocated to satellite operations. However, they do have to share these frequencies with others. You can read all the frequency stipulations in the FCC authorization.

https://docs.fcc.gov/public/attachments/FCC-20-102A1.pdf

For example, operation at 27.5 to 28.35 GHz overlaps a 5G millimeter band in the US. 5G is primary and satellite uplink is secondary in that band, so if Kuiper interferes with a 5G installation, they can be ordered to mitigate the interference (possibly by stopping transmissions).