If you're moving those kind of speeds you're probably not doing packet filtering in software.
I use VPP and handle bonded speeds of 200gbit. Not that far fetched to also do this at 1000gbit.
Probably? But if you are then you’re certainly not using OpenBSD.
But you may be using Unix-y software to manage the interfaces and do offload programming:
* https://en.wikipedia.org/wiki/Vector_Packet_Processing
* https://www.youtube.com/watch?v=ptm9h-Lf0gg ("VPP: A 1Tbps+ router with a single IPv4 address")
* https://en.wikipedia.org/wiki/Cumulus_Networks