They are actively working on the FreeBSD kernel, see Drew's post that I linked to (they did enough work to fill 100Gbit/sec pipe with 100,000 TCP connections.

They are actively working on the FreeBSD kernel, see Drew's post that I linked to (they did enough work to fill 100Gbit/sec pipe with 100,000 TCP connections. Impressive stuff). FreeBSD is used because they can get their work into the kernel, Linux is harder to change. The Linux use appears to me to just be VMs in AWS, it's just a service.