As of this afternoon Bandwidth is now routing through Cloudflare Magic Transit for DDOS mitigation as you can see here. https://bgp.tools/prefix/67.231.12.0/24 and https://bgp.tools/prefix/216.82.224.0/24
This is the same service voip.ms used to mitigate the DDOS. Prior to that it would appear they were using Arbor DDOS Mitigation service through the NTT Fiber but it did not seem to be helping.