Some Open DNS operators provide a way to return the IP address of the request packet.
ds stands for dual stack. It is also reachable under
whoami.ipv6.akahelp.net to force IPv6 or
whoami.ipv4.akahelp.net to force IPv4.
ns stands for the unicast IP address of the recursive resolver.
ecs contains the EDNS client subnet information if the resolver uses the option. In this case,
ip contains a representative IP within the ECS, not necessarily the IP of the client.
The new version is introduced in this blog post https://www.akamai.com/blog/developers/introducing-new-whoami-tool-dns-resolver-information.
The old version might be decommissioned: