And NIST has a dashboard of adoption: https://usgv6-deploymon.antd.nist.gov/cgi-bin/generate-gov
Disclaimer: Not USDS/18F, just tech professional.
It appears a lot of .gov sites already support IPv6 but I was wondering if it's an official policy or just at the discretion of the tech team.
And NIST has a dashboard of adoption: https://usgv6-deploymon.antd.nist.gov/cgi-bin/generate-gov