Yes — api.census.gov has IPv6.

Has both IPv4 (A) and IPv6 (AAAA) addresses.

B
IPv6 readiness
Works over IPv6, with one gap: www doesn't fully work over IPv6.
Website over IPv6
api.census.gov has an AAAA record and answers on it.
✓ 2610:20:2010:a05:1000:0:9481:4bbf answers · 443
yes
www over IPv6
www.api.census.gov has no AAAA record.		no
Mail servers (MX) have IPv6
No MX records, so mail goes to the domain's own address (implicit MX). It has an AAAA record.		yes
Nameservers have IPv6
3 of 3 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.
gold.foundationdns.com ✓gold.foundationdns.net ✓gold.foundationdns.org ✓
yes
HTTPS over IPv6 · not part of the grade yet
Loads over IPv6 with a valid certificate after 1 redirect: HTTP 200.
https://api.census.gov/ via 2610:20:2010:a05:1000:0:9481:4bbf → 302https://www.census.gov/data/developers.html via 2606:4700:78::90:0:183 → 200
works
 Load api.census.gov over IPv6 from up to six other places — a second opinion.

What's keeping api.census.gov from an A

  1. Add IPv6 for www.api.census.gov
    www.api.census.gov has no AAAA record. Get www's IPv6 address from whoever hosts www and add it as an AAAA record. If the same server already serves both names (and its certificate covers www), you can reuse api.census.gov's AAAA record(s) for www. How to add an AAAA record

Check again

api.census.gov  Has IPv6

A (IPv4)148.129.75.191
AAAA (IPv6)2610:20:2010:a05:1000:0:9481:4bbf

www.api.census.gov  No address

A (IPv4)none
AAAA (IPv6)none

Browsers on dual-stack networks will usually pick IPv6 here (the "Happy Eyeballs" algorithm races both and prefers v6).

Copy the evidence — a citation-ready record of this measurement

 Permanent link: aaaa.bot/r/VKSklCQSuk · How we measure

Checked 2026-11-01 23:47:42 UTC. Full DNS report: dns.pizza/domain/api.census.gov · JSON: /api/v1/api.census.gov