ipinfo.io's API and site is dualstack. But for IPv6 connection, you need to use v6.ipinfo.io for the API service.

Even though nobody asked, I have to mention this every time there is a discussion about IPv6 and IP address data. According to domain name records, even if a site supports both IPv4 and IPv6 it defaults to IPv6. I would love to know why.

I have come across a lot of people saying IPinfo doesn't support IPv6. The internet as an ecosystem doesn't completely support IPv6, but we do. So, mentioning it constantly in every discussion is my current approach.