[gkolli]

The startup Physical Intelligence has a domain of π.com, which redirects to/from https://www.xn--1xa.com

How is this character represented in the domain name?

[Zambyte]

Check out https://en.wikipedia.org/wiki/Internationalized_domain_name

In short, it's not a redirect, it's an ASCII encoding for representing Unicode text called Punycode: https://en.wikipedia.org/wiki/Punycode