They probably use feature detection. Cloudflare does.

arcanemachiner · on March 14, 2023

They probably don't. This user agent allows me to use the service on Firefox:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36 Edg/110.0.1587.69

throw10920 · on March 15, 2023

This will only work until and unless BingGPT becomes very popular, in which case Microsoft will very quickly implement better technical checks to try to anticompetitively boost Edge's market share.

cubefox · on March 15, 2023

Unrelated, but this user agent is so funny. I think the Chrome one is similar in claiming to be a lot of things it isn't.