偶然发现 X 部分域名解析到了 Cloudflare CDN：

> nslookup t.co.cdn.cloudflare.net
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   t.co.cdn.cloudflare.net
Address: 162.159.140.229
Name:   t.co.cdn.cloudflare.net
Address: 172.66.0.227
Name:   t.co.cdn.cloudflare.net
Address: 2606:4700:7::e3
Name:   t.co.cdn.cloudflare.net
Address: 2a06:98c1:58::e3

> nslookup pbs.twimg.com.cdn.cloudflare.net
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   pbs.twimg.com.cdn.cloudflare.net
Address: 104.18.9.251
Name:   pbs.twimg.com.cdn.cloudflare.net
Address: 104.18.8.251
Name:   pbs.twimg.com.cdn.cloudflare.net
Address: 2606:4700::6812:8fb
Name:   pbs.twimg.com.cdn.cloudflare.net
Address: 2606:4700::6812:9fb

主域名 x.com 也有对应的 CNAME 接入，只是没有 AAAA 记录：

> nslookup x.com.cdn.cloudflare.net
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   x.com.cdn.cloudflare.net
Address: 172.66.0.227
Name:   x.com.cdn.cloudflare.net
Address: 162.159.140.229

手动把 x.com 解析过去 IPv6 地址，可以正常打开首页。不过好像没有什么实际用途。。