(I work at Vercel) We are primarily built on AWS hardware and our own software.
For example, a custom CDN/proxy¹, build infrastructure², compute³, WAF⁴, etc. – and then take advantage of AWS' network/fiber (like AGA⁵) and their hardware.
¹: https://vercel.com/blog/life-of-a-vercel-request-what-happen...
²: https://vercel.com/blog/a-deep-dive-into-hive-vercels-builds...
³: https://vercel.com/blog/introducing-fluid-compute
⁴: https://vercel.com/blog/preventing-infrastructure-abuse-with...