https://radar.cloudflare.com/domains
Source of this is from Matthew Prince, Co-founder & CEO of Cloudflare posted at 11:34 Jul 9,2023. It was posted to his twitter (@eastdakota). Not linking to twitter bc don’t want a deadlink next time twitter makes API changes. And not to drive traffic to twitter :D
Edit: July 11th update, arstechnica published a detailed explanation
see comment above, but in short twitter need not hire cloudflare for services. Cloudflare plays an important role in the backbone of the internet. If twitter is resolved through cloudflare’s DNS, cloudflare can estimate the volume of traffic to Twitter.com