This is a joint session with CWS, our client. Most "Sitecore on Vercel" talks are greenfield. CWS isn't: one public website fronts five sites across two Sitecore tenants, with a legacy CMSs still live for departments that haven't moved. We walk the routing that makes it work — source-then-locale resolution, legacy fallback, zero downtime — and the real scars: Edge propagation delay, protected-deployment revalidation, redirect loops. Leave able to cut over a multi-CMS estate one slice at a time.