Next.js API routes vs route handlers is one of those migrations that looks trivial in the docs but bites you on caching semantics and runtime defaults. Both surface HTTP endpoints inside a Next.js project, but they sit in fundamentally different mental models — one is a Node.js request/response wrapper, the other is built on the Web Fetch API and plays by App Router rules. What each one actually is Pages Router API routes live at pages/api/**/*.ts . They receive a NextApiReques...