Right on, Blaine Garrett . FTR I did exhaustive tests including NODE_ENV=development next start , NODE_ENV=production next dev , etc -- but I'm also currently stuck on v10.2.3. Maybe this has since changed in v11 or v12. IMHO Next.js made a rare misstep in being both opinionated and rigid about proper support for true 12-factor config that lives in the runtime deploy environment. It probably stems from their original desire to stay "close" to create-react-app, and ofc whatever most closely aligns with Vercel's preferred hosting model. (shrug) Slainte, Chris PS See also https://github.com/vercel/next.js/issues/12772#issuecomment-790228350 and https://github.com/vercel/next.js/discussions/25764

Hi Blaine Garrett , Thanks for sharing a great writeup about a gnarly topic. I have a minor correction to share. You wrote: "Note: This hierarchy optionally goes further with .env.development and .env.production (corresponding to the value of NODE_ENV)..." But they don't actually correspond to the value of NODE_ENV. Next.JS bases its decision to read from .env.development vs .env.production on one thing only: whether you start the app with next dev or next start . That's all. NODE_ENV's value is irrelevant to that bit of Next-specific logic. AFAICT you get the rest of the complicated picture right; hopefully my comment will inspire you to edit the post, or at least help ensure other readers aren't accidentally misled. Slainte, Chris