vercel-build-speedlisted

# Vercel Build Speed (Next.js App Router) Derived from taking a real production Next.js 16 / Turbopack app from **7m21s to 3m46s**, measured per-phase on Vercel at every step. The single most useful lesson was epistemic: **the obvious lever was the wrong one.** Removing ~560MB of assets bought about 5 seconds. Cutting prerendered page count bought ~50. ## Calibration — this is one case study, not a benchmark Every number here comes from **one app, one Vercel plan, one 4-core / 8GB build machine**, in mid-2026 on Next 16.2. The app was a localized content site: four locales, ~2500 prerendered pages, a large `public/`, a 1.5GB git history. Weight the findings accordingly: **Likely to generalize** — the method (read the phase table, change one class of thing per deploy, re-attribute after each), the `vercel.json` failure mode, the Turbopack dead-config audit, and the *shape* of the ranking: compute and page count beat bytes. **Re-measure for your project** — every specific duration, and especially the three "myths". "Clone time is not proportional to tree size" and "Deploying outputs has a fixed floor" each rest on **two observations on one project**. They may be artifacts of this repo's history size or this plan's build infrastructure. If your `public/` dominates a small output, or your history is shallow, you may see the opposite. Do not skip a change because this document says the lever is weak — measure it. **Has a shelf life** — Turbopack and the Next config surface m