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vercel multi-service builds support experimental concurrency

Introduced 2026-08-29 · score 0.94

HOW TO USE IT

For a multi-service project, set `VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY` above `1` to run fork-eligible service builds concurrently; builds are grouped by install scope. The release note allows an integer, a percentage of available parallelism, or `auto`.

VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY=2 vercel build
VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY=50% vercel build
VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY=auto vercel build

WHY THIS HELPS

Build a project with multiple services and control how many eligible service builds run concurrently.

BEFORE THIS CHANGE

Set `VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY` to its default value of 1 for fully sequential service builds.

REQUIREMENTS AND LIMITATIONS

  • Version: 59.10.0
  • Availability: Experimental; concurrency values above 1 enable parallel builds.
  • VERCEL_EXPERIMENTAL_BUILD_CONCURRENCY: Concurrency setting: integer, percentage of available parallelism, or `auto`; default `1` preserves sequential behavior.
  • The default of 1 preserves fully sequential behavior.
  • Only fork-eligible service builds run concurrently.
  • Builds are grouped by install scope so package-manager installs never race.

FIRST-PARTY EVIDENCE

Check the installed version and the source before using it. Entry JSON

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