npm warn Unknown env config "cache-dir" caused by Vercel build environment

Since October 15, 2026, every deployment of my Next.js project shows the following warning twice:

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npm warn Unknown env config "cache-dir". This will stop working in the next major version of npm.

I verified that this does not come from my project or local npm configuration:

• no project .npmrc
• user .npmrc contains only commented defaults
• global npm .npmrc is empty
• npm config list does not contain cache-dir
• no NPM_CONFIG_CACHE_DIR or other cache-related environment variable is configured in the Vercel project
• no relevant environment variable exists locally
• package.json and package-lock.json did not change between the last deployment without the warning (October 10) and the first deployment with the warning (October 15)

I then temporarily used a custom Vercel Install Command to print all npm_config_* environment variables.

The Vercel build output showed:

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npm_config_cache_dir = /vercel/path0/.vercel/cache/pnpm
2
pnpm_config_cache_dir = /vercel/path0/.vercel/cache/pnpm
3
11.20.0
4
npm warn Unknown env config "cache-dir".

The warning appears once during dependency installation and again when Vercel runs:

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npm run build

So npm_config_cache_dir appears to be injected by the Vercel build environment itself. npm 11.20.0 interprets this as the unsupported configuration key cache-dir.

The deployment itself succeeds; this is currently only a warning.

Could Vercel please check whether npm_config_cache_dir should still be injected into npm builds, or whether this should use a supported npm cache configuration instead?