@vercel/flags-core@1.4.0 imports @vercel/flags-definitions, which is not on the npm registry — error on `next build`

[MaybeThisIsRu]

Summary

@vercel/flags-core@1.4.0 (pulled in transitively by @flags-sdk/vercel@1.3.0) contains compiled code that imports @vercel/flags-definitions. That package is not declared in @vercel/flags-core's dependencies and is not published to
the npm registry. As a result, any project using @flags-sdk/vercel fails next build with Module not found: Can't resolve '@vercel/flags-definitions'.

Local next dev does not surface the issue because dev mode compiles routes lazily and skips a full module-resolution sweep. Production builds (and Vercel deploys) hit it immediately.

Reproduction

Standard Vercel Flags setup, following https://vercel.com/docs/flags/vercel-flags/sdks/flags-sdk verbatim.

Flag definition — src/flags/my_flag.ts:

import { flag } from 'flags/next'
import { vercelAdapter } from '@flags-sdk/vercel'

type Entities = {
  userId: string
}

const identify = async (): Promise<Entities | null> => null

export const myFlag = flag<boolean, Entities>({
  key: 'my_flag',
  description: 'Example boolean feature flag',
  defaultValue: false,
  identify,
  adapter: vercelAdapter(),
})

Flags Discovery Endpoint — src/app/.well-known/vercel/flags/route.ts:

import { createFlagsDiscoveryEndpoint, getProviderData } from 'flags/next'
import * as flags from 'src/flags'

export const GET = createFlagsDiscoveryEndpoint(async () => getProviderData(flags))

Build: next build (also fails on every Vercel deploy).

Actual error

Module not found: Can't resolve '@vercel/flags-definitions' in '/path/to/node_modules/@vercel/flags-core/dist'

Import trace for requested module:
./node_modules/@vercel/flags-core/dist/chunk-OABKRAPP.js
./node_modules/@vercel/flags-core/dist/index.default.js
./node_modules/@flags-sdk/vercel/dist/index.js
./src/flags/my_flag.ts
./src/flags/index.ts
./src/app/.well-known/vercel/flags/route.ts

Verification that the package is missing

• npm view @vercel/flags-definitions returns 404 Not Found from registry.npmjs.org.
• node_modules/@vercel/flags-core/package.json declares only @vercel/functions, jose, and js-xxhash in dependencies. Its peerDependencies are @openfeature/server-sdk (optional) and next (optional). @vercel/flags-definitions is not
  referenced anywhere in the manifest.
• Grepping node_modules/@vercel/flags-core/dist/chunk-OABKRAPP.js confirms a literal "@vercel/flags-definitions" import string is present in the compiled bundle.

Expected behavior

@vercel/flags-core@1.4.0 should build cleanly when consumed via the canonical Vercel Flags setup. Either:

1. Publish @vercel/flags-definitions to npm and declare it in @vercel/flags-core's dependencies, or
2. Re-bundle @vercel/flags-core so the import to @vercel/flags-definitions is inlined or removed.

Environment

	Version
Next.js	15.4.10
flags	4.0.6
@flags-sdk/vercel	1.3.0
@vercel/flags-core (resolved transitively)	1.4.0
@vercel/toolbar	0.2.5
Node	v22.19.0
Package manager	Yarn 1.22.22

[MaybeThisIsRu]

Someone has shimmed this

• https://github.com/Aadvait-Hirde/KTP-Indiana/blob/main/next.config.ts
• https://github.com/Aadvait-Hirde/KTP-Indiana/blob/main/lib/vercel-flags-definitions-shim.ts

I suppose a non-critical error, but should be documented somewhere!

[dferber90]

Do you have a repro where the build is actually failing? It is expected that @vercel/flags-definitions is not published and may not exist. We generate this package at build time when building on Vercel to embed fallback definitions.

It should fail silently if you are building outside of Vercel. Please let me know if this is not the case.

https://vercel.com/docs/flags/vercel-flags/sdks/core#embedded-definitions