`experimental.cssChunking: "graph"` is only supported with T

Error message

`experimental.cssChunking: "graph"` is only supported with Turbopack. Please remove the option or run Next.js with Turbopack in ${configFileName}.

What it means

`experimental.cssChunking: "graph"` produces bundle-graph-aware CSS chunks, a strategy only implemented for Turbopack. If the value resolves to 'graph' but Turbopack is not active (`process.env.TURBOPACK` unset), normalization throws. Note this check is skipped during `next start` (PHASE_PRODUCTION_SERVER) and PHASE_INFO since no bundler is chosen then.

Source

Thrown at packages/next/src/server/config.ts:521

    result.sassOptions &&
    'functions' in result.sassOptions
  ) {
    throw new Error(
      `The "sassOptions.functions" option is not supported when using Turbopack. ` +
        `Custom Sass functions are only available with webpack. ` +
        `Please remove the "functions" property from your sassOptions in ${configFileName}.`
    )
  }

  // Validate experimental.cssChunking compatibility with the active bundler. Graph mode is
  // Turbopack-only; strict mode and `false` (single-chunk-per-module) are webpack-only.
  // Only validate during build/dev — `next start` doesn't pick a bundler and would otherwise
  // see `process.env.TURBOPACK` unset and reject a valid `cssChunking: "graph"` config.
  if (phase !== PHASE_PRODUCTION_SERVER && phase !== PHASE_INFO) {
    const cssChunkingValue = result.experimental.cssChunking
    const cssChunkingMode = resolveCssChunkingMode(cssChunkingValue)
    if (cssChunkingMode === 'graph' && !process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: "graph"\` is only supported with Turbopack. ` +
          `Please remove the option or run Next.js with Turbopack in ${configFileName}.`
      )
    }
    if (cssChunkingMode === 'strict' && process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: "strict"\` is only supported with webpack. ` +
          `Please remove the option or run Next.js with webpack in ${configFileName}.`
      )
    }
    // Only error when `false` was set explicitly. `undefined` (the default) also resolves to
    // `'off'` but that's the implicit default and must not error on Turbopack.
    if (cssChunkingValue === false && process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: false\` is only supported with webpack. ` +
          `Please remove the option or run Next.js with webpack in ${configFileName}.`
      )
    }

View on GitHub (pinned to 0ae8c72462)

Solutions

Run with Turbopack (remove `--webpack`) to use graph mode
Switch to a webpack-compatible cssChunking value: omit it (default) or use a webpack-supported mode

Example fix

// before
// next build --webpack
module.exports = { experimental: { cssChunking: 'graph' } }
// after (option A)
module.exports = { experimental: { cssChunking: 'graph' } }
// run: next build  (Turbopack)
// after (option B)
module.exports = { experimental: { cssChunking: 'strict' } }
// run: next build --webpack

Defensive patterns

Strategy: validation

Validate before calling

const isTurbopack = Boolean(process.env.TURBOPACK)
if (cssChunking === 'graph' && !isTurbopack) {
  cssChunking = undefined // or switch bundler
}

Prevention

Gate cssChunking on the active bundler before setting it
Document which cssChunking modes each bundler supports in the config

When it happens

Trigger: Setting `experimental: { cssChunking: 'graph' }` and running `next build`/`next dev` with webpack (`--webpack` or default where Turbopack isn't engaged).

Common situations: Adopting CSS chunking graph mode after reading docs written for Turbopack, then running a webpack build. Forcing webpack in CI while keeping Turbopack-only options.

Related errors

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/fe71aab4650c719c. Report an issue: GitHub.