diff --git a/.github/workflows/build_and_test.yml b/.github/workflows/build_and_test.yml
index 9a0e0cbb8e95b..1f4fb64e6b07d 100644
--- a/.github/workflows/build_and_test.yml
+++ b/.github/workflows/build_and_test.yml
@@ -502,7 +502,6 @@ jobs:
 
         export NEXT_TEST_MODE=start
         export NEXT_TEST_WASM=true
-        export IS_WEBPACK_TEST=1
         node run-tests.js \
           test/production/pages-dir/production/test/index.test.ts \
           test/e2e/streaming-ssr/index.test.ts
@@ -712,7 +711,7 @@ jobs:
 
     secrets: inherit
 
-  test-dev: # TODO: rename to include webpack
+  test-dev:
     name: test dev
     needs: ['optimize-ci', 'changes', 'build-native', 'build-next']
     if: ${{ needs.optimize-ci.outputs.skip == 'false' && needs.changes.outputs.docs-only == 'false' }}
@@ -729,7 +728,6 @@ jobs:
     uses: ./.github/workflows/build_reusable.yml
     with:
       afterBuild: |
-        export IS_WEBPACK_TEST=1
         export NEXT_TEST_MODE=dev
         export NEXT_TEST_REACT_VERSION="${{ matrix.react }}"
 
@@ -754,10 +752,8 @@ jobs:
 
     uses: ./.github/workflows/build_reusable.yml
     with:
-      # Should this be using turbopack? a variation?
       afterBuild: |
         export NEXT_TEST_MODE=dev
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           test/e2e/app-dir/app/index.test.ts \
@@ -784,7 +780,6 @@ jobs:
     with:
       nodeVersion: 20.9.0
       afterBuild: |
-        export IS_WEBPACK_TEST=1
         node run-tests.js \
           --concurrency 4 \
           test/production/pages-dir/production/test/index.test.ts \
@@ -813,7 +808,6 @@ jobs:
     with:
       afterBuild: |
         export NEXT_TEST_MODE=start
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js --type production \
           test/e2e/app-dir/app/index.test.ts \
@@ -842,7 +836,6 @@ jobs:
     uses: ./.github/workflows/build_reusable.yml
     with:
       afterBuild: |
-        export IS_WEBPACK_TEST=1
         export NEXT_TEST_MODE=start
         export NEXT_TEST_REACT_VERSION="${{ matrix.react }}"
 
@@ -882,7 +875,6 @@ jobs:
     with:
       nodeVersion: 20.9.0
       afterBuild: |
-        export IS_WEBPACK_TEST=1
         export NEXT_TEST_REACT_VERSION="${{ matrix.react }}"
 
         node run-tests.js \
@@ -904,7 +896,6 @@ jobs:
 
         # these all run without concurrency because they're heavier
         export TEST_CONCURRENCY=1
-        export IS_WEBPACK_TEST=1
 
         BROWSER_NAME=firefox node run-tests.js \
           test/production/pages-dir/production/test/index.test.ts
@@ -932,7 +923,6 @@ jobs:
       afterBuild: |
         export __NEXT_EXPERIMENTAL_PPR=true
         export NEXT_EXTERNAL_TESTS_FILTERS="test/ppr-tests-manifest.json"
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
@@ -955,7 +945,6 @@ jobs:
         export __NEXT_EXPERIMENTAL_PPR=true
         export NEXT_EXTERNAL_TESTS_FILTERS="test/ppr-tests-manifest.json"
         export NEXT_TEST_MODE=dev
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
@@ -979,7 +968,6 @@ jobs:
         export __NEXT_EXPERIMENTAL_PPR=true
         export NEXT_EXTERNAL_TESTS_FILTERS="test/ppr-tests-manifest.json"
         export NEXT_TEST_MODE=start
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
@@ -1002,7 +990,6 @@ jobs:
         export __NEXT_EXPERIMENTAL_PPR=true # for compatibility with the existing tests
         export __NEXT_EXPERIMENTAL_CACHE_COMPONENTS=true
         export NEXT_EXTERNAL_TESTS_FILTERS="test/experimental-tests-manifest.json"
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
@@ -1027,7 +1014,6 @@ jobs:
         export NEXT_EXTERNAL_TESTS_FILTERS="test/experimental-tests-manifest.json"
         export NEXT_TEST_MODE=dev
         export __NEXT_EXPERIMENTAL_ISOLATED_DEV_BUILD=true
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
@@ -1052,7 +1038,6 @@ jobs:
         export __NEXT_EXPERIMENTAL_CACHE_COMPONENTS=true
         export NEXT_EXTERNAL_TESTS_FILTERS="test/experimental-tests-manifest.json"
         export NEXT_TEST_MODE=start
-        export IS_WEBPACK_TEST=1
 
         node run-tests.js \
           --timings \
diff --git a/.github/workflows/pull_request_stats.yml b/.github/workflows/pull_request_stats.yml
index 9fe1fc91701bc..3b3afeee5da3b 100644
--- a/.github/workflows/pull_request_stats.yml
+++ b/.github/workflows/pull_request_stats.yml
@@ -60,7 +60,3 @@ jobs:
 
       - uses: ./.github/actions/next-stats-action
         if: ${{ steps.docs-change.outputs.DOCS_CHANGE == 'nope' }}
-        env:
-          # This uses the webpack bundle analyzer and for consistent results we need to use webpack.
-          # Once there is an equivalent analyzer for turbopack, we can remove this.
-          IS_WEBPACK_TEST: 1
diff --git a/.github/workflows/test_e2e_deploy_release.yml b/.github/workflows/test_e2e_deploy_release.yml
index 9c0d33eeefde9..631b0a2b43f46 100644
--- a/.github/workflows/test_e2e_deploy_release.yml
+++ b/.github/workflows/test_e2e_deploy_release.yml
@@ -78,15 +78,7 @@ jobs:
       matrix:
         group: [1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8, 8/8]
     with:
-      afterBuild: |
-        npm i -g vercel@latest && \
-        NEXT_E2E_TEST_TIMEOUT=240000 \
-        NEXT_TEST_MODE=deploy \
-        IS_WEBPACK_TEST=1 \
-        NEXT_EXTERNAL_TESTS_FILTERS="test/deploy-tests-manifest.json" \
-        NEXT_TEST_VERSION="${{ github.event.inputs.nextVersion || 'canary' }}" \
-        VERCEL_CLI_VERSION="${{ github.event.inputs.vercelCliVersion || 'vercel@latest' }}" \
-        node run-tests.js --timings -g ${{ matrix.group }} -c 2 --type e2e
+      afterBuild: npm i -g vercel@latest && NEXT_E2E_TEST_TIMEOUT=240000 NEXT_TEST_MODE=deploy NEXT_EXTERNAL_TESTS_FILTERS="test/deploy-tests-manifest.json" NEXT_TEST_VERSION="${{ github.event.inputs.nextVersion || 'canary' }}" VERCEL_CLI_VERSION="${{ github.event.inputs.vercelCliVersion || 'vercel@latest' }}" node run-tests.js --timings -g ${{ matrix.group }} -c 2 --type e2e
       skipNativeBuild: 'yes'
       skipNativeInstall: 'no'
       stepName: 'test-deploy-${{ matrix.group }}'
diff --git a/bench/heavy-npm-deps/package.json b/bench/heavy-npm-deps/package.json
index 8bd442a10f8a5..2428e307218e8 100644
--- a/bench/heavy-npm-deps/package.json
+++ b/bench/heavy-npm-deps/package.json
@@ -4,9 +4,9 @@
   "private": true,
   "scripts": {
     "dev-turbopack": "next dev --turbopack",
-    "dev-webpack": "next dev --webpack",
+    "dev-webpack": "next dev",
     "build-turbopack": "next build --turbopack",
-    "build-webpack": "next build --webpack",
+    "build-webpack": "next build",
     "start-turbopack": "next start",
     "start-webpack": "next start",
     "build-application": "next build",
diff --git a/bench/module-cost/package.json b/bench/module-cost/package.json
index 96814e0e6e875..eb6e8a7478d92 100644
--- a/bench/module-cost/package.json
+++ b/bench/module-cost/package.json
@@ -3,10 +3,10 @@
   "scripts": {
     "prepare-bench": "node scripts/prepare-bench.mjs",
     "benchmark": "node scripts/benchmark-runner.mjs",
-    "dev-webpack": "next dev --webpack",
-    "dev-turbopack": "next dev --turbopack",
-    "build-webpack": "next build --webpack",
-    "build-turbopack": "next build --turbopack",
+    "dev-webpack": "next dev",
+    "dev-turbopack": "next dev --turbo",
+    "build-webpack": "next build",
+    "build-turbopack": "next build --turbo",
     "start": "next start"
   },
   "devDependencies": {
diff --git a/package.json b/package.json
index bcefe2d27693f..3a25302936fe9 100644
--- a/package.json
+++ b/package.json
@@ -17,49 +17,29 @@
     "ci:publish": "tsx ./scripts/release/publish-npm.ts",
     "test-types": "tsc",
     "test-unit": "jest test/unit/ packages/next/ packages/font",
-    "test-dev-inner": "cross-env NEXT_TEST_MODE=dev pnpm testheadless",
-    "test-dev": "pnpm run test-dev-webpack",
-    "test-dev-webpack": "pnpm run with-webpack pnpm test-dev-inner",
-    "test-dev-experimental-inner": "pnpm run with-experimental pnpm test-dev-inner",
-    "test-dev-experimental": "pnpm run test-dev-experimental-webpack",
-    "test-dev-experimental-webpack": "pnpm run with-webpack pnpm test-dev-experimental-inner",
-    "test-dev-rspack": "pnpm run with-rspack pnpm run test-dev-inner",
-    "test-dev-experimental-rspack": "pnpm run with-rspack pnpm run test-dev-experimental-inner",
-    "test-dev-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm test-dev-inner",
-    "test-dev-experimental-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm run with-experimental pnpm test-dev-inner",
-    "test-start-inner": "cross-env NEXT_TEST_MODE=start pnpm testheadless",
-    "test-start": "pnpm run test-start-webpack",
-    "test-start-webpack": "pnpm run with-webpack pnpm run test-start-inner",
-    "test-start-experimental-inner": "pnpm run with-experimental pnpm test-start-inner",
-    "test-start-experimental": "pnpm run test-start-experimental-webpack",
-    "test-start-experimental-webpack": "pnpm run with-webpack pnpm run test-start-experimental-inner",
-    "test-start-rspack": "pnpm run with-rspack pnpm run test-start-inner",
-    "test-start-experimental-rspack": "pnpm run with-rspack pnpm run test-start-experimental-inner",
-    "test-start-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm test-start-inner",
-    "test-start-experimental-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm run with-experimental pnpm test-start-experimental-inner",
-    "test-deploy-inner": "cross-env NEXT_TEST_MODE=deploy pnpm testheadless",
-    "test-deploy": "pnpm run test-deploy-webpack",
-    "test-deploy-webpack": "pnpm run with-webpack pnpm test-deploy-inner",
-    "test-deploy-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm test-deploy-inner",
-    "testonly-dev-inner": "cross-env NEXT_TEST_MODE=dev pnpm testonly",
-    "testonly-dev": "pnpm run testonly-dev-webpack",
-    "testonly-dev-webpack": "pnpm run with-webpack pnpm run testonly-dev-inner",
-    "testonly-dev-rspack": "pnpm run with-rspack pnpm run testonly-dev-inner",
-    "testonly-dev-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm testonly-dev-inner",
-    "testonly-start-inner": "cross-env NEXT_TEST_MODE=start pnpm testonly",
-    "testonly-start": "pnpm run testonly-start-webpack",
-    "testonly-start-webpack": "pnpm run with-webpack pnpm run testonly-start-inner",
-    "testonly-start-rspack": "pnpm run with-rspack pnpm run testonly-start-inner",
-    "testonly-start-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm testonly-start-inner",
-    "testonly-deploy-inner": "cross-env NEXT_TEST_MODE=deploy pnpm testonly",
-    "testonly-deploy": "pnpm run testonly-deploy-webpack",
-    "testonly-deploy-webpack": "pnpm run with-webpack pnpm run testonly-deploy-inner",
-    "testonly-deploy-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm testonly-deploy-inner",
-    "test-inner": "pnpm testheadless",
-    "test": "pnpm test-webpack",
-    "test-webpack": "pnpm run with-webpack pnpm run test-inner",
-    "test-rspack": "pnpm run with-rspack pnpm run test-inner",
-    "test-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 TURBOPACK_BUILD=1 pnpm test-inner",
+    "test-dev": "cross-env NEXT_TEST_MODE=dev pnpm testheadless",
+    "test-dev-experimental": "cross-env NEXT_TEST_MODE=dev pnpm run with-experimental pnpm testheadless",
+    "test-dev-rspack": "pnpm run with-rspack pnpm run test-dev",
+    "test-dev-experimental-rspack": "pnpm run with-rspack pnpm run test-dev-experimental",
+    "test-dev-turbo": "cross-env NEXT_TEST_MODE=dev IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm testheadless",
+    "test-dev-experimental-turbo": "cross-env NEXT_TEST_MODE=dev IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm run with-experimental pnpm testheadless",
+    "test-start": "cross-env NEXT_TEST_MODE=start pnpm testheadless",
+    "test-start-experimental": "cross-env NEXT_TEST_MODE=start pnpm run with-experimental pnpm testheadless",
+    "test-start-rspack": "pnpm run with-rspack pnpm run test-start",
+    "test-start-experimental-rspack": "pnpm run with-rspack pnpm run test-start-experimental",
+    "test-start-turbo": "cross-env NEXT_TEST_MODE=start IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm testheadless",
+    "test-start-experimental-turbo": "cross-env NEXT_TEST_MODE=start IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm run with-experimental pnpm testheadless",
+    "test-deploy": "cross-env NEXT_TEST_MODE=deploy pnpm testheadless",
+    "testonly-dev": "cross-env NEXT_TEST_MODE=dev pnpm testonly",
+    "testonly-dev-rspack": "pnpm run with-rspack pnpm run testonly-dev",
+    "testonly-dev-turbo": "cross-env NEXT_TEST_MODE=dev IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 pnpm testonly",
+    "testonly-start": "cross-env NEXT_TEST_MODE=start pnpm testonly",
+    "testonly-start-rspack": "pnpm run with-rspack pnpm run testonly-start",
+    "testonly-start-turbo": "cross-env NEXT_TEST_MODE=start IS_TURBOPACK_TEST=1 TURBOPACK_BUILD=1 pnpm testonly",
+    "testonly-deploy": "cross-env NEXT_TEST_MODE=deploy pnpm testonly",
+    "test": "pnpm testheadless",
+    "test-rspack": "pnpm run with-rspack pnpm run test",
+    "test-turbo": "cross-env IS_TURBOPACK_TEST=1 TURBOPACK_DEV=1 TURBOPACK_BUILD=1 pnpm testheadless",
     "testonly": "jest --runInBand",
     "testheadless": "cross-env HEADLESS=true pnpm testonly",
     "genstats": "cross-env LOCAL_STATS=true node .github/actions/next-stats-action/src/index.js",
@@ -109,7 +89,6 @@
     "build-storybook": "turbo run build-storybook",
     "test-storybook": "turbo run test-storybook",
     "with-rspack": "cross-env NEXT_RSPACK=1 NEXT_TEST_USE_RSPACK=1",
-    "with-webpack": "cross-env IS_WEBPACK_TEST=1",
     "with-experimental": "cross-env __NEXT_EXPERIMENTAL_CACHE_COMPONENTS=true __NEXT_EXPERIMENTAL_PPR=true"
   },
   "devDependencies": {
diff --git a/packages/next-rspack/index.js b/packages/next-rspack/index.js
index adcc47df109ec..e0ce02d637d84 100644
--- a/packages/next-rspack/index.js
+++ b/packages/next-rspack/index.js
@@ -1,13 +1,5 @@
 module.exports = function withRspack(config) {
   process.env.NEXT_RSPACK = 'true'
   process.env.RSPACK_CONFIG_VALIDATE = 'loose-silent'
-  if (process.env.TURBOPACK === 'auto') {
-    // If next has defaulted to turbopack, override it.
-    delete process.env.TURBOPACK
-  } else if (process.env.TURBOPACK) {
-    console.error('Cannot call withRspack and pass the --turbopack flag.')
-    console.error('Please configure only one bundler.')
-    process.exit(1)
-  }
   return config
 }
diff --git a/packages/next/src/bin/next.ts b/packages/next/src/bin/next.ts
index a947d1ad95aee..cfcb4b5b355b7 100755
--- a/packages/next/src/bin/next.ts
+++ b/packages/next/src/bin/next.ts
@@ -133,9 +133,8 @@ program
   .option('--no-mangling', 'Disables mangling.')
   .option('--profile', 'Enables production profiling for React.')
   .option('--experimental-app-only', 'Builds only App Router routes.')
-  .option('--turbo', 'Builds using Turbopack.')
-  .option('--turbopack', 'Builds using Turbopack.')
-  .option('--webpack', 'Builds using webpack.')
+  .option('--turbo', 'Starts development mode using Turbopack.')
+  .option('--turbopack', 'Starts development mode using Turbopack.')
   .addOption(
     new Option(
       '--experimental-build-mode [mode]',
@@ -174,7 +173,6 @@ program
   )
   .option('--turbo', 'Starts development mode using Turbopack.')
   .option('--turbopack', 'Starts development mode using Turbopack.')
-  .option('--webpack', 'Starts development mode using webpack.')
   .addOption(
     new Option(
       '-p, --port <port>',
diff --git a/packages/next/src/build/index.ts b/packages/next/src/build/index.ts
index 5394a9b2bd593..9225b231b9d6f 100644
--- a/packages/next/src/build/index.ts
+++ b/packages/next/src/build/index.ts
@@ -83,7 +83,6 @@ import {
   UNDERSCORE_GLOBAL_ERROR_ROUTE_ENTRY,
 } from '../shared/lib/entry-constants'
 import { isDynamicRoute } from '../shared/lib/router/utils'
-import { Bundler, finalizeBundlerFromConfig } from '../lib/bundler'
 import type { __ApiPreviewProps } from '../server/api-utils'
 import loadConfig from '../server/config'
 import type { BuildManifest } from '../server/get-page-files'
@@ -902,7 +901,7 @@ export default async function build(
   runLint = true,
   noMangling = false,
   appDirOnly = false,
-  bundler = Bundler.Turbopack,
+  isTurbopack = false,
   experimentalBuildMode: 'default' | 'compile' | 'generate' | 'generate-env',
   traceUploadUrl: string | undefined
 ): Promise<void> {
@@ -915,6 +914,7 @@ export default async function build(
   try {
     const nextBuildSpan = trace('next-build', undefined, {
       buildMode: experimentalBuildMode,
+      isTurboBuild: String(isTurbopack),
       version: process.env.__NEXT_VERSION as string,
     })
 
@@ -949,10 +949,6 @@ export default async function build(
         )
       loadedConfig = config
 
-      // Reading the config can modify environment variables that influence the bundler selection.
-      bundler = finalizeBundlerFromConfig(bundler)
-      nextBuildSpan.setAttribute('bundler', getBundlerForTelemetry(bundler))
-
       process.env.NEXT_DEPLOYMENT_ID = config.deploymentId || ''
       NextBuildContext.config = config
 
@@ -975,7 +971,7 @@ export default async function build(
       NextBuildContext.buildId = buildId
 
       if (experimentalBuildMode === 'generate-env') {
-        if (bundler === Bundler.Turbopack) {
+        if (isTurbopack) {
           Log.warn('generate-env is not needed with turbopack')
           process.exit(0)
         }
@@ -1402,7 +1398,7 @@ export default async function build(
         })
 
       // Turbopack already handles conflicting app and page routes.
-      if (bundler !== Bundler.Turbopack) {
+      if (!isTurbopack) {
         const numConflictingAppPaths = conflictingAppPagePaths.length
         if (mappedAppPages && numConflictingAppPaths > 0) {
           Log.error(
@@ -1685,7 +1681,7 @@ export default async function build(
 
       let shutdownPromise = Promise.resolve()
       if (!isGenerateMode) {
-        if (bundler === Bundler.Turbopack) {
+        if (isTurbopack) {
           const {
             duration: compilerDuration,
             shutdownPromise: p,
@@ -1799,7 +1795,7 @@ export default async function build(
 
             telemetry.record(
               eventBuildCompleted(pagesPaths, {
-                bundler: getBundlerForTelemetry(bundler),
+                bundler: getBundlerForTelemetry(isTurbopack),
                 durationInSeconds,
                 totalAppPagesCount,
               })
@@ -1815,7 +1811,7 @@ export default async function build(
 
             telemetry.record(
               eventBuildCompleted(pagesPaths, {
-                bundler: getBundlerForTelemetry(bundler),
+                bundler: getBundlerForTelemetry(isTurbopack),
                 durationInSeconds: compilerDuration,
                 totalAppPagesCount,
               })
@@ -2433,10 +2429,7 @@ export default async function build(
         )
         // If there's edge routes, append the edge instrumentation hook
         // Turbopack generates this chunk with a hashed name and references it in middleware-manifest.
-        if (
-          bundler !== Bundler.Turbopack &&
-          (edgeRuntimeAppCount || edgeRuntimePagesCount)
-        ) {
+        if (!isTurbopack && (edgeRuntimeAppCount || edgeRuntimePagesCount)) {
           instrumentationHookEntryFiles.push(
             path.join(
               SERVER_DIRECTORY,
@@ -2489,7 +2482,7 @@ export default async function build(
               path.join(SERVER_DIRECTORY, FUNCTIONS_CONFIG_MANIFEST),
               path.join(SERVER_DIRECTORY, MIDDLEWARE_MANIFEST),
               path.join(SERVER_DIRECTORY, MIDDLEWARE_BUILD_MANIFEST + '.js'),
-              ...(bundler !== Bundler.Turbopack
+              ...(!isTurbopack
                 ? [
                     path.join(
                       SERVER_DIRECTORY,
@@ -2524,7 +2517,7 @@ export default async function build(
                     ),
                   ]
                 : []),
-              ...(pagesDir && bundler !== Bundler.Turbopack
+              ...(pagesDir && !isTurbopack
                 ? [
                     DYNAMIC_CSS_MANIFEST + '.json',
                     path.join(SERVER_DIRECTORY, DYNAMIC_CSS_MANIFEST + '.js'),
@@ -2576,7 +2569,7 @@ export default async function build(
             ],
           }
 
-          if (bundler === Bundler.Turbopack) {
+          if (isTurbopack) {
             await writeManifest(
               path.join(
                 distDir,
@@ -2592,11 +2585,7 @@ export default async function build(
 
       await writeFunctionsConfigManifest(distDir, functionsConfigManifest)
 
-      if (
-        bundler !== Bundler.Turbopack &&
-        !isGenerateMode &&
-        !buildTracesPromise
-      ) {
+      if (!isTurbopack && !isGenerateMode && !buildTracesPromise) {
         buildTracesPromise = nextBuildSpan
           .traceChild('collect-build-traces')
           .traceAsyncFn(() => {
@@ -2737,7 +2726,7 @@ export default async function build(
 
       // we don't need to inline for turbopack build as
       // it will handle it's own caching separate of compile
-      if (isGenerateMode && bundler !== Bundler.Turbopack) {
+      if (isGenerateMode && !isTurbopack) {
         Log.info('Inlining static env ...')
 
         await nextBuildSpan
@@ -4143,7 +4132,7 @@ export default async function build(
     if (telemetry) {
       telemetry.record(
         eventBuildFailed({
-          bundler: getBundlerForTelemetry(bundler),
+          bundler: getBundlerForTelemetry(isTurbopack),
           errorCode: getErrorCodeForTelemetry(e),
           durationInSeconds: Math.floor((Date.now() - buildStartTime) / 1000),
         })
@@ -4164,7 +4153,7 @@ export default async function build(
         mode: 'build',
         projectDir: dir,
         distDir: loadedConfig.distDir,
-        isTurboSession: bundler === Bundler.Turbopack,
+        isTurboSession: isTurbopack,
         sync: true,
       })
     }
@@ -4178,17 +4167,16 @@ function errorFromUnsupportedSegmentConfig(): never {
   process.exit(1)
 }
 
-function getBundlerForTelemetry(bundler: Bundler) {
-  switch (bundler) {
-    case Bundler.Turbopack:
-      return 'turbopack'
-    case Bundler.Rspack:
-      return 'rspack'
-    case Bundler.Webpack:
-      return 'webpack'
-    default:
-      throw new Error(`unknown bundler: ${bundler}`)
+function getBundlerForTelemetry(isTurbopack: boolean) {
+  if (isTurbopack) {
+    return 'turbopack'
   }
+
+  if (process.env.NEXT_RSPACK) {
+    return 'rspack'
+  }
+
+  return 'webpack'
 }
 
 function getErrorCodeForTelemetry(err: unknown) {
diff --git a/packages/next/src/cli/next-build.ts b/packages/next/src/cli/next-build.ts
index bea9c4900e8e6..a2df58fdc4135 100755
--- a/packages/next/src/cli/next-build.ts
+++ b/packages/next/src/cli/next-build.ts
@@ -10,7 +10,6 @@ import isError from '../lib/is-error'
 import { getProjectDir } from '../lib/get-project-dir'
 import { enableMemoryDebuggingMode } from '../lib/memory/startup'
 import { disableMemoryDebuggingMode } from '../lib/memory/shutdown'
-import { parseBundlerArgs } from '../lib/bundler'
 
 export type NextBuildOptions = {
   debug?: boolean
@@ -20,7 +19,6 @@ export type NextBuildOptions = {
   mangling: boolean
   turbo?: boolean
   turbopack?: boolean
-  webpack?: boolean
   experimentalDebugMemoryUsage: boolean
   experimentalAppOnly?: boolean
   experimentalTurbo?: boolean
@@ -84,7 +82,12 @@ const nextBuild = (options: NextBuildOptions, directory?: string) => {
     printAndExit(`> No such directory exists as the project root: ${dir}`)
   }
 
-  const bundler = parseBundlerArgs(options)
+  const isTurbopack = Boolean(
+    options.turbo || options.turbopack || process.env.IS_TURBOPACK_TEST
+  )
+  if (isTurbopack) {
+    process.env.TURBOPACK = '1'
+  }
 
   return build(
     dir,
@@ -94,7 +97,7 @@ const nextBuild = (options: NextBuildOptions, directory?: string) => {
     lint,
     !mangling,
     experimentalAppOnly,
-    bundler,
+    isTurbopack,
     experimentalBuildMode,
     traceUploadUrl
   )
diff --git a/packages/next/src/cli/next-dev.ts b/packages/next/src/cli/next-dev.ts
index b4f1e0db71f6d..33e6e51bc6d88 100644
--- a/packages/next/src/cli/next-dev.ts
+++ b/packages/next/src/cli/next-dev.ts
@@ -38,17 +38,11 @@ import { once } from 'node:events'
 import { clearTimeout } from 'timers'
 import { flushAllTraces, trace } from '../trace'
 import { traceId } from '../trace/shared'
-import {
-  Bundler,
-  finalizeBundlerFromConfig,
-  parseBundlerArgs,
-} from '../lib/bundler'
 
 export type NextDevOptions = {
   disableSourceMaps: boolean
   turbo?: boolean
   turbopack?: boolean
-  webpack?: boolean
   port: number
   hostname?: string
   experimentalHttps?: boolean
@@ -64,11 +58,11 @@ let dir: string
 let child: undefined | ChildProcess
 // The config in next-dev is only used to access config.distDir for telemetry and trace.
 let config: NextConfigComplete
-let bundler: Bundler
+let isTurboSession = false
 let traceUploadUrl: string
 let sessionStopHandled = false
-const sessionStarted = Date.now()
-const sessionSpan = trace('next-dev')
+let sessionStarted = Date.now()
+let sessionSpan = trace('next-dev')
 
 // How long should we wait for the child to cleanly exit after sending
 // SIGINT/SIGTERM to the child process before sending SIGKILL?
@@ -129,13 +123,11 @@ const handleSessionStop = async (signal: NodeJS.Signals | number | null) => {
       new Telemetry({
         distDir: path.join(dir, config.distDir),
       })
-    // Reading the config can modify environment variables that influence the bundler selection.
-    bundler = finalizeBundlerFromConfig(bundler)
 
     telemetry.record(
       eventCliSessionStopped({
         cliCommand: 'dev',
-        turboFlag: bundler === Bundler.Turbopack,
+        turboFlag: isTurboSession,
         durationMilliseconds: Date.now() - sessionStarted,
         pagesDir,
         appDir,
@@ -154,7 +146,7 @@ const handleSessionStop = async (signal: NodeJS.Signals | number | null) => {
       mode: 'dev',
       projectDir: dir,
       distDir: config.distDir,
-      isTurboSession: bundler === Bundler.Turbopack,
+      isTurboSession,
     })
   }
 
@@ -176,7 +168,14 @@ const nextDev = async (
   portSource: PortSource,
   directory?: string
 ) => {
-  bundler = parseBundlerArgs(options)
+  const isTurbopack = Boolean(
+    options.turbo || options.turbopack || process.env.IS_TURBOPACK_TEST
+  )
+  if (isTurbopack) {
+    process.env.TURBOPACK = '1'
+  }
+
+  isTurboSession = isTurbopack
 
   dir = getProjectDir(process.env.NEXT_PRIVATE_DEV_DIR || directory)
 
@@ -289,9 +288,7 @@ const nextDev = async (
         stdio: 'inherit',
         env: {
           ...defaultEnv,
-          ...(bundler === Bundler.Turbopack
-            ? { TURBOPACK: process.env.TURBOPACK }
-            : undefined),
+          ...(isTurbopack ? { TURBOPACK: '1' } : undefined),
           NEXT_PRIVATE_WORKER: '1',
           NEXT_PRIVATE_TRACE_ID: traceId,
           NODE_EXTRA_CA_CERTS: startServerOptions.selfSignedCertificate
@@ -339,13 +336,12 @@ const nextDev = async (
               (await loadConfig(PHASE_DEVELOPMENT_SERVER, dir, {
                 silent: true,
               }))
-            bundler = finalizeBundlerFromConfig(bundler)
             uploadTrace({
               traceUploadUrl,
               mode: 'dev',
               projectDir: dir,
               distDir: config.distDir,
-              isTurboSession: bundler === Bundler.Turbopack,
+              isTurboSession,
               sync: true,
             })
           }
diff --git a/packages/next/src/lib/bundler.ts b/packages/next/src/lib/bundler.ts
deleted file mode 100644
index 38eee0866d2e6..0000000000000
--- a/packages/next/src/lib/bundler.ts
+++ /dev/null
@@ -1,99 +0,0 @@
-/// Utilties for configuring the bundler to use.
-export enum Bundler {
-  Turbopack,
-  Webpack,
-  Rspack,
-}
-/**
- * Parse the bundler arguments and potentially sets the `TURBOPACK` environment variable.
- *
- * NOTE: rspack is configured via next config which is chaotic so it is possible for this to be overridden later.
- *
- * @param options The options to parse.
- * @returns The bundler that was configured
- */
-export function parseBundlerArgs(options: {
-  turbo?: boolean
-  turbopack?: boolean
-  webpack?: boolean
-}): Bundler {
-  const bundlerFlags = new Map<Bundler, string[]>()
-  const setBundlerFlag = (bundler: Bundler, flag: string) => {
-    bundlerFlags.set(bundler, (bundlerFlags.get(bundler) ?? []).concat(flag))
-  }
-  // What turbo flag was set? We allow multiple to be set, which is silly but not ambiguous, just pick the most relevant one.
-  if (options.turbopack) {
-    setBundlerFlag(Bundler.Turbopack, '--turbopack')
-  }
-  if (options.turbo) {
-    setBundlerFlag(Bundler.Turbopack, '--turbo')
-  } else if (process.env.TURBOPACK) {
-    // We don't really want to support this but it is trivial and not really confusing.
-    // If we don't support it and someone sets it, we would have inconsistent behavior
-    // since some parts of next would read the return value of this function and other
-    // parts will read the env variable.
-    setBundlerFlag(Bundler.Turbopack, `TURBOPACK=${process.env.TURBOPACK}`)
-  } else if (process.env.IS_TURBOPACK_TEST) {
-    setBundlerFlag(
-      Bundler.Turbopack,
-      `IS_TURBOPACK_TEST=${process.env.IS_TURBOPACK_TEST}`
-    )
-  }
-  if (options.webpack) {
-    setBundlerFlag(Bundler.Webpack, '--webpack')
-  }
-
-  if (process.env.IS_WEBPACK_TEST) {
-    setBundlerFlag(
-      Bundler.Webpack,
-      `IS_WEBPACK_TEST=${process.env.IS_WEBPACK_TEST}`
-    )
-  }
-
-  // Mostly this is set via the NextConfig but it can also be set via the command line which is
-  // common for testing.
-  if (process.env.NEXT_RSPACK) {
-    setBundlerFlag(Bundler.Rspack, `NEXT_RSPACK=${process.env.NEXT_RSPACK}`)
-  }
-  if (process.env.NEXT_TEST_USE_RSPACK) {
-    setBundlerFlag(
-      Bundler.Rspack,
-      `NEXT_TEST_USE_RSPACK=${process.env.NEXT_TEST_USE_RSPACK}`
-    )
-  }
-
-  if (bundlerFlags.size > 1) {
-    console.error(
-      `Multiple bundler flags set: ${Array.from(bundlerFlags.values()).flat().join(', ')}. Configure exactly one bundler.`
-    )
-    process.exit(1)
-  }
-  // The default is turbopack when nothing is configured.
-  if (bundlerFlags.size === 0) {
-    process.env.TURBOPACK = 'auto'
-    return Bundler.Turbopack
-  }
-  if (bundlerFlags.has(Bundler.Turbopack)) {
-    // Only conditionally assign to the environment variable, preserving already set values.
-    // If it was set to 'auto' because no flag was set and this function is called a second time we
-    // would upgrade to '1' but we don't really want that.
-    process.env.TURBOPACK ??= '1'
-    return Bundler.Turbopack
-  }
-  // Otherwise it is one of rspack or webpack. At this point there must be exactly one key in the map.
-  return bundlerFlags.keys().next().value!
-}
-
-/**
- * Finalize the bundler based on the config.
- *
- * Rspack is configured via next config by setting an environment variable (yay, side effects)
- * so this should only be called after parsing the config.
- */
-export function finalizeBundlerFromConfig(fromOptions: Bundler) {
-  // Reading the next config can set NEXT_RSPACK environment variables.
-  if (process.env.NEXT_RSPACK) {
-    return Bundler.Rspack
-  }
-  return fromOptions
-}
diff --git a/packages/next/src/lib/turbopack-warning.ts b/packages/next/src/lib/turbopack-warning.ts
index 4858c0265b3dd..d737c3505a49a 100644
--- a/packages/next/src/lib/turbopack-warning.ts
+++ b/packages/next/src/lib/turbopack-warning.ts
@@ -1,4 +1,4 @@
-import type { NextConfigComplete } from '../server/config-shared'
+import type { NextConfig } from '../server/config-shared'
 import loadConfig from '../server/config'
 import * as Log from '../build/output/log'
 import {
@@ -43,9 +43,11 @@ const unsupportedTurbopackNextConfigOptions = [
 ]
 
 // The following will need to be supported by `next build --turbopack`
-const unsupportedProductionSpecificTurbopackNextConfigOptions: string[] = []
+const unsupportedProductionSpecificTurbopackNextConfigOptions: string[] = [
+  // TODO: Support disabling sourcemaps, currently they're always enabled.
+  // 'productionBrowserSourceMaps',
+]
 
-/**  */
 export async function validateTurboNextConfig({
   dir,
   isDev,
@@ -65,8 +67,8 @@ export async function validateTurboNextConfig({
   let hasWebpackConfig = false
   let hasTurboConfig = false
 
-  const unsupportedConfig: string[] = []
-  let rawNextConfig: NextConfigComplete = {} as NextConfigComplete
+  let unsupportedConfig: string[] = []
+  let rawNextConfig: NextConfig = {}
 
   const phase = isDev ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_BUILD
   try {
@@ -74,7 +76,7 @@ export async function validateTurboNextConfig({
       await loadConfig(phase, dir, {
         rawConfig: true,
       })
-    )
+    ) as NextConfig
 
     if (typeof rawNextConfig === 'function') {
       rawNextConfig = (rawNextConfig as any)(phase, {
@@ -118,7 +120,7 @@ export async function validateTurboNextConfig({
 
     const customKeys = flattenKeys(rawNextConfig)
 
-    const unsupportedKeys = isDev
+    let unsupportedKeys = isDev
       ? unsupportedTurbopackNextConfigOptions
       : [
           ...unsupportedTurbopackNextConfigOptions,
@@ -133,7 +135,7 @@ export async function validateTurboNextConfig({
         hasTurboConfig = true
       }
 
-      const isUnsupported =
+      let isUnsupported =
         unsupportedKeys.some(
           (unsupportedKey) =>
             // Either the key matches (or is a more specific subkey) of
@@ -156,24 +158,13 @@ export async function validateTurboNextConfig({
     Log.error('Unexpected error occurred while checking config', e)
   }
 
-  // If the build was defaulted to Turbopack, we want to warn about possibly ignored webpack
-  // configuration. Otherwise the user explicitly picked turbopack and thus we expect that
-  // they have configured it correctly.
-  if (process.env.TURBOPACK === 'auto' && hasWebpackConfig && !hasTurboConfig) {
-    const configFile = rawNextConfig.configFileName ?? 'your Next config file'
-    Log.error(
-      `ERROR: This build is using Turbopack, with a \`webpack\` config and no \`turbopack\` config. This may be a mistake.
-
-  As of Next.js 16 turbopack is enabled by default and custom webpack configurations may need to be migrated to Turbopack.
-
-  NOTE: your \`webpack\` config may have been added by a configuration plugin.
-
-  To configure Turbopack, see https://nextjs.org/docs/app/api-reference/next-config-js/turbopack
-
-  TIP: Many applications work fine under Turbopack with no configuration, if that is the case for you, you can silence this error by passing the \`--turbopack\` or \`--webpack\` flag explicitly or simply setting an empty turbopack config in ${configFile} (e.g. \`turbopack: {}\`).`
+  if (hasWebpackConfig && !hasTurboConfig) {
+    Log.warn(
+      `Webpack is configured while Turbopack is not, which may cause problems.`
+    )
+    Log.warn(
+      `See instructions if you need to configure Turbopack:\n  https://nextjs.org/docs/app/api-reference/next-config-js/turbopack\n`
     )
-
-    process.exit(1)
   }
 
   if (unsupportedConfig.length) {
diff --git a/packages/next/src/server/next.ts b/packages/next/src/server/next.ts
index 2ca7d7b9bffb9..88de1cd32a45d 100644
--- a/packages/next/src/server/next.ts
+++ b/packages/next/src/server/next.ts
@@ -540,8 +540,7 @@ function createServer(
     options &&
     (options.turbo || options.turbopack || process.env.IS_TURBOPACK_TEST)
   ) {
-    // Configure TURBOPACK if it isn't already set
-    process.env.TURBOPACK ??= '1'
+    process.env.TURBOPACK = '1'
   }
   // The package is used as a TypeScript plugin.
   if (
diff --git a/scripts/test-new-tests.mjs b/scripts/test-new-tests.mjs
index 881ae9dc3b21a..f62b101ea0f9e 100644
--- a/scripts/test-new-tests.mjs
+++ b/scripts/test-new-tests.mjs
@@ -153,7 +153,6 @@ async function main() {
         NEXT_EXTERNAL_TESTS_FILTERS,
         NEXT_TEST_MODE: testMode,
         NEXT_TEST_VERSION: nextTestVersion,
-        IS_WEBPACK_TEST: '1',
       },
     })
   }
@@ -171,7 +170,6 @@ async function main() {
           NEXT_TEST_VERSION: nextTestVersion,
           IS_TURBOPACK_TEST: '1',
           TURBOPACK_BUILD: testMode === 'start' ? '1' : undefined,
-          TURBOPACK_DEV: testMode === 'dev' ? '1' : undefined,
         },
       })
     }
diff --git a/test/development/next-config-ts/turbo/index.test.ts b/test/development/next-config-ts/turbo/index.test.ts
index 348568ae507ed..f43c75d6176fd 100644
--- a/test/development/next-config-ts/turbo/index.test.ts
+++ b/test/development/next-config-ts/turbo/index.test.ts
@@ -1,15 +1,13 @@
 import { nextTestSetup } from 'e2e-utils'
-;(process.env.IS_TURBOPACK_TEST ? describe : describe.skip)(
-  'next-config-ts - turbopack',
-  () => {
-    const { next } = nextTestSetup({
-      files: __dirname,
-      // explicitly ensure that turbopack is used
-      startCommand: 'pnpm next dev --turbopack',
-    })
-    it('should work with Turbopack', async () => {
-      const $ = await next.render$('/')
-      expect($('p').text()).toBe('foo')
-    })
-  }
-)
+
+describe('next-config-ts - turbopack', () => {
+  const { next } = nextTestSetup({
+    files: __dirname,
+    // explicitly ensure that turbopack is used
+    startCommand: 'pnpm next dev --turbo',
+  })
+  it('should work with Turbopack', async () => {
+    const $ = await next.render$('/')
+    expect($('p').text()).toBe('foo')
+  })
+})
diff --git a/test/e2e/config-turbopack/index.test.ts b/test/e2e/config-turbopack/index.test.ts
index 64089fd3d0129..36dacfd63a972 100644
--- a/test/e2e/config-turbopack/index.test.ts
+++ b/test/e2e/config-turbopack/index.test.ts
@@ -1,142 +1,96 @@
 /* eslint-disable jest/no-standalone-expect */
 import { nextTestSetup } from 'e2e-utils'
 
-const WARNING_MESSAGE =
-  'ERROR: This build is using Turbopack, with a `webpack` config and no `turbopack` config. This may be a mistake'
+const WARNING_MESSAGE = 'Webpack is configured while Turbopack is not'
 
 const itif = (condition: boolean) => (condition ? it : it.skip)
 
-const page = {
-  'app/page.js': `
-export default function Page() {
-  return <p>hello world</p>
-}
-`,
-}
-
-;(process.env.IS_TURBOPACK_TEST ? describe : describe.skip)(
-  'config-turbopack',
-  () => {
-    describe('when turbopack is auto selected', () => {
-      describe('when webpack is configured but Turbopack is not', () => {
-        const { next, isNextDev, isNextStart } = nextTestSetup({
-          skipStart: Boolean(process.env.NEXT_TEST_MODE === 'start'),
-          turbo: false,
-          env: {
-            TURBOPACK: 'auto',
-          },
-          files: {
-            ...page,
-            'next.config.js': `
+describe('config-turbopack', () => {
+  describe('when webpack is configured but Turbopack is not', () => {
+    const { next, isTurbopack } = nextTestSetup({
+      files: {
+        'app/page.js': `
+          export default function Page() {
+            return <p>hello world</p>
+          }
+        `,
+        'next.config.js': `
           module.exports = {
             webpack: (config) => {
               return config
             },
           }
         `,
-          },
-        })
-
-        itif(isNextDev)('warns', async () => {
-          if (next)
-            try {
-              await next.render('/')
-            } catch (e) {
-              // we expect an error but this is the only way to get the server to crash
-            }
+      },
+    })
 
-          expect(next.cliOutput).toContain(WARNING_MESSAGE)
-        })
-        itif(isNextStart)('errors', async () => {
-          const { exitCode, cliOutput } = await next.build()
-          expect(exitCode).toBe(1)
-          expect(cliOutput).toContain(WARNING_MESSAGE)
-        })
-      })
-      // no warn cases work when auto selected too
-      noWarnCases()
+    itif(isTurbopack)('warns', async () => {
+      if (next) await next.render('/')
+      expect(next.cliOutput).toContain(WARNING_MESSAGE)
     })
+  })
 
-    describe('when turbopack is explicitly configured', () => {
-      describe('when webpack is configured but Turbopack is not', () => {
-        const { next } = nextTestSetup({
-          files: {
-            ...page,
-            'next.config.js': `
-              module.exports = {
-                webpack: (config) => {
-                  return config
-                },
+  describe('when webpack is configured and config.turbopack is set', () => {
+    const { next, isTurbopack } = nextTestSetup({
+      files: {
+        'app/page.js': `
+          export default function Page() {
+            return <p>hello world</p>
+          }
+        `,
+        'next.config.js': `
+          module.exports = {
+            turbopack: {
+              rules: {
+                '*.foo': {
+                  loaders: ['foo-loader']
+                }
               }
-            `,
-          },
-        })
+            },
+            webpack: (config) => {
+              return config
+            },
+          }
+        `,
+      },
+    })
 
-        it('does not warn', async () => {
-          if (next) await next.render('/')
-          expect(next.cliOutput).not.toContain(WARNING_MESSAGE)
-        })
-      })
-      noWarnCases()
+    itif(isTurbopack)('does not warn', async () => {
+      if (next) await next.render('/')
+      expect(next.cliOutput).not.toContain(WARNING_MESSAGE)
     })
-    /// These other cases don't warn because --turbopack is explicitly selected
-    function noWarnCases(env?: Record<string, string>) {
-      describe('when webpack is configured and config.turbopack is set', () => {
-        const { next } = nextTestSetup({
-          env,
-          files: {
-            ...page,
-            'next.config.js': `
-            module.exports = {
-              turbopack: {
+  })
+
+  describe('when webpack is configured and config.experimental.turbo is set', () => {
+    const { next, isTurbopack } = nextTestSetup({
+      files: {
+        'app/page.js': `
+          export default function Page() {
+            return <p>hello world</p>
+          }
+        `,
+        'next.config.js': `
+          module.exports = {
+            experimental: {
+              turbo: {
                 rules: {
                   '*.foo': {
                     loaders: ['foo-loader']
                   }
                 }
-              },
-              webpack: (config) => {
-                return config
-              },
-            }
-          `,
-          },
-        })
-
-        it('does not warn', async () => {
-          if (next) await next.render('/')
-          expect(next.cliOutput).not.toContain(WARNING_MESSAGE)
-        })
-      })
-
-      describe('when webpack is configured and config.experimental.turbo is set', () => {
-        const { next } = nextTestSetup({
-          files: {
-            ...page,
-            'next.config.js': `
-            module.exports = {
-              experimental: {
-                turbo: {
-                  rules: {
-                    '*.foo': {
-                      loaders: ['foo-loader']
-                    }
-                  }
-                }
-              },
-              webpack: (config) => {
-                return config
-              },
-            }
-          `,
-          },
-        })
+              }
+            },
+            webpack: (config) => {
+              return config
+            },
+          }
+        `,
+      },
+    })
 
-        it('does not warn', async () => {
-          if (next) await next.render('/')
-          expect(next.cliOutput).not.toContain(WARNING_MESSAGE)
-        })
-      })
-    }
-  }
-)
+    itif(isTurbopack)('does not warn', async () => {
+      if (next) await next.render('/')
+      expect(next.cliOutput).not.toContain(WARNING_MESSAGE)
+    })
+  })
+})