diff --git a/dev-packages/e2e-tests/test-applications/nextjs-16/tests/turbopack-dev-in-app.test.ts b/dev-packages/e2e-tests/test-applications/nextjs-16/tests/turbopack-dev-in-app.test.ts
new file mode 100644
index 000000000000..c7967705963f
--- /dev/null
+++ b/dev-packages/e2e-tests/test-applications/nextjs-16/tests/turbopack-dev-in-app.test.ts
@@ -0,0 +1,43 @@
+import test, { expect } from '@playwright/test';
+import { waitForError } from '@sentry-internal/test-utils';
+import { isTurbopackDevMode } from './isDevMode';
+
+// Regression test for https://github.com/getsentry/sentry-javascript/issues/23176
+//
+// Under `next dev` with Turbopack, server stack frames get their `in_app` classification inverted:
+// Turbopack names vendor chunks `node_modules_<pkg>_<hash>.js` (underscores, no `node_modules/`
+// segment) and prefixes app modules with `[project]/`. `filenameIsInApp` keys off a literal
+// `node_modules/` substring and treats bracket-prefixed paths as internal, so vendor code is
+// marked `in_app: true` and the real app crash site is marked `in_app: false`.
+test('Turbopack dev: server stack frames are classified in_app correctly', async ({ page }) => {
+  test.skip(
+    !isTurbopackDevMode,
+    'Turbopack chunk naming (node_modules_ / [project]) only occurs in Turbopack dev mode',
+  );
+
+  const errorPromise = waitForError('nextjs-16', errorEvent => {
+    return !!errorEvent?.exception?.values?.some(value => value.value?.includes('Tool call failed'));
+  });
+
+  await page.goto('/ai-error-test');
+
+  const errorEvent = await errorPromise;
+
+  const frames = errorEvent.exception?.values?.flatMap(value => value.stacktrace?.frames ?? []) ?? [];
+  expect(frames.length).toBeGreaterThan(0);
+
+  // The crash site is app code: the `execute` tool callback defined in `app/ai-error-test/page.tsx`.
+  // It must be `in_app` so the issue leads with the real crash frame instead of vendor code.
+  const appFrame = frames.find(frame => frame.filename?.includes('ai-error-test'));
+  expect(
+    appFrame,
+    `expected an app frame for the route file, got: ${JSON.stringify(frames.map(frame => frame.filename))}`,
+  ).toBeDefined();
+  expect(appFrame?.in_app).toBe(true);
+
+  // Vendor frames from the `ai` package (Turbopack: `...node_modules_ai_...`) must not be `in_app`.
+  const vendorFrames = frames.filter(frame => frame.filename?.includes('node_modules'));
+  for (const vendorFrame of vendorFrames) {
+    expect(vendorFrame.in_app, `vendor frame ${vendorFrame.filename} should not be in_app`).toBe(false);
+  }
+});
diff --git a/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts b/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
index 7e7d221b9bba..f70990a173e8 100644
--- a/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
+++ b/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
@@ -121,15 +121,20 @@ export async function devErrorSymbolicationEventProcessor(event: Event, hint: Ev
               resolvedFrame.originalCodeFrame,
             );
 
+            const resolvedFilename = resolvedFrame.originalStackFrame.file
+              ? stripWebpackInternalPrefix(resolvedFrame.originalStackFrame.file)
+              : undefined;
+
             return {
               ...frame,
               pre_context: preContextLines,
               context_line: contextLine,
               post_context: postContextLines,
               function: resolvedFrame.originalStackFrame.methodName,
-              filename: resolvedFrame.originalStackFrame.file
-                ? stripWebpackInternalPrefix(resolvedFrame.originalStackFrame.file)
-                : undefined,
+              filename: resolvedFilename,
+              // The parse-time `in_app` is derived from Turbopack's dev chunk names (`node_modules_<pkg>_<hash>.js`,
+              // `[project]/…`), which invert the classification. Re-derive it from the resolved original source path.
+              in_app: resolvedFilename ? !resolvedFilename.includes('node_modules') : frame.in_app,
               lineno:
                 resolvedFrame.originalStackFrame.lineNumber || resolvedFrame.originalStackFrame.line1 || undefined,
               colno: resolvedFrame.originalStackFrame.column || resolvedFrame.originalStackFrame.column1 || undefined,