diff --git a/dev-packages/e2e-tests/test-applications/sveltekit-3/src/env.ts b/dev-packages/e2e-tests/test-applications/sveltekit-3/src/env.ts
index 7ef441db0a82..ce7e354ed8b6 100644
--- a/dev-packages/e2e-tests/test-applications/sveltekit-3/src/env.ts
+++ b/dev-packages/e2e-tests/test-applications/sveltekit-3/src/env.ts
@@ -1,4 +1,4 @@
-import { defineEnvVars } from '@sveltejs/kit/hooks';
+import { defineEnvVars } from '@sveltejs/kit/env';
 
 // SvelteKit 3 makes "explicit environment variables" the default and removes the
 // legacy `$env/*` virtual modules. Declared vars are imported from `$app/env/private`
diff --git a/dev-packages/e2e-tests/test-applications/sveltekit-3/tests/errors.server.test.ts b/dev-packages/e2e-tests/test-applications/sveltekit-3/tests/errors.server.test.ts
index d660cb6198d1..447f4fa07890 100644
--- a/dev-packages/e2e-tests/test-applications/sveltekit-3/tests/errors.server.test.ts
+++ b/dev-packages/e2e-tests/test-applications/sveltekit-3/tests/errors.server.test.ts
@@ -70,7 +70,7 @@ test.describe('server-side errors', () => {
 
     expect(errorEventFrames?.[errorEventFrames?.length - 1]).toEqual(
       expect.objectContaining({
-        filename: expect.stringMatching(/app:\/\/\/_server.ts-.+.js/),
+        filename: 'app:///src/routes/server-route-error/+server.ts',
         function: 'GET',
         in_app: true,
       }),
diff --git a/packages/sveltekit/src/server-common/integrations/rewriteFramesIntegration.ts b/packages/sveltekit/src/server-common/integrations/rewriteFramesIntegration.ts
index 67a72bcd6ed2..f9f6873d2933 100644
--- a/packages/sveltekit/src/server-common/integrations/rewriteFramesIntegration.ts
+++ b/packages/sveltekit/src/server-common/integrations/rewriteFramesIntegration.ts
@@ -68,6 +68,13 @@ export function rewriteFramesIteratee(frame: StackFrame): StackFrame {
       strippedFilename = basename(filename);
     }
     frame.filename = `${prefix}${strippedFilename}`;
+  } else if (isAppRelativeSourceFrame(frame.filename)) {
+    // SvelteKit 3 (Vite/Rolldown) source-maps server frames to relative project paths such as
+    // `src/routes/+page.ts` instead of the previous bundled absolute chunk paths. These skip the
+    // branch above, so the default parser marks them as `in_app: false` (relative paths look like
+    // Node internals). Prefix them like the absolute frames and flag them as app code.
+    frame.filename = `${prefix}${frame.filename.replace(/^\.\//, '')}`;
+    frame.in_app = true;
   }
 
   delete frame.module;
@@ -80,3 +87,12 @@ export function rewriteFramesIteratee(frame: StackFrame): StackFrame {
 
   return frame;
 }
+
+/**
+ * Whether a (non-absolute) frame filename is an app-relative source path like `src/routes/+page.ts`,
+ * as opposed to a dependency or a Node built-in. Excludes `node_modules` and any scheme/drive prefix
+ * (e.g. `node:`, `data:`, `C:/`).
+ */
+function isAppRelativeSourceFrame(filename: string): boolean {
+  return !filename.includes('node_modules/') && !/^[a-zA-Z][a-zA-Z0-9.+-]*:/.test(filename);
+}
diff --git a/packages/sveltekit/test/server-common/integrations/rewriteFramesIntegration.test.ts b/packages/sveltekit/test/server-common/integrations/rewriteFramesIntegration.test.ts
index 836152a81eb0..7ea92b899524 100644
--- a/packages/sveltekit/test/server-common/integrations/rewriteFramesIntegration.test.ts
+++ b/packages/sveltekit/test/server-common/integrations/rewriteFramesIntegration.test.ts
@@ -52,6 +52,45 @@ describe('rewriteFramesIteratee', () => {
     expect(result).toStrictEqual(originalResult);
   });
 
+  it.each([
+    ['src/routes/universal-load-error/+page.ts', 'app:///src/routes/universal-load-error/+page.ts'],
+    ['./src/routes/server-load-error/+page.server.ts', 'app:///src/routes/server-load-error/+page.server.ts'],
+    ['src/hooks.server.ts', 'app:///src/hooks.server.ts'],
+  ])('rewrites and flags SvelteKit 3 app-relative source frames as in_app (%s)', (frameFilename, modifiedFilename) => {
+    const frame: StackFrame = {
+      filename: frameFilename,
+      lineno: 2,
+      colno: 9,
+      function: 'load',
+    };
+
+    const result = rewriteFramesIteratee({ ...frame });
+
+    expect(result).toStrictEqual({
+      filename: modifiedFilename,
+      lineno: 2,
+      colno: 9,
+      function: 'load',
+      in_app: true,
+    });
+  });
+
+  it.each([['node_modules/@sveltejs/kit/src/runtime/server/index.js'], ['node:internal/process/task_queues']])(
+    'does not rewrite or flag dependency/internal relative frames (%s)',
+    frameFilename => {
+      const frame: StackFrame = {
+        filename: frameFilename,
+        lineno: 1,
+        colno: 1,
+      };
+
+      const result = rewriteFramesIteratee({ ...frame });
+
+      expect(result.filename).toBe(frameFilename);
+      expect(result.in_app).toBeUndefined();
+    },
+  );
+
   it.each([
     ['adapter-node', 'build', '/absolute/path/to/build/server/chunks/3-ab34d22f.js', 'app:///chunks/3-ab34d22f.js'],
     [