diff --git a/.changeset/fix-reanimated-pod-install.md b/.changeset/fix-reanimated-pod-install.md
new file mode 100644
index 0000000..ed25ad4
--- /dev/null
+++ b/.changeset/fix-reanimated-pod-install.md
@@ -0,0 +1,5 @@
+---
+"vitest-mobile": patch
+---
+
+Fix `bootstrap` failing on iOS for projects that depend on `react-native-reanimated@4`. The React Native community CLI's `--force-pods` path calls `pod install` with `RCT_NEW_ARCH_ENABLED='0'` even when the template defaults the New Architecture to on, which trips Reanimated's podspec assertion. The harness builder now prepends `ENV['RCT_NEW_ARCH_ENABLED'] = '1'` to the scaffolded Podfile so the env is corrected inside the same pod-install process, before any podspecs are evaluated.
diff --git a/packages/vitest-mobile/src/node/harness-builder/ios.ts b/packages/vitest-mobile/src/node/harness-builder/ios.ts
index 1ca72c8..96266d3 100644
--- a/packages/vitest-mobile/src/node/harness-builder/ios.ts
+++ b/packages/vitest-mobile/src/node/harness-builder/ios.ts
@@ -4,7 +4,7 @@
  */
 
 import { execSync } from 'node:child_process';
-import { existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { existsSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
 import { resolve } from 'node:path';
 import { log } from '../logger';
 import { applyTemplateTree, fillFilePlaceholders } from '../templates';
@@ -46,14 +46,13 @@ export function customizeIOS(projectDir: string, cacheKey: string): void {
   if (existsSync(podfilePath)) {
     let podfile = readFileSync(podfilePath, 'utf8');
     podfile = podfile.replace(/platform\s+:ios,\s*.+/, "platform :ios, '16.0'");
+    podfile = injectNewArchEnvOverride(podfile);
     podfile = injectFmtCxx17Fix(podfile);
     writeFileSync(podfilePath, podfile);
   }
 
   updateIOSBundleId(projectDir);
 
-  seedNewArchSnifferBait(iosDir);
-
   // PlistBuddy is macOS-only; skip on Linux (Android-only CI runners still
   // customize both platforms for the shared project, but only build one).
   if (process.platform === 'darwin') {
@@ -80,9 +79,8 @@ export async function buildIOS(projectDir: string): Promise<void> {
   // xcodebuild to fail with "Unable to load contents of file list" against
   // the Pods xcfilelists.
   //
-  // For why `customizeIOS` pre-seeds a sniffer-bait pbxproj instead of us
-  // running pod install ourselves with the right env, see
-  // `seedNewArchSnifferBait` below.
+  // For why `customizeIOS` injects an `RCT_NEW_ARCH_ENABLED` override at
+  // the top of the Podfile, see `injectNewArchEnvOverride`.
   const buildCmd = [
     'npx --yes react-native build-ios',
     `--scheme ${HARNESS_APP_NAME}`,
@@ -135,55 +133,33 @@ export function trimIOSBuildArtifacts(projectDir: string): void {
 // ── Internals ───────────────────────────────────────────────────────
 
 /**
- * Pre-seed `ios/Pods/Pods.xcodeproj/project.pbxproj` with a one-line file
- * containing the literal string `-DRCT_NEW_ARCH_ENABLED=1`. This defeats the
- * React Native community CLI's New-Architecture detection sniffer so that
- * `react-native build-ios --force-pods` runs `pod install` with new arch on
- * (matching the `RCTNewArchEnabled=true` the template writes to Info.plist).
- *
- * Why we need this: the CLI's `installPods` step hard-overrides
- * `RCT_NEW_ARCH_ENABLED` to `'0'` or `'1'` in the pod-install child env
- * based on the result of `getArchitecture(iosSourceDir)`, which is literally
- *
- *   const project = await readFile('<iosDir>/Pods/Pods.xcodeproj/project.pbxproj');
- *   return project.includes('-DRCT_NEW_ARCH_ENABLED=1');
+ * Prepend `ENV['RCT_NEW_ARCH_ENABLED'] = '1'` to the Podfile so the New
+ * Architecture is on regardless of what the React Native community CLI
+ * tells `pod install` via the child-process env.
  *
- * — see `@react-native-community/cli-platform-apple/tools/getArchitecture.ts`.
- * On a virgin scaffold that file doesn't exist (CocoaPods only creates it
- * during `pod install`), the sniffer returns `false`, the CLI passes
- * `RCT_NEW_ARCH_ENABLED='0'`, and Reanimated 4.x's podspec assertion
- * aborts the install:
- *
- *   [!] Invalid `RNReanimated.podspec` file: [Reanimated] Reanimated requires
- *   the New Architecture to be enabled. If you have `RCT_NEW_ARCH_ENABLED=0`
- *   set in your environment you should remove it.
- *
- * Pre-seeding a dummy file that contains the marker substring is enough to
- * make the sniffer return `true` on the first build. After `pod install`
- * runs successfully with new arch on, CocoaPods regenerates this file with
- * a real Xcode project that also contains `-DRCT_NEW_ARCH_ENABLED=1` (in the
- * pod target's `OTHER_CFLAGS`), so subsequent rebuilds keep returning `true`
- * — the workaround is self-sustaining.
+ * Why we need this: in the `--force-pods` / `--only-pods` path the CLI's
+ * `resolvePods` calls `install()`, which calls `installPods()` *without*
+ * passing `newArchEnabled` — so the env always gets `RCT_NEW_ARCH_ENABLED
+ * ='0'`, regardless of what the architecture sniffer found. Reanimated 4
+ * .x's podspec asserts on the env var (`ENV['RCT_NEW_ARCH_ENABLED'] !=
+ * '0'`) and aborts the install. Setting the env in Ruby at the top of the
+ * Podfile happens *inside* the same pod-install process the CLI just
+ * spawned with `'0'`, but *before* `use_native_modules!` triggers
+ * `RNReanimated.podspec`, so the override sticks for the rest of the
+ * install — including the `NewArchitectureHelper.new_arch_enabled` read
+ * later that drives `use_react_native!`'s codegen and Info.plist write-
+ * back.
  *
  * Upstream fix that would remove the env injection entirely:
- * https://github.com/react-native-community/cli/pull/2773 — approved by the
- * maintainer but unmerged as of CLI 20.1.3. Once it ships and we adopt it
- * the bait file becomes a harmless one-line scratch file that pod install
- * overwrites unconditionally.
+ * https://github.com/react-native-community/cli/pull/2773 — approved by
+ * the maintainer but unmerged as of CLI 20.1.3. Once it ships and we
+ * adopt it, this override becomes a redundant reassignment of an env var
+ * that's already `'1'` (or unset, which Reanimated treats as on).
  */
-function seedNewArchSnifferBait(iosDir: string): void {
-  const podsXcodeprojDir = resolve(iosDir, 'Pods', 'Pods.xcodeproj');
-  mkdirSync(podsXcodeprojDir, { recursive: true });
-  const pbxprojPath = resolve(podsXcodeprojDir, 'project.pbxproj');
-  if (existsSync(pbxprojPath)) return;
-  writeFileSync(
-    pbxprojPath,
-    '// vitest-mobile new-arch sniffer bait: ensures react-native-community/cli ' +
-      'passes RCT_NEW_ARCH_ENABLED=1 to pod install on the first run. CocoaPods ' +
-      'overwrites this file during pod install, and the regenerated copy carries ' +
-      'the same marker since new arch ends up on.\n' +
-      '// -DRCT_NEW_ARCH_ENABLED=1\n',
-  );
+function injectNewArchEnvOverride(podfile: string): string {
+  const line = "ENV['RCT_NEW_ARCH_ENABLED'] = '1'\n";
+  if (podfile.includes(line)) return podfile;
+  return line + podfile;
 }
 
 /**