diff --git a/scripts/bootstrap.ps1 b/scripts/bootstrap.ps1
index 42776496a344..85ef3d4ef671 100755
--- a/scripts/bootstrap.ps1
+++ b/scripts/bootstrap.ps1
@@ -665,6 +665,7 @@ function Install-Buildkite {
 
 function Optimize-System {
   Disable-Windows-Defender
+  Disable-Smart-App-Control
   Disable-Windows-Threat-Protection
   Disable-Windows-Services
   Disable-Power-Management
@@ -680,6 +681,24 @@ function Disable-Windows-Defender {
   Add-MpPreference -ExclusionPath "C:\", "D:\"
 }
 
+# Windows 11 ships Smart App Control in evaluation mode (Server has no such
+# policy). It hashes every unsigned executable on its first launch and asks the
+# cloud for its reputation: 2 to 3.5 seconds per `bun build --compile` output,
+# which the compile test suites launch by the dozen. Defender exclusions do not
+# cover it, and tamper protection does not guard this key. The change takes
+# effect after `CiTool --refresh` or a reboot, and cannot be undone without a
+# reinstall, which is fine for a CI image.
+function Disable-Smart-App-Control {
+  $itemPath = "HKLM:\SYSTEM\CurrentControlSet\Control\CI\Policy"
+  if (Test-Path $itemPath) {
+    Write-Output "Disabling Smart App Control..."
+    Set-ItemProperty -Path $itemPath -Name "VerifiedAndReputablePolicyState" -Value 0 -Type DWORD
+    if (Get-Command CiTool -ErrorAction SilentlyContinue) {
+      CiTool --refresh -json | Out-Null
+    }
+  }
+}
+
 function Disable-Windows-Threat-Protection {
   $itemPath = "HKLM:\SOFTWARE\Policies\Microsoft\Windows Advanced Threat Protection"
   if (Test-Path $itemPath) {
diff --git a/scripts/runner.node.mjs b/scripts/runner.node.mjs
index 1ef7223d7010..5bc184cc45cd 100755
--- a/scripts/runner.node.mjs
+++ b/scripts/runner.node.mjs
@@ -3494,6 +3494,39 @@ function escapeXml(str) {
     .replace(/'/g, "'");
 }
 
+/**
+ * Windows 11 ships Smart App Control in evaluation mode. In that mode the kernel
+ * hashes every unsigned executable on its first launch and asks the cloud for
+ * its reputation, which costs 2 to 3.5 seconds for a 77 MB `bun build --compile`
+ * output. bundler_compile.test.ts launches about 85 of those, which puts the file
+ * at 220 to 290 seconds against the 300 second per-file cap. Turning the policy
+ * off takes effect at once and needs no reboot. scripts/bootstrap.ps1 does the
+ * same at image bake time; this covers images baked before that change.
+ *
+ * Only on Buildkite: the policy cannot be turned on again without a reinstall,
+ * so a developer's machine running with CI=true must not get this.
+ */
+async function disableSmartAppControl() {
+  if (!isBuildkite) return;
+  const script = [
+    "$p = 'HKLM:\\SYSTEM\\CurrentControlSet\\Control\\CI\\Policy'",
+    "if (-not (Test-Path $p)) { exit 0 }",
+    "$state = (Get-ItemProperty $p).VerifiedAndReputablePolicyState",
+    "if ($null -eq $state -or $state -eq 0) { exit 0 }",
+    "Set-ItemProperty $p -Name VerifiedAndReputablePolicyState -Value 0 -Type DWord",
+    "if (Get-Command CiTool -ErrorAction SilentlyContinue) { CiTool --refresh -json | Out-Null }",
+    'Write-Output "Smart App Control: state $state -> 0"',
+  ].join("; ");
+  const { ok, error } = await spawnSafe({
+    command: "pwsh",
+    args: ["-NoProfile", "-Command", script],
+    timeout: 60_000,
+  });
+  if (!ok) {
+    console.warn(`Failed to disable Smart App Control: ${error}`);
+  }
+}
+
 export async function main() {
   for (const signal of ["SIGINT", "SIGTERM", "SIGHUP"]) {
     process.on(signal, () => onExit(signal));
@@ -3511,6 +3544,7 @@ export async function main() {
       "-Command",
       "Set-DnsClientServerAddress -InterfaceAlias 'Ethernet 4' -ServerAddresses ('8.8.8.8','8.8.4.4')",
     ]);
+    await disableSmartAppControl();
   }
 
   let doRunTests = true;