diff --git a/.github/scripts/install-openblas.ps1 b/.github/scripts/install-openblas.ps1
new file mode 100644
index 000000000..b253d73c3
--- /dev/null
+++ b/.github/scripts/install-openblas.ps1
@@ -0,0 +1,112 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+param(
+    [string]$InstallPath = "C:\openblas"
+)
+
+$ErrorActionPreference = "Stop"
+# Windows PowerShell 5.1 redraws the progress bar on every read block, which
+# costs an order of magnitude of wall-clock on a download this size.
+$ProgressPreference = "SilentlyContinue"
+Set-StrictMode -Version Latest
+
+# Bumping OpenBLAS means changing $openBlasVersion and every Hash below.
+# Regenerate a hash with: Get-FileHash -Algorithm SHA256 <downloaded zip>
+$openBlasVersion = "0.3.30"
+$packages = @{
+    arm64 = @{
+        Asset        = "woa64-dll"
+        Hash         = "5BBD8C6CA5A4C415FF58D5E18378B35BC1E81F46E6C385753EFF367FF7474819"
+        Subdirectory = "OpenBLAS"
+    }
+    x64   = @{
+        Asset        = "x64"
+        Hash         = "8B04387766EFC05C627E26D24797EC0D4ED4C105EC14FA7400AA84A02DB22B66"
+        Subdirectory = ""
+    }
+}
+
+$nativeArchitectures = @(
+    $env:PROCESSOR_ARCHITECTURE
+    $env:PROCESSOR_ARCHITEW6432
+)
+
+if ($nativeArchitectures -contains "ARM64") {
+    $architecture = "arm64"
+} elseif ($nativeArchitectures -contains "AMD64") {
+    $architecture = "x64"
+} else {
+    throw "Unsupported Windows architecture: $($nativeArchitectures -join ', ')"
+}
+
+$package = $packages[$architecture]
+$archiveUrl = "https://github.com/OpenMathLib/OpenBLAS/releases/download/v$openBlasVersion/OpenBLAS-$openBlasVersion-$($package.Asset).zip"
+$expectedHash = $package.Hash
+$archiveSubdirectory = $package.Subdirectory
+
+$workingPath = Join-Path ([System.IO.Path]::GetTempPath()) "faiss-openblas-$architecture-$PID"
+$archivePath = Join-Path $workingPath "openblas.zip"
+$extractPath = Join-Path $workingPath "extract"
+
+New-Item -ItemType Directory -Path $workingPath | Out-Null
+
+try {
+    # A blip here aborts before-all, losing every interpreter's wheel in this
+    # job. Retrying is safe: the hash check below rejects a partial download.
+    # -UseBasicParsing keeps PS 5.1 off the Internet Explorer parsing engine,
+    # which is absent on freshly provisioned images.
+    for ($attempt = 1; $attempt -le 3; $attempt++) {
+        try {
+            Invoke-WebRequest -Uri $archiveUrl -OutFile $archivePath -UseBasicParsing
+            break
+        } catch {
+            if ($attempt -eq 3) {
+                throw
+            }
+            Start-Sleep -Seconds (5 * $attempt)
+        }
+    }
+
+    $archiveStream = [System.IO.File]::OpenRead($archivePath)
+    try {
+        $hasher = [System.Security.Cryptography.SHA256]::Create()
+        try {
+            $actualHash = [System.BitConverter]::ToString(
+                $hasher.ComputeHash($archiveStream)
+            ).Replace("-", "")
+        } finally {
+            $hasher.Dispose()
+        }
+    } finally {
+        $archiveStream.Dispose()
+    }
+
+    if ($actualHash -ne $expectedHash) {
+        throw "OpenBLAS archive hash mismatch: expected $expectedHash, got $actualHash"
+    }
+
+    Expand-Archive -LiteralPath $archivePath -DestinationPath $extractPath
+    $sourcePath = if ($archiveSubdirectory) {
+        Join-Path $extractPath $archiveSubdirectory
+    } else {
+        $extractPath
+    }
+
+    foreach ($subdirectory in @("bin", "include", "lib")) {
+        if (-not (Test-Path -LiteralPath (Join-Path $sourcePath $subdirectory))) {
+            throw "OpenBLAS archive is missing the '$subdirectory' directory"
+        }
+    }
+
+    if (Test-Path -LiteralPath $InstallPath) {
+        Remove-Item -LiteralPath $InstallPath -Recurse -Force
+    }
+    Move-Item -LiteralPath $sourcePath -Destination $InstallPath
+} finally {
+    if (Test-Path -LiteralPath $workingPath) {
+        Remove-Item -LiteralPath $workingPath -Recurse -Force
+    }
+}
diff --git a/.github/workflows/build-pip.yml b/.github/workflows/build-pip.yml
index e89dd1ee6..d8483d82b 100644
--- a/.github/workflows/build-pip.yml
+++ b/.github/workflows/build-pip.yml
@@ -39,7 +39,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-14, macos-15-intel, windows-2022, 2-core-ubuntu-arm]
+        os: [ubuntu-latest, macos-14, macos-15-intel, windows-2022, windows-11-arm, 2-core-ubuntu-arm]
     steps:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
diff --git a/pyproject.toml b/pyproject.toml
index 1585fc987..384b3bddc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -119,9 +119,11 @@ cmake.define.FAISS_OPT_LEVEL = "generic"
 
 [tool.cibuildwheel]
 # Build all Python versions on Windows (no abi3); cp310 only on Linux/macOS (abi3).
-# Skip 32-bit and free-threaded builds. musllinux is built (see override below).
+# Skip Windows arm64 for Python 3.10 because Python 3.10 is not available as a
+# supported Windows arm64 target. Also skip 32-bit and free-threaded builds.
+# musllinux is built below.
 build = "cp310-* cp311-* cp312-* cp313-* cp314-*"
-skip = "*-win32 *-manylinux_i686 cp3*t-*"
+skip = "cp310-win_arm64 *-win32 *-manylinux_i686 cp3*t-*"
 test-requires = ["numpy", "pytest", "scipy"]
 test-command = "python -m pytest {project}/tests/test_wheel_smoke.py -v"
 
@@ -167,14 +169,26 @@ environment = {MACOSX_DEPLOYMENT_TARGET = "14.0"}
 select = "*-macosx_x86_64"
 environment = {MACOSX_DEPLOYMENT_TARGET = "15.0"}
 
+# Windows arm64: drop scipy for the same reason as musllinux above — the smoke
+# test does not import it, and a missing win_arm64 scipy wheel would force a
+# failing sdist build (needs a Fortran toolchain and a BLAS on the runner).
+[[tool.cibuildwheel.overrides]]
+select = "*-win_arm64"
+test-requires = ["numpy", "pytest"]
+
 [tool.cibuildwheel.windows]
-# Install prebuilt OpenBLAS (statically-linked MinGW runtime, no external deps).
-before-all = "powershell -Command \"Invoke-WebRequest -Uri 'https://github.com/OpenMathLib/OpenBLAS/releases/download/v0.3.30/OpenBLAS-0.3.30-x64.zip' -OutFile openblas.zip; Expand-Archive openblas.zip -DestinationPath C:/openblas -Force\""
+# Install the native x64 or arm64 OpenBLAS package for the runner.
+# delvewheel only has to vendor the OpenBLAS DLL itself, because the x64 package
+# links the MinGW runtime statically. Re-check that property when bumping the
+# OpenBLAS version or adding an architecture: `delvewheel show` on a repaired
+# wheel lists what was vendored, and the PATH below hides a missed DLL from the
+# smoke test, so a wheel broken this way still passes CI.
+before-all = 'powershell -NoProfile -ExecutionPolicy Bypass -File "{package}\.github\scripts\install-openblas.ps1"'
 repair-wheel-command = "pip install delvewheel && delvewheel repair -w {dest_dir} {wheel} --add-path C:/openblas/bin --ignore-in-wheel"
 
 [tool.cibuildwheel.windows.environment]
 # BLAS_ROOT tells CMake's FindBLAS (via CMP0074) where to find OpenBLAS.
-# PATH includes the bin/ dir so delvewheel and tests can find libopenblas.dll.
+# PATH includes the bin/ dir so delvewheel and tests can find the OpenBLAS DLL.
 BLAS_ROOT = "C:/openblas"
 LAPACK_ROOT = "C:/openblas"
 PATH = "C:/openblas/bin;$PATH"