diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index af94bdc..8c0ace4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,6 +76,7 @@ jobs:
         with:
           swift-version: ${{ matrix.swift }}
           windows-toolchain-variant: noasserts
+          windows-minimal: true
       - name: Check the +NoAsserts toolchain was selected, and compile
         env:
           VERSION: ${{ steps.setup.outputs.version }}
diff --git a/README.md b/README.md
index d11f864..4620ec7 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,8 @@ see [How verification works](#how-verification-works)). It never runs a pre-exis
 | `swift-sdks` | no | | Cross-compilation Swift SDKs to install after the toolchain: `static-linux`, `wasm`, `android` (comma or space separated). |
 | `use-preinstalled` | no | `false` | **Unverified opt-in.** If `swift` on `PATH` already reports exactly `swift-version`, run and use it instead of installing. By default no pre-existing binary is ever executed. |
 | `windows-toolchain-variant` | no | `asserts` | Windows only. `asserts` keeps the installer's default `+Asserts` toolchain; `noasserts` installs the `+NoAsserts` one instead. Use `noasserts` on win-arm64, where the `+Asserts` `swift-package.exe` fails to start ([swiftlang/swift#92379](https://github.com/swiftlang/swift/issues/92379)). |
-| `cache` | no | `true` | Cache the downloaded Linux toolchain archive and its `.sig` with `actions/cache`. The archive is re-verified with GPG on every run and extracted into a clean per-version directory; `false` reuses nothing on disk. |
+| `windows-minimal` | no | `false` | Windows only. `true` leaves out what a CI build does not use: the debugger (`OptionsInstallDBG`), its embedded Python (`OptionsInstallPy`) and the Android platform (`OptionsInstallAndroidPlatform`). The IDE feature stays: without it `swift.exe` fails to start (`ERROR_SXS_CANT_GEN_ACTCTX`). |
+| `cache` | no | `true` | Cache the downloaded Linux toolchain archive and its `.sig` with `actions/cache`. The archive is re-verified with GPG on every run and extracted into a clean per-version directory; `false` reuses nothing on disk. The macOS `.pkg` and the Windows installer are not cached: restoring them from the Actions cache measured slower than downloading them from swift.org. |
 
 ## Outputs
 
@@ -60,7 +61,7 @@ A cache entry that fails verification fails the job instead of being re-download
 `RUNNER_TEMP` is private to one runner instance and emptied for every job on GitHub-hosted runners, so earlier or
 concurrent jobs cannot plant or wipe the toolchain. Self-hosted runners must not share `RUNNER_TEMP` between
 concurrently running jobs, and must run jobs of different trust levels on separate runner instances. Missing build prerequisites (`libcurl4-openssl-dev`,
-`libxml2-dev`, the GCC dev packages, ...) are installed with `apt-get` only if absent.
+`libxml2-dev`, the GCC dev packages, ...) are installed with `apt-get` only if absent - from the package lists the runner image ships, refreshed only if that fails, and, apart from `curl` and `gnupg2`, in the background while the archive is fetched, verified and extracted. The archive is extracted with `pigz` when the runner has it.
 
 macOS: the package is installed into the user domain (`~/Library/Developer/Toolchains`), falling back to
 `sudo installer -target /`. `TOOLCHAINS` is exported with the toolchain's bundle identifier and its
diff --git a/action.yml b/action.yml
index fe46e25..4fe4eb6 100644
--- a/action.yml
+++ b/action.yml
@@ -26,10 +26,19 @@ inputs:
       (https://github.com/swiftlang/swift/issues/92379); the +NoAsserts one does not.
     required: false
     default: "asserts"
+  windows-minimal:
+    description: >-
+      Windows only: leave out what a CI build does not use - the debugger, its embedded Python and the
+      Android platform. Shortens the install; default false installs everything the installer
+      installs by default.
+    required: false
+    default: "false"
   cache:
     description: >-
       Cache the downloaded Linux toolchain archive and its signature with actions/cache. The archive is
-      re-verified with GPG on every run; with false nothing on disk is ever reused.
+      re-verified with GPG on every run; with false nothing on disk is ever reused. The macOS .pkg and
+      the Windows installer are not cached: restoring them from the Actions cache measured slower than
+      downloading them from swift.org.
     required: false
     default: "true"
 outputs:
@@ -111,6 +120,7 @@ runs:
       env:
         SWIFT_VERSION: ${{ inputs.swift-version }}
         WINDOWS_TOOLCHAIN_VARIANT: ${{ inputs.windows-toolchain-variant }}
+        WINDOWS_MINIMAL: ${{ inputs.windows-minimal }}
       run: '& "$env:GITHUB_ACTION_PATH/install-windows.ps1"'
 
     - name: Report Swift version
diff --git a/install-linux.sh b/install-linux.sh
index 55c9d5a..e540fdb 100755
--- a/install-linux.sh
+++ b/install-linux.sh
@@ -31,15 +31,37 @@ for pkg in curl gnupg2 binutils git libcurl4-openssl-dev libedit2 libsqlite3-0 l
   libncurses-dev pkg-config tzdata uuid-dev zlib1g-dev "libgcc-${gcc_ver}-dev" "libstdc++-${gcc_ver}-dev"; do
   dpkg -s "$pkg" > /dev/null 2>&1 || missing+=("$pkg")
 done
-if [ "${#missing[@]}" -gt 0 ]; then
-  echo "Installing missing packages: ${missing[*]}"
-  "${sudo_cmd[@]}" apt-get update -qq
-  "${sudo_cmd[@]}" env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq --no-install-recommends "${missing[@]}"
+# The package lists a runner image ships are tried first, and refreshed only when that fails: the
+# refresh is most of what installing a couple of packages costs.
+apt_install() {
+  "${sudo_cmd[@]}" env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq --no-install-recommends "$@" \
+    || { "${sudo_cmd[@]}" apt-get update -qq \
+      && "${sudo_cmd[@]}" env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq --no-install-recommends "$@"; }
+}
+
+# curl and gnupg2 download and verify the toolchain, so they have to be there first. Everything else
+# is needed only to run it, and is installed in the background while the archive is fetched,
+# verified and extracted, then waited for at the end.
+needed_now=()
+later=()
+for pkg in "${missing[@]}"; do
+  case "$pkg" in curl | gnupg2) needed_now+=("$pkg") ;; *) later+=("$pkg") ;; esac
+done
+if [ "${#needed_now[@]}" -gt 0 ]; then
+  echo "Installing missing packages: ${needed_now[*]}"
+  apt_install "${needed_now[@]}"
 fi
 
 scratch="$(mktemp -d "${RUNNER_TEMP:-/tmp}/setup-swift.XXXXXX")"
 trap 'rm -r -f "$scratch"' EXIT
 
+apt_pid=""
+if [ "${#later[@]}" -gt 0 ]; then
+  echo "Installing missing packages in the background: ${later[*]}"
+  apt_install "${later[@]}" > "$scratch/apt.log" 2>&1 &
+  apt_pid=$!
+fi
+
 download() { # url dest
   curl --fail --silent --show-error --location --retry 5 --retry-delay 5 --retry-all-errors \
     --connect-timeout 30 --output "$2" "$1" \
@@ -107,9 +129,20 @@ assert_no_symlinks "$dest"
 rm -r -f -- "$dest"
 mkdir "$dest"
 assert_no_symlinks "$dest"
-tar -xzf "$snap/$file" -C "$dest" --strip-components=1 --no-same-owner
+# pigz where the runner has it: inflation stays single-threaded, but pigz reads, writes and
+# checksums on threads of its own.
+if command -v pigz > /dev/null; then
+  tar -I pigz -xf "$snap/$file" -C "$dest" --strip-components=1 --no-same-owner
+else
+  tar -xzf "$snap/$file" -C "$dest" --strip-components=1 --no-same-owner
+fi
 rm -r -f -- "$snap"
 [ -x "$dest/usr/bin/swift" ] || { echo "::error::$dest/usr/bin/swift is missing after extraction"; exit 1; }
+if [ -n "$apt_pid" ] && ! wait "$apt_pid"; then
+  cat "$scratch/apt.log"
+  echo "::error::Installing the packages the toolchain needs failed: ${later[*]}"
+  exit 1
+fi
 if [ -n "${GITHUB_PATH:-}" ]; then echo "$dest/usr/bin" >> "$GITHUB_PATH"; fi
 if [ -n "${GITHUB_OUTPUT:-}" ]; then echo "source=$source" >> "$GITHUB_OUTPUT"; fi
 echo "Installed Swift toolchain at $dest"
diff --git a/install-windows.ps1 b/install-windows.ps1
index 207829f..67d5f2d 100644
--- a/install-windows.ps1
+++ b/install-windows.ps1
@@ -17,6 +17,16 @@ switch ($variant) {
   }
   default { Write-Host "::error::windows-toolchain-variant must be asserts or noasserts, got '$variant'"; exit 1 }
 }
+# windows-minimal: the installer features a CI build does not use - the debugger, its Python and the
+# Android platform, a second SDK. Not the IDE feature: without it swift.exe fails to start with
+# ERROR_SXS_CANT_GEN_ACTCTX (14001), measured on 6.4.1 with each feature left out on its own.
+switch ($env:WINDOWS_MINIMAL) {
+  { $_ -in @('', 'false') } { }
+  'true' {
+    $installerOptions += @('OptionsInstallDBG=0', 'OptionsInstallPy=0', 'OptionsInstallAndroidPlatform=0')
+  }
+  default { Write-Host "::error::windows-minimal must be true or false, got '$env:WINDOWS_MINIMAL'"; exit 1 }
+}
 # Publisher the installer must be signed by, see README.md. swift.org's Windows installers are signed
 # with an Apple Inc. certificate whose OU (an Apple internal group id) is deliberately not pinned.
 $ExpectedSubject = '^CN=Apple Inc\., (OU=[^,]+, )?O=Apple Inc\., L=Cupertino, S=California, C=US$'