diff --git a/scripts/build-ghostty-cli-helper.sh b/scripts/build-ghostty-cli-helper.sh
index e6cd0f20af43..64d68d98f3d0 100755
--- a/scripts/build-ghostty-cli-helper.sh
+++ b/scripts/build-ghostty-cli-helper.sh
@@ -10,6 +10,12 @@ Options:
   --target <triple>
                    Build a single target, e.g. `aarch64-macos` or `x86_64-macos`.
   --output <path>  Destination path for the built helper.
+
+Environment:
+  CMUX_GHOSTTY_HELPER_CACHE_DIR
+                   Override the local helper cache directory.
+  CMUX_DISABLE_GHOSTTY_HELPER_CACHE=1
+                   Disable cache reads and writes for this invocation.
 EOF
 }
 
@@ -24,6 +30,14 @@ ZIG_REQUIRED="${ZIG_REQUIRED:-$(ghostty_minimum_zig_version "$REPO_ROOT")}"
 OUTPUT_PATH=""
 TARGET_TRIPLE=""
 UNIVERSAL="false"
+if [[ -n "${CMUX_GHOSTTY_HELPER_CACHE_DIR:-}" ]]; then
+  CACHE_ROOT="$CMUX_GHOSTTY_HELPER_CACHE_DIR"
+elif [[ -n "${HOME:-}" ]]; then
+  CACHE_ROOT="$HOME/Library/Caches/cmux/ghostty-cli-helper"
+else
+  CACHE_ROOT=""
+fi
+CACHE_SCHEMA="ghostty-cli-helper-cache-v1"
 
 zig_binary_arch() {
   local zig_path="$1"
@@ -37,6 +51,78 @@ target_arch_for_triple() {
   esac
 }
 
+ghostty_cache_is_safe() {
+  [[ -n "$CACHE_ROOT" ]] || return 1
+  [[ "${CMUX_DISABLE_GHOSTTY_HELPER_CACHE:-0}" != "1" ]] || return 1
+  [[ -d "$GHOSTTY_DIR/.git" || -f "$GHOSTTY_DIR/.git" ]] || return 1
+  # A dirty or caller-owned Ghostty tree must never be substituted by a
+  # revision-only cache entry. Ignored Zig build output is intentionally fine.
+  git -C "$GHOSTTY_DIR" diff --quiet HEAD -- . || return 1
+  [[ -z "$(git -C "$GHOSTTY_DIR" ls-files --others --exclude-standard)" ]] || return 1
+  return 0
+}
+
+ghostty_cache_metadata() {
+  local zig_bin="$1"
+  local target="$2"
+  local effective_target="$3"
+  local zig_version zig_fingerprint ghostty_sha script_sha sdk_version host_version host_arch
+  zig_version="$($zig_bin version 2>/dev/null || true)"
+  zig_fingerprint="$(shasum -a 256 "$zig_bin" 2>/dev/null | awk '{print $1}')"
+  ghostty_sha="$(git -C "$GHOSTTY_DIR" rev-parse HEAD)"
+  script_sha="$(shasum -a 256 "$SCRIPT_DIR/build-ghostty-cli-helper.sh" | awk '{print $1}')"
+  sdk_version="$(xcrun --sdk macosx --show-sdk-version 2>/dev/null || echo unknown)"
+  host_version="$(sw_vers -productVersion 2>/dev/null || echo unknown)"
+  host_arch="$(uname -m)"
+  cat <<EOF
+$CACHE_SCHEMA
+ghostty=$ghostty_sha
+script=$script_sha
+zig_version=$zig_version
+zig_sha256=$zig_fingerprint
+requested_target=${target:-native}
+effective_target=${effective_target:-native}
+sdk=$sdk_version
+macos=$host_version
+host_arch=$host_arch
+EOF
+}
+
+ghostty_cache_install_if_valid() {
+  local cache_bin="$1"
+  local cache_manifest="$2"
+  local metadata="$3"
+  local prefix="$4"
+  local cached_metadata cached_sha expected_sha
+  [[ -x "$cache_bin" && -f "$cache_manifest" ]] || return 1
+  cached_metadata="$(sed '/^binary_sha256=/d' "$cache_manifest" 2>/dev/null || true)"
+  [[ "$cached_metadata" == "$metadata" ]] || return 1
+  cached_sha="$(sed -n 's/^binary_sha256=//p' "$cache_manifest" 2>/dev/null || true)"
+  expected_sha="$(shasum -a 256 "$cache_bin" 2>/dev/null | awk '{print $1}')"
+  [[ -n "$cached_sha" && "$cached_sha" == "$expected_sha" ]] || return 1
+  mkdir -p "$prefix/bin"
+  install -m 755 "$cache_bin" "$prefix/bin/ghostty"
+  echo "Reusing cached Ghostty CLI helper"
+  return 0
+}
+
+ghostty_cache_publish() {
+  local cache_dir="$1"
+  local metadata="$2"
+  local binary="$3"
+  local cache_bin="$cache_dir/ghostty"
+  local cache_manifest="$cache_dir/manifest"
+  local tmp_binary="$cache_dir/.ghostty.tmp.$$"
+  local tmp_manifest="$cache_dir/.manifest.tmp.$$"
+  local binary_sha
+  mkdir -p "$cache_dir"
+  install -m 755 "$binary" "$tmp_binary"
+  mv -f "$tmp_binary" "$cache_bin"
+  binary_sha="$(shasum -a 256 "$cache_bin" | awk '{print $1}')"
+  printf '%s\nbinary_sha256=%s' "$metadata" "$binary_sha" > "$tmp_manifest"
+  mv -f "$tmp_manifest" "$cache_manifest"
+}
+
 # Real host arch, accounting for Rosetta where `uname -m` reports x86_64 on
 # Apple Silicon. Used so the default single-arch stub targets the true host.
 detected_host_arch() {
@@ -253,6 +339,21 @@ build_helper() {
     effective_target=""
   fi
 
+  local cache_enabled=0
+  local cache_dir=""
+  local cache_metadata=""
+  if ghostty_cache_is_safe; then
+    cache_enabled=1
+    cache_metadata="$(ghostty_cache_metadata "$zig_bin" "$target" "$effective_target")"
+    local cache_key
+    cache_key="$(printf '%s' "$cache_metadata" | shasum -a 256 | awk '{print $1}')"
+    cache_dir="$CACHE_ROOT/$cache_key"
+    if ghostty_cache_install_if_valid \
+      "$cache_dir/ghostty" "$cache_dir/manifest" "$cache_metadata" "$prefix"; then
+      return 0
+    fi
+  fi
+
   local args=(
     "$zig_bin"
     build
@@ -278,6 +379,16 @@ build_helper() {
     # leaves build-runner binaries unlinked against libSystem on a cold cache.
     env -u SDKROOT "${args[@]}"
   )
+
+  [[ -x "$prefix/bin/ghostty" ]] || {
+    echo "error: Zig did not produce a Ghostty CLI helper at $prefix/bin/ghostty" >&2
+    return 1
+  }
+  if [[ "$cache_enabled" -eq 1 ]]; then
+    if ! ghostty_cache_publish "$cache_dir" "$cache_metadata" "$prefix/bin/ghostty"; then
+      echo "warning: unable to publish Ghostty CLI helper cache; continuing with built helper" >&2
+    fi
+  fi
 }
 
 TMP_DIR="$(mktemp -d "${TMPDIR:-/tmp}/cmux-ghostty-helper.XXXXXX")"
diff --git a/tests/test_ghostty_cli_helper_cache.sh b/tests/test_ghostty_cli_helper_cache.sh
new file mode 100755
index 000000000000..a88c1a20cc3d
--- /dev/null
+++ b/tests/test_ghostty_cli_helper_cache.sh
@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+TMP_DIR="$(mktemp -d "${TMPDIR:-/tmp}/cmux-ghostty-helper-cache-test.XXXXXX")"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+FAKE_ZIG="$TMP_DIR/zig"
+cat > "$FAKE_ZIG" <<'EOF'
+#!/usr/bin/env bash
+set -euo pipefail
+if [[ "${1:-}" == "version" ]]; then
+  echo "0.16.0"
+  exit 0
+fi
+if [[ "${1:-}" == "build" ]]; then
+  prefix=""
+  previous=""
+  for arg in "$@"; do
+    if [[ "$previous" == "--prefix" ]]; then
+      prefix="$arg"
+      break
+    fi
+    previous="$arg"
+  done
+  [[ -n "$prefix" ]] || { echo "missing --prefix" >&2; exit 1; }
+  mkdir -p "$prefix/bin"
+  printf '#!/usr/bin/env bash\necho fake ghostty helper\n' > "$prefix/bin/ghostty"
+  chmod +x "$prefix/bin/ghostty"
+  exit 0
+fi
+echo "unsupported fake zig invocation" >&2
+exit 1
+EOF
+chmod +x "$FAKE_ZIG"
+
+CACHE_DIR="$TMP_DIR/cache"
+FIRST="$TMP_DIR/first"
+SECOND="$TMP_DIR/second"
+THIRD="$TMP_DIR/third"
+FOURTH="$TMP_DIR/fourth"
+FIFTH="$TMP_DIR/fifth"
+SIXTH="$TMP_DIR/sixth"
+
+CMUX_ZIG="$FAKE_ZIG" \
+CMUX_GHOSTTY_HELPER_CACHE_DIR="$CACHE_DIR" \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$FIRST" >"$TMP_DIR/first.log"
+CMUX_ZIG="$FAKE_ZIG" \
+CMUX_GHOSTTY_HELPER_CACHE_DIR="$CACHE_DIR" \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$SECOND" >"$TMP_DIR/second.log"
+
+grep -q 'Building Ghostty CLI helper' "$TMP_DIR/first.log"
+grep -q 'Reusing cached Ghostty CLI helper' "$TMP_DIR/second.log"
+cmp -s "$FIRST" "$SECOND"
+
+cached_helper="$(find "$CACHE_DIR" -type f -name ghostty -print -quit)"
+[[ -n "$cached_helper" ]]
+printf 'tampered\n' >> "$cached_helper"
+CMUX_ZIG="$FAKE_ZIG" \
+CMUX_GHOSTTY_HELPER_CACHE_DIR="$CACHE_DIR" \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$FOURTH" >"$TMP_DIR/fourth.log"
+grep -q 'Building Ghostty CLI helper' "$TMP_DIR/fourth.log"
+cmp -s "$FIRST" "$FOURTH"
+
+CMUX_ZIG="$FAKE_ZIG" \
+CMUX_GHOSTTY_HELPER_CACHE_DIR="$CACHE_DIR" \
+CMUX_DISABLE_GHOSTTY_HELPER_CACHE=1 \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$THIRD" >"$TMP_DIR/third.log"
+grep -q 'Building Ghostty CLI helper' "$TMP_DIR/third.log"
+cmp -s "$FIRST" "$THIRD"
+
+env -u HOME -u CMUX_GHOSTTY_HELPER_CACHE_DIR \
+  CMUX_ZIG="$FAKE_ZIG" \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$FIFTH" >"$TMP_DIR/fifth.log"
+env -u HOME -u CMUX_GHOSTTY_HELPER_CACHE_DIR \
+  CMUX_ZIG="$FAKE_ZIG" \
+  "$ROOT_DIR/scripts/build-ghostty-cli-helper.sh" \
+  --target aarch64-macos --output "$SIXTH" >"$TMP_DIR/sixth.log"
+grep -q 'Building Ghostty CLI helper' "$TMP_DIR/fifth.log"
+grep -q 'Building Ghostty CLI helper' "$TMP_DIR/sixth.log"
+cmp -s "$FIFTH" "$SIXTH"
+
+echo "PASS: Ghostty CLI helper cache reuses matching builds, rejects tampering, and disables safely"
diff --git a/tests/test_ghostty_zig_version_sync.sh b/tests/test_ghostty_zig_version_sync.sh
index e368e6b71aa4..c63bef53e217 100755
--- a/tests/test_ghostty_zig_version_sync.sh
+++ b/tests/test_ghostty_zig_version_sync.sh
@@ -69,6 +69,8 @@ python3 \
   --require-setup-zig \
   "$ROOT_DIR/.github/workflows"
 
+"$ROOT_DIR/tests/test_ghostty_cli_helper_cache.sh"
+
 if ! grep -Fq 'source "$SCRIPT_DIR/ghostty-zig-version.sh"' "$ROOT_DIR/scripts/setup.sh" ||
    ! grep -Fq 'ghostty_minimum_zig_version "$PROJECT_DIR"' "$ROOT_DIR/scripts/setup.sh" ||
    ! grep -Fq 'ZIG_ACTUAL="$(zig version)"' "$ROOT_DIR/scripts/setup.sh" ||