diff --git a/.gitignore b/.gitignore
index 0e35105..2552fbb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 out/
 src/
 depot_tools/
+.fortress-build/
 *.tar.gz
 *.deb
 *.AppImage
diff --git a/build/apply-patches.sh b/build/apply-patches.sh
index 8bcfbee..7316814 100755
--- a/build/apply-patches.sh
+++ b/build/apply-patches.sh
@@ -13,9 +13,9 @@ ok=0; fail=0; failed=()
 while IFS= read -r rel; do
   [ -z "$rel" ] && continue
   p="$REPO/$rel"
-  if git apply --3way --whitespace=nowarn "$p" 2>/dev/null; then
+  if git apply --recount --3way --whitespace=nowarn "$p" 2>/dev/null; then
     ok=$((ok+1)); printf '  [ok]   %s\n' "$(basename "$rel")"
-  elif git apply --check "$p" 2>/dev/null && git apply --whitespace=nowarn "$p" 2>/dev/null; then
+  elif git apply --recount --check "$p" 2>/dev/null && git apply --recount --whitespace=nowarn "$p" 2>/dev/null; then
     ok=$((ok+1)); printf '  [ok]   %s\n' "$(basename "$rel")"
   else
     fail=$((fail+1)); failed+=("$rel"); printf '  [FAIL] %s\n' "$(basename "$rel")"
diff --git a/build/args.arm64.gn b/build/args.arm64.gn
new file mode 100644
index 0000000..8197719
--- /dev/null
+++ b/build/args.arm64.gn
@@ -0,0 +1,50 @@
+# Fortress — official, max-stealth Chromium build args (GN) for linux/arm64.
+# Used by build/build.sh on aarch64 hosts:
+#   gn gen out/Fortress --args="$(cat build/args.arm64.gn)"
+#
+# This is the arm64 sibling of build/args.gn. Every stealth-relevant knob is
+# IDENTICAL to the x64 file — the ONLY differences are architecture-bound:
+#   1. target_cpu = "arm64"   (was "x64")
+#   2. no x86 extra_cflags     (the SSE/AVX baseline block below is x86-only)
+# All 34 C++ stealth patches are architecture-neutral (JS fingerprint surfaces:
+# navigator/screen/canvas/webgl/webaudio/webrtc/timezone/fonts) and apply as-is.
+
+# Official, optimized, single-binary (NOT a component/dev build).
+is_official_build = true
+is_component_build = false
+is_debug = false
+dcheck_always_on = false
+
+# Stripped — no symbols (smaller, fewer tells).
+symbol_level = 0
+blink_symbol_level = 0
+
+# Real media: proprietary codecs + Chrome ffmpeg branding so canPlayType('video/mp4')
+# returns "probably" (stock Chromium returns "" — a headless tell).
+proprietary_codecs = true
+ffmpeg_branding = "Chrome"
+
+# De-brand: build as Chromium (no Google branding); the consumer "Google Chrome"
+# identity is applied at runtime via --uxr-* switches, not baked in.
+is_chrome_branded = false
+
+# No PGO profile dependency (we build from source without Google's PGO data).
+chrome_pgo_phase = 0
+
+# Trim weight / attack surface.
+enable_nacl = false
+enable_widevine = false
+
+# Target: native linux/arm64 (aarch64). Runs under Lima/QEMU on Apple Silicon.
+target_cpu = "arm64"
+target_os = "linux"
+
+# Broad-CPU compatibility: N/A on arm64.
+# The x64 args.gn pins the tree back to the SSE4.2 (x86-64-v2) baseline via
+# -mno-avx/-mno-bmi/-mno-lzcnt/... to keep pre-Haswell Intel CPUs from tripping a
+# PA_CHECK at static init. Those are x86-only flags (clang errors on them for
+# aarch64) and the failure mode doesn't exist on ARM. Chromium's default arm64
+# baseline is ARMv8-A, already the broadest target — Apple M-series (ARMv8.5+/v9)
+# and QEMU's cortex-a/max models are all supersets — so NO extra_cflags are needed.
+
+# ThinLTO is on by default for official builds; left implicit.
diff --git a/build/build-arm64.sh b/build/build-arm64.sh
new file mode 100755
index 0000000..7c8dcad
--- /dev/null
+++ b/build/build-arm64.sh
@@ -0,0 +1,175 @@
+#!/usr/bin/env bash
+# Fortress — native linux/arm64 (aarch64) build.
+#
+# Chromium ships NO prebuilt aarch64-linux clang or rust, so a native arm64 build
+# must build the clang toolchain from source and supply an arm64 rust. This script
+# encodes every arm64-specific step so the max-stealth Fortress Chromium (all 34+
+# C++ patches, unchanged) can be reproduced on an aarch64 host (e.g. AWS Graviton,
+# or a Linux arm64 VM for running under Lima/QEMU on Apple Silicon).
+#
+# Requirements: aarch64 Ubuntu 22.04/24.04 host, ~200 GB free disk, many cores,
+# passwordless sudo (for apt). Usage:  build/build-arm64.sh [workdir]
+#
+# The stealth C++ patches are architecture-neutral (JS fingerprint surfaces) and
+# apply unchanged; only the toolchain/build plumbing below is arm64-specific.
+set -euo pipefail
+REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+WORK="${1:-$REPO/.fortress-build}"
+VER="${CHROMIUM_VERSION:-$(cat "$REPO/CHROMIUM_VERSION")}"
+OUT="Fortress"
+# Rust nightly matching the DATE of Chromium's pinned rust commit (tools/rust/update_rust.py).
+# For Chromium 151.0.7908.0 that commit is dated 2026-06-16 -> nightly-2026-06-17.
+RUST_DATE="${RUST_DATE:-2026-06-17}"
+RUST_TC="$HOME/.rustup/toolchains/nightly-${RUST_DATE}-aarch64-unknown-linux-gnu"
+export TMPDIR="${TMPDIR:-$WORK/tmp}"
+mkdir -p "$WORK" "$TMPDIR"
+export GCLIENT_SUPPRESS_GIT_VERSION_WARNING=1
+ts(){ date -u +%H:%M:%S; }
+[ "$(uname -m)" = "aarch64" ] || { echo "This script is for aarch64 hosts."; exit 1; }
+echo "==> Fortress arm64 build | Chromium $VER | workdir $WORK"
+
+# 0. Host packages: toolchain build prerequisites. The target libraries come from
+#    Chromium's arm64 sysroot (installed below), so the -dev libs here are only
+#    belt-and-suspenders for host tools; harmless to keep.
+echo "[$(ts)] apt prerequisites"
+sudo apt-get update -y
+sudo apt-get install -y \
+  cmake ninja-build lld gperf libclang-dev curl xz-utils python3 git pkg-config \
+  libpipewire-0.3-dev libva-dev libgbm-dev libdrm-dev libpulse-dev libspeechd-dev \
+  libxkbcommon-dev libxdamage-dev libxrandr-dev libxcomposite-dev libxcursor-dev \
+  libxtst-dev libxss-dev libcups2-dev libgtk-3-dev libnss3-dev libasound2-dev \
+  libatk1.0-dev libatk-bridge2.0-dev libpango1.0-dev libcairo2-dev libatspi2.0-dev \
+  libdbus-1-dev libudev-dev libwayland-dev libglib2.0-dev libkrb5-dev libncurses-dev \
+  libxshmfence-dev libx11-xcb-dev libxcb-dri3-dev
+
+# 1. depot_tools
+if [ ! -d "$WORK/depot_tools" ]; then
+  git clone --depth 1 https://chromium.googlesource.com/chromium/tools/depot_tools.git "$WORK/depot_tools"
+fi
+export PATH="$WORK/depot_tools:$HOME/.cargo/bin:$PATH"
+
+# 2. fetch Chromium + sync (with the arm64 workarounds)
+if [ ! -d "$WORK/chromium/src" ]; then
+  mkdir -p "$WORK/chromium"
+  # `fetch` runs an internal `gclient sync` that aborts on the gperf CIPD gap
+  # (there is no linux-arm64 gperf package). That abort is expected and harmless
+  # here: fetch has already checked out src/ + DEPS by the time cipd runs, which is
+  # all we need before we patch DEPS and run our own sync below. Tolerate the exit.
+  ( cd "$WORK/chromium" && fetch --nohooks --no-history chromium ) || true
+  [ -f "$WORK/chromium/src/DEPS" ] || { echo "fetch did not lay down src/DEPS"; exit 1; }
+fi
+# Unmanaged solution so gclient won't reset our tag checkout / DEPS edit below.
+cat > "$WORK/chromium/.gclient" <<'GC'
+solutions = [
+  { "name": "src",
+    "url": "https://chromium.googlesource.com/chromium/src.git",
+    "managed": False, "custom_deps": {}, "custom_vars": {} },
+]
+GC
+cd "$WORK/chromium/src"
+git fetch --depth 1 origin "refs/tags/$VER:refs/tags/$VER"
+git checkout -f "tags/$VER"
+# gperf has NO linux-arm64 CIPD package (only linux-amd64), which aborts `gclient sync`.
+# Point the dep at linux-amd64 so cipd resolves; we overwrite it with native arm64 gperf.
+python3 - <<'PY'
+p="DEPS"; s=open(p).read()
+o="infra/3pp/tools/gperf/${{platform}}"; n="infra/3pp/tools/gperf/linux-amd64"
+open(p,"w").write(s.replace(o,n)) if o in s else None
+PY
+# gclient sync pulls hundreds of git/CIPD deps and can hit transient network
+# failures (busy mirrors, HTTP 429 rate limiting). Retry with backoff; each retry
+# resumes where the last left off, so only the incomplete deps are re-fetched.
+for attempt in 1 2 3 4 5; do
+  gclient sync -D --no-history && break
+  [ "$attempt" = 5 ] && { echo "gclient sync failed after 5 attempts"; exit 1; }
+  echo "[$(ts)] gclient sync attempt $attempt failed (transient?); retrying in $((attempt*30))s"
+  sleep $((attempt*30))
+done
+gclient runhooks
+./build/install-build-deps.sh --no-prompt || true
+# Install Chromium's bundled arm64 sysroot (Debian bullseye, glibc 2.31) and build
+# against it (use_sysroot=true below) so the binary links to old glibc/libgcc and
+# runs on Debian 11/12/13+ — not just this host's glibc. runhooks skips it when the
+# host arch != target, so install it explicitly.
+python3 build/linux/sysroot_scripts/install-sysroot.py --arch=arm64
+# Native arm64 gperf at the path blink's scripts.gni expects.
+mkdir -p third_party/gperf/cipd/bin
+cp -f "$(command -v gperf)" third_party/gperf/cipd/bin/gperf
+
+# 3. Swap the x64 node for the pinned arm64 node (DEPS ships linux-x64 only).
+NODE_VER="$(grep -oE 'NODE_VERSION="v[0-9.]+"' third_party/node/update_node_binaries | head -1 | grep -oE 'v[0-9.]+')"
+echo "[$(ts)] node $NODE_VER (arm64 swap)"
+curl -fsSL -o "$TMPDIR/node.tar.xz" "https://nodejs.org/dist/${NODE_VER}/node-${NODE_VER}-linux-arm64.tar.xz"
+tar -C "$TMPDIR" -xf "$TMPDIR/node.tar.xz"
+cp -f "$TMPDIR/node-${NODE_VER}-linux-arm64/bin/node" third_party/node/linux/node-linux-x64/bin/node
+
+# 4. Build clang from source (no aarch64-linux prebuilt exists).
+LLVM="third_party/llvm-build/Release+Asserts"
+if [ ! -x "$LLVM/bin/clang" ] || [ "$(file -b "$LLVM/bin/clang" | grep -c aarch64)" = 0 ]; then
+  echo "[$(ts)] building clang from source (this takes a while)"
+  # build.py fetches an x86-64 cmake; replace with a native arm64 cmake at the same path.
+  python3 tools/clang/scripts/build.py --without-android --without-fuchsia \
+      --host-cc=/usr/bin/gcc --host-cxx=/usr/bin/g++ --disable-asserts \
+      --with-ml-inliner-model='' 2>/dev/null || true   # first pass fetches sources, then fails on x86 cmake
+  CMV=3.26.4
+  if [ -e "third_party/llvm/../llvm-build-tools/cmake-${CMV}-linux-x86_64/bin/cmake" ] && \
+     file -b "third_party/llvm/../llvm-build-tools/cmake-${CMV}-linux-x86_64/bin/cmake" | grep -q x86-64; then
+    D="third_party/llvm/../llvm-build-tools"; rm -rf "$D/cmake-${CMV}-linux-x86_64"
+    curl -fsSL -o "$TMPDIR/cmake.tgz" "https://github.com/Kitware/CMake/releases/download/v${CMV}/cmake-${CMV}-linux-aarch64.tar.gz"
+    tar -C "$D" -xf "$TMPDIR/cmake.tgz"; mv "$D/cmake-${CMV}-linux-aarch64" "$D/cmake-${CMV}-linux-x86_64"
+  fi
+  # --with-ml-inliner-model='' : no arm64 TensorFlow wheel (compiler-internal opt; no effect on output).
+  python3 tools/clang/scripts/build.py --without-android --without-fuchsia \
+      --host-cc=/usr/bin/gcc --host-cxx=/usr/bin/g++ --disable-asserts \
+      --with-ml-inliner-model='' --skip-checkout
+fi
+
+# 5. Rust: no aarch64-linux prebuilt either. Use a rustup nightly matching Chromium's rust date.
+if ! command -v rustup >/dev/null 2>&1; then
+  curl -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain none --profile minimal
+  export PATH="$HOME/.cargo/bin:$PATH"
+fi
+rustup toolchain install "nightly-${RUST_DATE}" --profile minimal -c rust-src -c rustfmt \
+  --target aarch64-unknown-linux-gnu
+BINDGEN_VER="$(grep -oE 'corresponds to [0-9.]+' tools/rust/build_bindgen.py | grep -oE '[0-9.]+' || echo 0.72.1)"
+[ -x "$LLVM/bin/bindgen" ] || cargo install "bindgen-cli@${BINDGEN_VER}" --locked --root "$WORK/bindgen"
+cp -f "$WORK/bindgen/bin/bindgen" "$LLVM/bin/bindgen" 2>/dev/null || true
+# bindgen needs a shared libclang (build.py makes only libclang.a) + rustfmt, at rust_bindgen_root.
+ln -sf "$(ls /usr/lib/llvm-*/lib/libclang.so | head -1)" "$LLVM/lib/libclang.so"
+ln -sf "$RUST_TC/bin/rustfmt" "$LLVM/bin/rustfmt"
+
+# 6. Apply the Fortress stealth patch series (architecture-neutral, unchanged).
+"$REPO/build/apply-patches.sh" "$WORK/chromium/src"
+
+# 6b. bindgen here uses the system libclang (older than the in-tree clang), which
+# rejects a few newer clang-only cflags. They are diagnostic/sanitizer/codegen flags
+# irrelevant to bindgen's type extraction; drop them in Chromium's clang-arg filter.
+FCA="third_party/../build/rust/gni_impl/filter_clang_args.py"
+grep -q "fno-lifetime-dse" "$FCA" || python3 - "$FCA" <<'PY'
+import sys
+p=sys.argv[1]; s=open(p).read()
+a="      elif args[i] == '-ftime-trace':\n        pass\n"
+add=("      elif args[i] in ('-fdiagnostics-show-inlining-chain', '-fno-lifetime-dse'):\n        pass\n"
+     "      elif (args[i].startswith('--warning-suppression-mappings') or\n"
+     "            args[i].startswith('-fsanitize-ignore-for-ubsan-feature')):\n        pass\n")
+open(p,"w").write(s.replace(a,a+add,1))
+PY
+
+# 7. Configure (stealth args + arm64 toolchain args) and build.
+# rustc_version must be space-free (custom toolchain uses it verbatim as rustc_revision).
+RUSTC_VER="$("$RUST_TC/bin/rustc" -V | sed 's/rustc //; s/[() ]/-/g; s/-\{2,\}/-/g; s/-$//')"
+gn gen "out/$OUT" --args="$(cat "$REPO/build/args.arm64.gn")
+clang_base_path = \"//third_party/llvm-build/Release+Asserts\"
+clang_use_chrome_plugins = false
+rust_sysroot_absolute = \"$RUST_TC\"
+rustc_version = \"$RUSTC_VER\"
+rust_bindgen_root = \"//third_party/llvm-build/Release+Asserts\"
+rust_force_head_revision = true
+toolchain_supports_rust_thin_lto = false
+use_sysroot = true
+use_siso = false
+treat_warnings_as_errors = false"
+autoninja -C "out/$OUT" chrome chrome_crashpad_handler
+
+echo "==> Done: $WORK/chromium/src/out/$OUT/chrome"
+"$WORK/chromium/src/out/$OUT/chrome" --version || true
diff --git a/build/build.sh b/build/build.sh
index 8e2ec0d..544c8bf 100755
--- a/build/build.sh
+++ b/build/build.sh
@@ -10,7 +10,13 @@
 set -euo pipefail
 REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 WORK="${1:-$REPO/.fortress-build}"
-ARGS_FILE="$REPO/build/args.gn"
+# Select GN args by host architecture. args.arm64.gn is identical to args.gn
+# except for the architecture-bound bits (target_cpu + no x86 baseline cflags);
+# all stealth patches are architecture-neutral. Override with ARGS_FILE=... .
+case "$(uname -m)" in
+  aarch64|arm64) ARGS_FILE="${ARGS_FILE:-$REPO/build/args.arm64.gn}" ;;
+  *)             ARGS_FILE="${ARGS_FILE:-$REPO/build/args.gn}" ;;
+esac
 OUT="Fortress"
 VER="${CHROMIUM_VERSION:-$(cat "$REPO/CHROMIUM_VERSION")}"
 export TMPDIR="${TMPDIR:-$WORK/tmp}"