diff --git a/configs/airootfs/root/configurator b/configs/airootfs/root/configurator
index 4cd3db3d..c79331c2 100644
--- a/configs/airootfs/root/configurator
+++ b/configs/airootfs/root/configurator
@@ -435,6 +435,21 @@ disk_abort_hook() {
   abort "$1"
 }
 
+# Argon2id --pbkdf-memory (KiB) for live-ISO luksFormat.
+# Requires omarchy-luks-pbkdf-memory to exit 0 with a numeric value; do not
+# probe with `command -v` (bash reports non-executables as found).
+luks_pbkdf_memory_kib() {
+  local out
+  if ! out=$(omarchy-luks-pbkdf-memory); then
+    return 1
+  fi
+  if ! [[ $out =~ ^[0-9]+$ ]]; then
+    echo "omarchy-luks-pbkdf-memory produced non-numeric output: ${out}" >&2
+    return 1
+  fi
+  printf '%s\n' "$out"
+}
+
 # Save the configurator answers the installer consumes: git identity and
 # encryption choice as plain files, account details as archinstall credentials.
 # Deferred-provisioning installs defer the user to first boot: no credentials, and on encrypted
@@ -730,11 +745,18 @@ run_partition_execute() {
 
     if [[ "$encrypt_installation" == "true" ]]; then
       step "Setting up LUKS2 on $root_partition_device"
+      local pbkdf_memory
+      if ! pbkdf_memory=$(luks_pbkdf_memory_kib); then
+        disk_abort_hook "Could not choose a safe LUKS Argon2id memory cost"
+      fi
+      say --foreground 8 "LUKS Argon2id memory cost: ${pbkdf_memory} KiB"
       # Kept as pipes rather than routed through disk_step: the passphrase must
       # not become an argv the process table can show. Folding stderr into
       # stdout still lands any error in the install log.
       if ! printf "%s" "$password" |
-        cryptsetup luksFormat --type luks2 --batch-mode "$root_partition_device" - 2>&1; then
+        cryptsetup luksFormat --type luks2 --batch-mode \
+          --pbkdf argon2id --pbkdf-memory "$pbkdf_memory" --iter-time 2000 \
+          "$root_partition_device" - 2>&1; then
         disk_abort_hook "Formatting LUKS2 on $root_partition_device failed"
       fi
       if ! printf "%s" "$password" |
diff --git a/configs/airootfs/usr/local/bin/omarchy-iso-install b/configs/airootfs/usr/local/bin/omarchy-iso-install
index 59aca95b..3f21e32a 100755
--- a/configs/airootfs/usr/local/bin/omarchy-iso-install
+++ b/configs/airootfs/usr/local/bin/omarchy-iso-install
@@ -23,5 +23,134 @@ while [[ $# -gt 0 ]]; do
   esac
 done
 
+# Patch archinstall's Luks2.encrypt before Python imports it.
+#
+# Full-disk encrypted installs still go through archinstall's cryptsetup
+# luksFormat. Without --pbkdf-memory, argon2id defaults to ~1 GiB and the
+# kernel OOM-kills cryptsetup on constrained live/PXE boots (SIGKILL: 9).
+# Locate luks.py via sys.path (do not importlib.util.find_spec: that imports
+# archinstall as a side effect). Fail closed on the encrypted path: a missed
+# patch would reintroduce the SIGKILL.
+# Ask disk_config.disk_encryption, the same field archinstall_adapter.is_encrypted
+# reads to decide whether luksFormat runs at all. The flag file is only a
+# fallback: README calls it the autologin signal, not the encryption one.
+install_is_encrypted() {
+  local encryption_type=no_encryption encrypt=true
+
+  if [[ -n ${OMARCHY_INSTALL_CONFIG:-} && -r $OMARCHY_INSTALL_CONFIG ]]; then
+    encryption_type=$(jq -r '
+      .disk_config.disk_encryption
+      | if . == null then "no_encryption" else (.encryption_type // "luks") end
+    ' "$OMARCHY_INSTALL_CONFIG" 2>/dev/null) || encryption_type=luks
+  fi
+  if [[ $encryption_type != no_encryption ]]; then
+    return 0
+  fi
+
+  if [[ -n ${OMARCHY_INSTALL_ENCRYPT_FILE:-} && -r $OMARCHY_INSTALL_ENCRYPT_FILE ]]; then
+    encrypt=$(tr -d '[:space:]' <"$OMARCHY_INSTALL_ENCRYPT_FILE")
+  fi
+  # The same values context.py accepts for the same file.
+  [[ ${encrypt,,} == true || ${encrypt,,} == yes || ${encrypt,,} == 1 ]]
+}
+
+read_pbkdf_memory() {
+  local out
+  if ! out=$(omarchy-luks-pbkdf-memory); then
+    echo "omarchy-iso-install: omarchy-luks-pbkdf-memory failed" >&2
+    return 1
+  fi
+  if ! [[ $out =~ ^[0-9]+$ ]]; then
+    echo "omarchy-iso-install: omarchy-luks-pbkdf-memory produced non-numeric output: ${out}" >&2
+    return 1
+  fi
+  printf '%s\n' "$out"
+}
+
+patch_archinstall_luks_pbkdf_memory() {
+  local luks_py pbkdf_memory
+
+  if ! install_is_encrypted; then
+    return 0
+  fi
+
+  # 4.x moved Luks2 to lib/disk/luks.py; 3.x kept it at lib/luks.py. Prefer
+  # 4.x (what the ISO ships) then 3.x so a locator miss does not abort an
+  # encrypted install on an older tree. Fail closed either way.
+  luks_py=$(python - <<'PY'
+import sys
+from pathlib import Path
+
+relatives = (
+    Path("archinstall") / "lib" / "disk" / "luks.py",  # 4.x
+    Path("archinstall") / "lib" / "luks.py",           # 3.x
+)
+for entry in sys.path:
+    for rel in relatives:
+        candidate = Path(entry) / rel
+        if candidate.is_file():
+            print(candidate)
+            sys.exit(0)
+sys.exit(1)
+PY
+  ) || {
+    echo "omarchy-iso-install: could not locate archinstall luks.py on sys.path (tried lib/disk/luks.py and lib/luks.py)" >&2
+    exit 1
+  }
+
+  if [[ ! -f $luks_py ]]; then
+    echo "omarchy-iso-install: archinstall luks.py is not a file: ${luks_py}" >&2
+    exit 1
+  fi
+  if [[ ! -w $luks_py ]]; then
+    echo "omarchy-iso-install: archinstall luks.py is not writable: ${luks_py}" >&2
+    exit 1
+  fi
+
+  pbkdf_memory=$(read_pbkdf_memory) || exit 1
+
+  echo "omarchy-iso-install: capping archinstall LUKS Argon2id memory to ${pbkdf_memory} KiB" >&2
+
+  # Insert --pbkdf-memory after the --iter-time value in the cmd list.
+  # Same encrypt argv in 3.x (lib/luks.py) and 4.x (lib/disk/luks.py):
+  #   '--iter-time', str(iter_time), *key_file_arg, '--use-urandom',
+  python - "$luks_py" "$pbkdf_memory" <<'PY'
+from pathlib import Path
+import re
+import sys
+
+path = Path(sys.argv[1])
+memory = sys.argv[2]
+text = path.read_text()
+
+# Already patched: refresh the value rather than keep the first run's. A retry
+# in the same live session re-reads MemAvailable and can land on the other side
+# of the floor, and the log would name a cost archinstall never used.
+already = re.compile(
+    r"(['\"]--iter-time['\"],\s*str\(iter_time\),\s*['\"]--pbkdf-memory['\"],\s*)['\"][^'\"]*['\"]",
+)
+refreshed, n = already.subn(rf"\g<1>'{memory}'", text, count=1)
+if n == 1:
+    path.write_text(refreshed)
+    sys.exit(0)
+
+pattern = re.compile(
+    r"(['\"]--iter-time['\"],\s*str\(iter_time\),)",
+    re.MULTILINE,
+)
+replacement = rf"\1\n\t\t\t'--pbkdf-memory',\n\t\t\t'{memory}',"
+new_text, n = pattern.subn(replacement, text, count=1)
+if n != 1:
+    sys.stderr.write(
+        f"omarchy-iso-install: could not patch {path} for --pbkdf-memory "
+        f"(matches={n})\n"
+    )
+    sys.exit(1)
+path.write_text(new_text)
+PY
+}
+
+patch_archinstall_luks_pbkdf_memory
+
 cd /usr/share/omarchy-iso
 exec python -m orchestrator.main
diff --git a/configs/airootfs/usr/local/bin/omarchy-luks-pbkdf-memory b/configs/airootfs/usr/local/bin/omarchy-luks-pbkdf-memory
new file mode 100755
index 00000000..8fa1307e
--- /dev/null
+++ b/configs/airootfs/usr/local/bin/omarchy-luks-pbkdf-memory
@@ -0,0 +1,52 @@
+#!/bin/bash
+# Print Omarchy's Argon2id --pbkdf-memory (KiB) for live-ISO LUKS formatting.
+#
+# cryptsetup's argon2id default (~1 GiB) is OOM-killed on constrained live/PXE
+# boots (cryptsetup dies with SIGKILL 9). Omarchy uses a fixed 256 MiB default
+# so every install gets the same KDF parameters. We only step down to the
+# RFC 9106 64 MiB floor when that default cannot fit, and we refuse to format
+# if even the floor cannot.
+#
+# Argon2id attacker cost scales with memory squared times passes. Lowering
+# --pbkdf-memory is a real hardness reduction; --iter-time does not make up
+# for it. That is why the default is a fixed Omarchy value rather than a
+# function of whatever MemAvailable happens to be at format time.
+#
+# OMARCHY_LUKS_MEMINFO may point at an alternate meminfo file (used by tests).
+
+set -euo pipefail
+
+default_kib=262144 # 256 MiB — Omarchy Argon2id memory cost
+floor_kib=65536    # 64 MiB — RFC 9106 memory-constrained recommendation
+
+# cryptsetup will try to lock --pbkdf-memory KiB. Leave at least as much
+# again for the rest of the live session so the allocation cannot consume
+# all of MemAvailable.
+fits() {
+  local need=$1 avail=$2
+  ((avail >= need * 2))
+}
+
+meminfo=${OMARCHY_LUKS_MEMINFO:-/proc/meminfo}
+avail_kib=0
+if [[ -r $meminfo ]]; then
+  avail_kib=$(awk '/^MemAvailable:/ { print $2; exit }' "$meminfo" 2>/dev/null || echo 0)
+fi
+
+if ! [[ $avail_kib =~ ^[0-9]+$ ]]; then
+  avail_kib=0
+fi
+
+if fits "$default_kib" "$avail_kib"; then
+  printf '%s\n' "$default_kib"
+  exit 0
+fi
+
+if fits "$floor_kib" "$avail_kib"; then
+  echo "omarchy-luks-pbkdf-memory: MemAvailable ${avail_kib} KiB cannot fit the ${default_kib} KiB Omarchy default; using ${floor_kib} KiB floor" >&2
+  printf '%s\n' "$floor_kib"
+  exit 0
+fi
+
+echo "omarchy-luks-pbkdf-memory: MemAvailable ${avail_kib} KiB is too small to fit even the ${floor_kib} KiB Argon2id floor; refusing LUKS format" >&2
+exit 1
diff --git a/configs/profiledef.sh b/configs/profiledef.sh
index 268a3cea..9bdc0d31 100644
--- a/configs/profiledef.sh
+++ b/configs/profiledef.sh
@@ -40,6 +40,7 @@ file_permissions=(
   ["/usr/local/bin/omarchy-iso-cleanup-disk"]="0:0:755"
   ["/usr/local/bin/omarchy-install-dashboard"]="0:0:755"
   ["/usr/local/bin/omarchy-iso-install"]="0:0:755"
+  ["/usr/local/bin/omarchy-luks-pbkdf-memory"]="0:0:755"
   ["/usr/local/bin/omarchy-upload-log"]="0:0:755"
   ["/var/cache/omarchy/mirror/offline/"]="0:0:775"
 )
diff --git a/test/unit/luks-pbkdf-memory-test.sh b/test/unit/luks-pbkdf-memory-test.sh
new file mode 100755
index 00000000..43f9b8ba
--- /dev/null
+++ b/test/unit/luks-pbkdf-memory-test.sh
@@ -0,0 +1,72 @@
+#!/bin/bash
+#
+# Drive omarchy-luks-pbkdf-memory against fake meminfo files. The helper must
+# be invoked for every assertion; inlining the formula would let a stubbed
+# helper (printf '65536\n') pass.
+
+set -euo pipefail
+
+ROOT=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/../.." && pwd)
+helper="$ROOT/configs/airootfs/usr/local/bin/omarchy-luks-pbkdf-memory"
+
+pass() {
+  printf 'ok - %s\n' "$1"
+}
+
+fail() {
+  local description="$1"
+  local detail="${2:-}"
+  printf 'not ok - %s\n' "$description" >&2
+  [[ -n $detail ]] && printf '%s\n' "$detail" >&2
+  exit 1
+}
+
+[[ -x $helper ]] || fail "helper is executable" "missing $helper"
+
+fake_meminfo=$(mktemp)
+trap 'rm -f "$fake_meminfo"' EXIT
+
+run_helper() {
+  OMARCHY_LUKS_MEMINFO="$fake_meminfo" "$helper"
+}
+
+# 4 GiB available: 2x the 256 MiB default fits.
+printf 'MemAvailable:    4194304 kB\n' >"$fake_meminfo"
+out=$(run_helper) || fail "default on plenty of RAM" "helper exited $?"
+[[ $out == 262144 ]] || fail "default on plenty of RAM" "expected 262144, got $out"
+pass "default 256 MiB when MemAvailable is 4 GiB"
+
+# 512 MiB available: 256 MiB default needs 512 MiB free (2x), so this is the
+# exact threshold for the default.
+printf 'MemAvailable:    524288 kB\n' >"$fake_meminfo"
+out=$(run_helper) || fail "default at 2x threshold" "helper exited $?"
+[[ $out == 262144 ]] || fail "default at 2x threshold" "expected 262144, got $out"
+pass "default 256 MiB when MemAvailable is exactly 2x 256 MiB"
+
+# Just under 2x default (511 MiB): cannot fit 256 MiB, can fit 64 MiB floor.
+printf 'MemAvailable:    523264 kB\n' >"$fake_meminfo"
+out=$(run_helper 2>/dev/null) || fail "floor when default cannot fit" "helper exited $?"
+[[ $out == 65536 ]] || fail "floor when default cannot fit" "expected 65536, got $out"
+pass "64 MiB floor when MemAvailable cannot fit 256 MiB"
+
+# 128 MiB available: exact 2x floor threshold.
+printf 'MemAvailable:    131072 kB\n' >"$fake_meminfo"
+out=$(run_helper 2>/dev/null) || fail "floor at 2x threshold" "helper exited $?"
+[[ $out == 65536 ]] || fail "floor at 2x threshold" "expected 65536, got $out"
+pass "64 MiB floor when MemAvailable is exactly 2x 64 MiB"
+
+# 64 MiB available: floor itself cannot fit (would consume all free RAM).
+printf 'MemAvailable:    65536 kB\n' >"$fake_meminfo"
+if out=$(run_helper 2>/dev/null); then
+  fail "refuse when floor cannot fit" "helper printed $out instead of failing"
+fi
+pass "refuses to format when MemAvailable cannot fit the 64 MiB floor"
+
+# Unreadable / missing MemAvailable: treat as 0 and refuse.
+printf 'MemTotal:    16777216 kB\n' >"$fake_meminfo"
+if out=$(run_helper 2>/dev/null); then
+  fail "refuse without MemAvailable" "helper printed $out instead of failing"
+fi
+pass "refuses to format when meminfo has no MemAvailable"
+
+echo "luks-pbkdf-memory-test: ok"