diff --git a/install.sh b/install.sh
index 1ce30a3..e6bc86e 100755
--- a/install.sh
+++ b/install.sh
@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 # NVIDIA installer: beside the proxy release's d4r/ or inside the ASI's d4r/.
-# Installs NVIDIA's DLLs and then builds the native engine's models from them on this machine.
+# Installs NVIDIA's DLLs and then builds the native engine's models from them on this machine. Both are kept in
+# ~/.cache/d4r, so the next game's install copies them instead of downloading or building again.
 set -euo pipefail
 DLSS_URL=https://raw.githubusercontent.com/NVIDIA/DLSS/a291cc7d2cc642a51566f3dfd5376f635cd1b284/lib/Windows_x86_64/rel/nvngx_dlss.dll
 DLSS_SHA256=be6e434a94ca32499515eb62ca0e6c274526055d568d0426e4c652dcdfb6ee6e
@@ -12,23 +13,29 @@ NGX_SHA256=0e3423b3b7afa1019c7ecac053a8408df8e5d9d9d904434705c6aaeacec02fef
 
 fail() { printf 'install.sh: %s\n' "$*" >&2; exit 1; }
 usage() {
-  printf '%s\n' 'Usage: bash install.sh [--no-engine | --engine-only] [--rebuild-engine] [extracted-release-directory]' \
-    'Default: the directory containing this script, regardless of your working directory.' \
+  printf '%s\n' 'Usage: bash install.sh [options] [extracted-release-directory]' \
+    'Default directory: the one containing this script, regardless of your working directory.' \
+    'Run it from a terminal and it asks what to do. The options answer those questions in advance:' \
+    '  --yes             accept every default (also the behaviour without a terminal)' \
+    '  --no-engine       only the NVIDIA DLLs, no engine models' \
+    '  --engine-only     only the engine models (the DLLs are already installed)' \
+    '  --exact           engine models with NVIDIA'"'"'s exact roundings (slower) instead of the fastest builds' \
+    '  --rebuild-engine  build the models again even when a cached build fits' \
     '1. Downloads official NVIDIA DLSS 310.7.0 (Super Resolution), DLSS Ray Reconstruction 310.9.1 and NGX from' \
-    '   driver 596.36 (~1 GiB in all). Existing matching DLLs are kept; differing DLLs are backed up.' \
-    '2. Builds the native engine'"'"'s models ([Engine] in d4r/d4r.ini) from those DLLs into d4r/engine:' \
-    '   Ray Reconstruction D, E and F from nvngx_dlssd.dll; Super Resolution K, M and L (and their LDR variants)' \
-    '   by rendering one test frame per model through d4r under GE-Proton (about a minute each).' \
-    '   --no-engine skips this, --engine-only does only this, --rebuild-engine rebuilds models already built.' \
+    '   driver 596.36 (~1 GiB, once: verified copies are kept in ~/.cache/d4r/nvidia).' \
+    '2. Builds the native engine'"'"'s models from those DLLs into d4r/engine (once per DLL set and builder version:' \
+    '   ~/.cache/d4r/engine-models). The engine is the faster path; d4r.ini [Engine] Enabled = auto uses it.' \
     'Requires Bash, curl, sha256sum, 7zz/7z/7za, python3 with numpy, and GE-Proton 11 in Steam (or' \
-    'D4R_PROTON=/path/to/GE-Proton11-3). No sudo needed. NVIDIA license terms apply.'
+    'D4R_PROTON=/path/to/GE-Proton11-3). No sudo needed. NVIDIA license terms apply. D4R_CACHE_DIR moves the cache.'
 }
-DO_DLLS=1 DO_ENGINE=1 REBUILD=0
+DO_DLLS=1 DO_ENGINE=ask EXACT=ask REBUILD=0 YES=0
 while [[ $# -gt 0 ]]; do
   case "$1" in
     -h|--help) usage; exit 0 ;;
+    -y|--yes) YES=1; shift ;;
     --no-engine) DO_ENGINE=0; shift ;;
-    --engine-only) DO_DLLS=0; shift ;;
+    --engine-only) DO_DLLS=0; DO_ENGINE=1; shift ;;
+    --exact) EXACT=1; shift ;;
     --rebuild-engine) REBUILD=1; shift ;;
     -*) usage >&2; exit 2 ;;
     *) break ;;
@@ -41,49 +48,21 @@ RUNTIME="$ROOT/d4r"
 [[ -f "$RUNTIME/nvngx.dll" && -f "$RUNTIME/d4r.ini" ]] || fail "Extract the release ZIP first; no d4r runtime found in $ROOT"
 command -v sha256sum >/dev/null || fail 'Missing sha256sum (install coreutils).'
 valid() { [[ -f "$1" ]] && [[ $(sha256sum -- "$1" | cut -d' ' -f1) == "$2" ]]; }
+CACHE="${D4R_CACHE_DIR:-${XDG_CACHE_HOME:-$HOME/.cache}/d4r}"
 
-install_dlls() {
-  local need_dlss=1 need_dlssd=1 need_ngx=1 tool
-  valid "$RUNTIME/nvngx_dlss.dll" "$DLSS_SHA256" && need_dlss=0
-  valid "$RUNTIME/nvngx_dlssd.dll" "$DLSSD_SHA256" && need_dlssd=0
-  valid "$RUNTIME/ngx/_nvngx.dll" "$NGX_SHA256" && need_ngx=0
-  if (( need_dlss == 0 && need_dlssd == 0 && need_ngx == 0 )); then
-    echo 'NVIDIA DLLs are already installed and verified.'
-    return
-  fi
-  command -v curl >/dev/null || fail 'Missing curl. Install it and run this script again.'
-  SEVENZIP=''
-  if (( need_ngx )); then
-    for tool in 7zz 7z 7za; do
-      if command -v "$tool" >/dev/null; then SEVENZIP=$tool; break; fi
-    done
-    [[ -n "$SEVENZIP" ]] || fail 'Missing 7-Zip. Install 7zip (or p7zip) and run this script again.'
-  fi
-  echo 'Downloading NVIDIA files under NVIDIA license terms:'
-  echo 'DLSS: https://github.com/NVIDIA/DLSS/blob/v310.9.1/LICENSE.txt'
-  echo 'Driver: https://www.nvidia.com/en-us/drivers/nvidia-license/'
-  if (( need_dlss )); then
-    echo 'Downloading DLSS 310.7.0...'
-    download "$DLSS_URL" "$TMP/nvngx_dlss.dll"
-    verify "$TMP/nvngx_dlss.dll" "$DLSS_SHA256"
-  fi
-  if (( need_dlssd )); then
-    echo 'Downloading DLSS Ray Reconstruction 310.9.1...'
-    download "$DLSSD_URL" "$TMP/nvngx_dlssd.dll"
-    verify "$TMP/nvngx_dlssd.dll" "$DLSSD_SHA256"
-  fi
-  if (( need_ngx )); then
-    echo 'Downloading NVIDIA driver 596.36 (~915 MiB); extracting NGX without running the installer...'
-    download "$DRIVER_URL" "$TMP/driver.exe"
-    verify "$TMP/driver.exe" "$DRIVER_SHA256"
-    "$SEVENZIP" e -y -bso0 -bsp0 "-o$TMP/ngx" "$TMP/driver.exe" 'Display.Driver/_nvngx.dll' || fail 'Could not extract NGX; no DLLs installed.'
-    verify "$TMP/ngx/_nvngx.dll" "$NGX_SHA256"
-  fi
-  # Verify all downloads before modifying any destination.
-  (( need_dlss == 0 )) || place "$TMP/nvngx_dlss.dll" "$RUNTIME/nvngx_dlss.dll"
-  (( need_dlssd == 0 )) || place "$TMP/nvngx_dlssd.dll" "$RUNTIME/nvngx_dlssd.dll"
-  (( need_ngx == 0 )) || place "$TMP/ngx/_nvngx.dll" "$RUNTIME/ngx/_nvngx.dll"
-  echo 'NVIDIA DLLs installed and verified.'
+# Questions only on a terminal; otherwise (or with --yes) every default applies.
+interactive() { (( YES == 0 )) && [[ -t 0 && -t 1 ]]; }
+ask() {   # ask "QUESTION" DEFAULT(y|n): 0 for yes
+  local answer
+  if ! interactive; then [[ $2 == y ]]; return; fi
+  while true; do
+    read -r -p "$1 [$([[ $2 == y ]] && echo Y/n || echo y/N)] " answer || answer=''
+    case "${answer,,}" in
+      '') [[ $2 == y ]]; return ;;
+      y|yes) return 0 ;;
+      n|no) return 1 ;;
+    esac
+  done
 }
 
 TMP=$(mktemp -d)
@@ -92,7 +71,7 @@ trap '[[ -z "$STAGED" ]] || rm -f -- "$STAGED"; rm -rf -- "$TMP"' EXIT
 trap 'exit 130' INT
 trap 'exit 143' TERM
 download() {
-  curl --fail --location --show-error --retry 3 --connect-timeout 30 \
+  curl --fail --location --show-error --retry 3 --connect-timeout 30 --progress-bar \
     --proto '=https' --proto-redir '=https' --output "$2" "$1" || fail "Download failed: $1. Run the installer again to retry."
 }
 verify() { valid "$1" "$2" || fail "SHA-256 mismatch for $1; no DLLs installed."; }
@@ -113,37 +92,154 @@ place() {
   STAGED=''
   printf 'Installed: %s\n' "$dst"
 }
+# A verified copy in the cache, or none. Cached files are checked again before use.
+cached() { local f="$CACHE/nvidia/$1"; valid "$f" "$2" && printf '%s\n' "$f"; }
+keep() { mkdir -p -- "$CACHE/nvidia" && cp -- "$1" "$CACHE/nvidia/$2.tmp" && mv -f -- "$CACHE/nvidia/$2.tmp" "$CACHE/nvidia/$2"; }
+
+install_dlls() {
+  local need_dlss=1 need_dlssd=1 need_ngx=1 tool src
+  valid "$RUNTIME/nvngx_dlss.dll" "$DLSS_SHA256" && need_dlss=0
+  valid "$RUNTIME/nvngx_dlssd.dll" "$DLSSD_SHA256" && need_dlssd=0
+  valid "$RUNTIME/ngx/_nvngx.dll" "$NGX_SHA256" && need_ngx=0
+  if (( need_dlss == 0 && need_dlssd == 0 && need_ngx == 0 )); then
+    echo 'NVIDIA DLLs are already installed and verified.'
+    return
+  fi
+  # earlier installs' verified copies first
+  if (( need_dlss )) && src=$(cached nvngx_dlss.dll "$DLSS_SHA256"); then cp -- "$src" "$TMP/nvngx_dlss.dll"; need_dlss=2; fi
+  if (( need_dlssd )) && src=$(cached nvngx_dlssd.dll "$DLSSD_SHA256"); then cp -- "$src" "$TMP/nvngx_dlssd.dll"; need_dlssd=2; fi
+  if (( need_ngx )) && src=$(cached _nvngx.dll "$NGX_SHA256"); then mkdir -p "$TMP/ngx"; cp -- "$src" "$TMP/ngx/_nvngx.dll"; need_ngx=2; fi
+  if (( need_dlss == 1 || need_dlssd == 1 || need_ngx == 1 )); then
+    local size=0
+    (( need_dlss != 1 )) || size=$((size + 57))
+    (( need_dlssd != 1 )) || size=$((size + 47))
+    (( need_ngx != 1 )) || size=$((size + 915))
+    echo "d4r needs NVIDIA's DLSS files, downloaded from NVIDIA under NVIDIA's license terms:"
+    echo '  DLSS: https://github.com/NVIDIA/DLSS/blob/v310.9.1/LICENSE.txt'
+    echo '  Driver: https://www.nvidia.com/en-us/drivers/nvidia-license/'
+    ask "Download them now (~$size MiB, once: later installs use $CACHE/nvidia)?" y ||
+      fail 'Not downloaded. d4r needs these files; run install.sh again when you want to install them.'
+    command -v curl >/dev/null || fail 'Missing curl. Install it and run this script again.'
+    SEVENZIP=''
+    if (( need_ngx == 1 )); then
+      for tool in 7zz 7z 7za; do
+        if command -v "$tool" >/dev/null; then SEVENZIP=$tool; break; fi
+      done
+      [[ -n "$SEVENZIP" ]] || fail 'Missing 7-Zip. Install 7zip (or p7zip) and run this script again.'
+    fi
+  fi
+  if (( need_dlss == 1 )); then
+    echo 'Downloading DLSS 310.7.0...'
+    download "$DLSS_URL" "$TMP/nvngx_dlss.dll"
+    verify "$TMP/nvngx_dlss.dll" "$DLSS_SHA256"
+    keep "$TMP/nvngx_dlss.dll" nvngx_dlss.dll
+  fi
+  if (( need_dlssd == 1 )); then
+    echo 'Downloading DLSS Ray Reconstruction 310.9.1...'
+    download "$DLSSD_URL" "$TMP/nvngx_dlssd.dll"
+    verify "$TMP/nvngx_dlssd.dll" "$DLSSD_SHA256"
+    keep "$TMP/nvngx_dlssd.dll" nvngx_dlssd.dll
+  fi
+  if (( need_ngx == 1 )); then
+    echo 'Downloading NVIDIA driver 596.36 (~915 MiB); extracting NGX without running the installer...'
+    download "$DRIVER_URL" "$TMP/driver.exe"
+    verify "$TMP/driver.exe" "$DRIVER_SHA256"
+    "$SEVENZIP" e -y -bso0 -bsp0 "-o$TMP/ngx" "$TMP/driver.exe" 'Display.Driver/_nvngx.dll' || fail 'Could not extract NGX; no DLLs installed.'
+    rm -f -- "$TMP/driver.exe"
+    verify "$TMP/ngx/_nvngx.dll" "$NGX_SHA256"
+    keep "$TMP/ngx/_nvngx.dll" _nvngx.dll
+  fi
+  # Everything is verified before any destination changes.
+  (( need_dlss == 0 )) || place "$TMP/nvngx_dlss.dll" "$RUNTIME/nvngx_dlss.dll"
+  (( need_dlssd == 0 )) || place "$TMP/nvngx_dlssd.dll" "$RUNTIME/nvngx_dlssd.dll"
+  (( need_ngx == 0 )) || place "$TMP/ngx/_nvngx.dll" "$RUNTIME/ngx/_nvngx.dll"
+  echo 'NVIDIA DLLs installed and verified.'
+}
 
 (( DO_DLLS == 0 )) || install_dlls
-if (( DO_ENGINE == 0 )); then
-  echo 'Follow the included README for Steam launch options.'
-  exit 0
-fi
 
-# The engine's models, built from the DLLs above. A stamp of the DLLs and the builder skips an unchanged rebuild.
+# --- the engine's models ---------------------------------------------------------------------------------------
 BUILDER="$RUNTIME/tools/build-engine-models.sh"
-[[ -f "$BUILDER" ]] || fail "missing $BUILDER (this release has no engine-model builder; use --no-engine)"
-STAMP="$RUNTIME/engine/.d4r-models"
-stamp() {
-  { sha256sum -- "$RUNTIME/nvngx_dlss.dll" "$RUNTIME/nvngx_dlssd.dll" 2>/dev/null | cut -d' ' -f1
-    (cd "$RUNTIME/tools" && find . -type f ! -name '*.pyc' -print0 | LC_ALL=C sort -z | xargs -0 sha256sum); } | sha256sum | cut -d' ' -f1
-}
+done_msg() { echo 'Done. Follow the included README for Steam launch options.'; }
+if [[ ! -f "$BUILDER" ]]; then
+  [[ "$DO_ENGINE" != 1 ]] || fail "missing $BUILDER (this release has no engine-model builder)"
+  done_msg; exit 0
+fi
 models=(rr-d rr-e rr-f k k-ldr m m-ldr l l-ldr)
-complete=1
-for m in "${models[@]}"; do [[ -d "$RUNTIME/engine/$m" ]] || complete=0; done
-if (( REBUILD == 0 && complete )) && [[ -f "$STAMP" && "$(cat "$STAMP")" == "$(stamp)" ]]; then
-  echo 'Engine models are already built for these DLLs (--rebuild-engine builds them again).'
-  exit 0
+# One build serves every game with the same DLLs and builder: the key covers both and the accuracy choice.
+key() {   # key EXACT(0|1)
+  { echo "exact=$1"
+    sha256sum -- "$RUNTIME/nvngx_dlss.dll" "$RUNTIME/nvngx_dlssd.dll" 2>/dev/null | cut -d' ' -f1
+    (cd "$RUNTIME/tools" && find . -type f ! -name '*.pyc' -print0 | LC_ALL=C sort -z | xargs -0 sha256sum); } | sha256sum | cut -c1-16
+}
+have() { local m; for m in "${models[@]}"; do [[ -f "$1/$m/model.json" || -f "$1/$m/rr.txt" ]] || return 1; done; }
+STAMP="$RUNTIME/engine/.d4r-models"
+if [[ "$EXACT" == ask ]]; then
+  EXACT=0
+  for e in 0 1; do [[ -f "$STAMP" && "$(cat "$STAMP")" == "$(key $e)" ]] && EXACT=$e; done
 fi
-rm -f -- "$STAMP"
-failed=()
-bash "$BUILDER" --rr-only "$RUNTIME" || failed+=('Ray Reconstruction')
-bash "$BUILDER" --sr-only "$RUNTIME" || failed+=('Super Resolution')
-if (( ${#failed[@]} )); then
-  printf 'install.sh: the engine models for %s were not built (reason above). d4r works without them on its\n' \
-    "$(IFS=/; echo "${failed[*]}")" >&2
-  printf 'normal path; fix the cause and run: bash install.sh --engine-only\n' >&2
-  exit 1
+if (( REBUILD == 0 )) && [[ "$DO_ENGINE" != 0 && -f "$STAMP" && "$(cat "$STAMP")" == "$(key "$EXACT")" ]] && have "$RUNTIME/engine"; then
+  echo 'The engine models in this folder are up to date.'
+  done_msg; exit 0
 fi
-stamp > "$STAMP"
-echo 'Done. Follow the included README for Steam launch options; set [Engine] Enabled = true in d4r/d4r.ini to use the engine.'
+if [[ "$DO_ENGINE" == ask ]]; then
+  echo
+  echo "Set up d4r's own DLSS engine (recommended)?"
+  echo '  + Faster: DLSS 4 / 4.5 and Ray Reconstruction run on d4r'"'"'s Vulkan engine instead of NVIDIA'"'"'s kernels'
+  echo '    through CUDA emulation (for example Ray Reconstruction at 720p -> 4K in about 3.6 ms per frame).'
+  echo '  + Lower latency: the game shows the upscaled result of the frame it just rendered, not an older one.'
+  echo '  + No minute-long freeze while DLSS'"'"'s CUDA kernels compile the first time a model is used.'
+  echo '  - Longer setup, once: building its models takes a minute or two (it renders a test frame per model'
+  echo '    through GE-Proton) and needs ~300 MB of temporary space. Later installs reuse the models.'
+  echo '  Without it, d4r uses its normal path; anything the engine does not cover uses that path anyway.'
+  if ask 'Set up the engine now?' y; then DO_ENGINE=1; else DO_ENGINE=0; fi
+fi
+if [[ "$DO_ENGINE" == 0 ]]; then
+  echo 'No engine models: d4r uses its normal path. Run install.sh again to build them later.'
+  done_msg; exit 0
+fi
+KEY="$(key "$EXACT")"
+SHARED="$CACHE/engine-models/$KEY"
+copy_models() {   # copy_models FROM TO: whole model folders, each replaced by a rename
+  local m
+  mkdir -p -- "$2"
+  for m in "${models[@]}"; do
+    rm -rf -- "$2/$m.new"; cp -r -- "$1/$m" "$2/$m.new"
+    rm -rf -- "$2/$m.old"; [[ ! -e "$2/$m" ]] || mv -- "$2/$m" "$2/$m.old"
+    mv -- "$2/$m.new" "$2/$m"; rm -rf -- "$2/$m.old"
+  done
+}
+if (( REBUILD == 0 )) && have "$SHARED"; then
+  echo "Using the engine models built earlier ($SHARED)."
+  copy_models "$SHARED" "$RUNTIME/engine"
+else
+  failed=()
+  flags=(); (( EXACT == 0 )) || flags=(--exact)
+  bash "$BUILDER" --rr-only "${flags[@]}" "$RUNTIME" || failed+=('Ray Reconstruction')
+  if [[ -z "${D4R_PROTON:-}" && -z "$(bash "$BUILDER" --find-proton)" ]] && interactive; then
+    echo 'The Super Resolution models render one test frame through GE-Proton 11, which was not found in Steam.'
+    read -r -p 'Path to a GE-Proton folder (Enter to skip): ' D4R_PROTON || D4R_PROTON=''
+    export D4R_PROTON
+  fi
+  if [[ -n "${D4R_PROTON:-}" || -n "$(bash "$BUILDER" --find-proton)" ]]; then
+    bash "$BUILDER" --sr-only "${flags[@]}" "$RUNTIME" || failed+=('Super Resolution')
+  else
+    failed+=('Super Resolution')
+    echo 'install.sh: no GE-Proton 11 found for the Super Resolution models.' >&2
+  fi
+  if (( ${#failed[@]} )); then
+    printf 'install.sh: the engine models for %s were not built (reason above). d4r runs those on its normal path;\n' \
+      "$(IFS=/; echo "${failed[*]}")" >&2
+    printf 'fix the cause and run install.sh again.\n' >&2
+    exit 1
+  fi
+  # keep a copy for the next game
+  rm -rf -- "$SHARED.tmp"; mkdir -p -- "$SHARED.tmp"
+  for m in "${models[@]}"; do cp -r -- "$RUNTIME/engine/$m" "$SHARED.tmp/"; done
+  rm -rf -- "$SHARED"; mv -- "$SHARED.tmp" "$SHARED"
+fi
+printf '%s\n' "$KEY" > "$STAMP"
+if grep -qiE '^[[:space:]]*Enabled[[:space:]]*=[[:space:]]*(false|0|no|off)[[:space:]]*$' <(sed -n '/^\[Engine\]/,/^\[/p' "$RUNTIME/d4r.ini"); then
+  echo 'Note: d4r/d4r.ini turns the engine off ([Engine] Enabled = false); set it to auto to use these models.'
+fi
+done_msg
diff --git a/packaging/D4R_README.txt b/packaging/D4R_README.txt
index 9d8002a..075110b 100644
--- a/packaging/D4R_README.txt
+++ b/packaging/D4R_README.txt
@@ -57,13 +57,14 @@ that archive's d4r/README.txt: setup runs automatically when the ASI loads.
 @installer    d4r/ngx/_nvngx.dll. No sudo is needed. The driver archive is about 915 MiB; it is extracted,
 @installer    never executed. Downloads are temporary. Run it again to check the files; differing existing
 @installer    DLLs are backed up before replacement.
-@installer    It then builds the native engine's models in d4r/engine from those DLLs ([Engine] under
-@installer    Settings): Ray Reconstruction D, E and F straight from nvngx_dlssd.dll, and Super Resolution
-@installer    K, M and L (with their LDR variants) by rendering one test frame per model through d4r under
-@installer    GE-Proton 11, found in Steam's compatibility tools (or set D4R_PROTON=/path/to/GE-Proton11-3).
-@installer    The first time this takes a few minutes while DLSS's kernels compile. --no-engine skips it;
-@installer    bash install.sh --engine-only builds the models later, --rebuild-engine builds them again.
-@clean 2. Copy nvngx_dlss.dll into the d4r folder, and _nvngx.dll into d4r/ngx.
+@installer    Verified copies are kept in ~/.cache/d4r/nvidia, so installing d4r in the next game needs no
+@installer    download. install.sh then asks whether to set up d4r's own DLSS engine (recommended: faster,
+@installer    lower latency). That builds the engine's models in d4r/engine from the DLLs: Ray Reconstruction
+@installer    D, E and F straight from nvngx_dlssd.dll, and Super Resolution K, M and L (with their LDR
+@installer    variants) by rendering one test frame per model through d4r under GE-Proton 11, found in Steam's
+@installer    compatibility tools (or set D4R_PROTON=/path/to/GE-Proton11-3). It takes a minute or two once;
+@installer    the models are kept in ~/.cache/d4r/engine-models for the next game. bash install.sh --help lists
+@installer    options for scripted installs.
 @installer 3. In Steam, open the game's Properties:
 @clean 3. In Steam, open the game's Properties:
 @full 2. In Steam, open the game's Properties:
@@ -107,9 +108,10 @@ Settings
   PreferAccuracy = true. This uses original translated enc1/enc2 layers while retaining other
   native acceleration. It reduced trails in a captured Townfall sequence on RX 7700 XT and costs
   some GPU time. Restart after changing it; other scenes and RDNA4 hardware still need testing.
-- [Engine] Enabled = true (experimental, off by default) runs DLSS 4 (K), 4.5 (M and L) and Ray
-  Reconstruction (D, E and F) on d4r's own Vulkan inference engine: the work is recorded into the game's
-  own frame instead of going through CUDA emulation. It needs Mesa RADV with VK_KHR_cooperative_matrix
+- [Engine] runs DLSS 4 (K), 4.5 (M and L) and Ray Reconstruction (D, E and F) on d4r's own Vulkan
+  inference engine: the work is recorded into the game's own frame instead of going through CUDA
+  emulation, which is faster. Enabled = auto (the default) uses it whenever its models are in d4r/engine;
+  true / false force it on / off. It needs Mesa RADV with VK_KHR_cooperative_matrix
   and the models in d4r/engine: k (K), k-ldr (K in games without HDR), m and m-ldr (M), l and l-ldr (L),
   rr-d, rr-e and rr-f (Ray Reconstruction). Games and settings it does not cover (other models,
   display-resolution motion vectors with L or M) keep using the normal path,
@@ -197,7 +199,7 @@ Uninstall
 ---------
 Delete dxgi.dll, OptiScaler.ini, OptiScaler.log (if present), d3d12.dll, d3d12core.dll,
 D4R_README.txt, install.sh (if present) and the d4r folder from the game folder, and clear the launch options. The kernel
-cache in ~/.cache/d4r can be deleted too.
+cache in ~/.cache/d4r can be deleted too; it also holds install.sh's copies of the NVIDIA DLLs and the engine models.
 
 
 Licenses
diff --git a/packaging/build_engine_models.sh b/packaging/build_engine_models.sh
index 525651f..f5baa7b 100755
--- a/packaging/build_engine_models.sh
+++ b/packaging/build_engine_models.sh
@@ -2,7 +2,8 @@
 # Builds the native engine's models ([Engine] in d4r.ini) on this machine, from the NVIDIA DLLs install.sh put in
 # the d4r folder. Shipped as d4r/tools/build-engine-models.sh; install.sh runs it.
 #
-# usage: bash d4r/tools/build-engine-models.sh [--rr-only | --sr-only] [D4R_FOLDER]
+# usage: bash d4r/tools/build-engine-models.sh [--rr-only | --sr-only] [--exact] [D4R_FOLDER]
+#        bash d4r/tools/build-engine-models.sh --find-proton      prints the GE-Proton it would use (or nothing)
 #
 #   Ray Reconstruction  engine/rr-d, rr-e, rr-f   from d4r/nvngx_dlssd.dll 310.9.1 alone (about half a minute)
 #   Super Resolution    engine/k, k-ldr, m, m-ldr, l, l-ldr
@@ -11,19 +12,41 @@
 #                       GE-Proton, and the uploads are saved (a minute or two each; the first run also compiles
 #                       DLSS's kernels and creates a temporary Proton prefix)
 # Needs python3 with numpy, and for Super Resolution a GE-Proton (D4R_PROTON=/path/to/GE-Proton11-3 to choose one).
+# The models are the fastest builds (this GPU's own arithmetic; engine/README.md). --exact builds NVIDIA's roundings
+# instead: bit-identical to the CUDA path, about 20% slower (K is the same either way).
 # Everything written is derived from NVIDIA's DLLs: it stays in this folder and must not be redistributed.
 set -euo pipefail
 
 fail() { printf 'build-engine-models: %s\n' "$*" >&2; exit 1; }
-DO_RR=1 DO_SR=1
+DO_RR=1 DO_SR=1 FIND_PROTON=0
 while [[ $# -gt 0 ]]; do
   case "$1" in
     --rr-only) DO_SR=0; shift ;;
     --sr-only) DO_RR=0; shift ;;
-    -h|--help) sed -n '2,15p' "${BASH_SOURCE[0]}" | sed 's/^# \{0,1\}//'; exit 0 ;;
+    --exact) export D4R_RR_RELAXED=0 M_EXACT=1; shift ;;
+    --find-proton) FIND_PROTON=1; shift ;;
+    -h|--help) sed -n '2,19p' "${BASH_SOURCE[0]}" | sed 's/^# \{0,1\}//'; exit 0 ;;
     *) break ;;
   esac
 done
+find_proton() {
+  # a GE-Proton: D4R_PROTON, else GE-Proton11-3 (the tested one), else the newest stock GE-Proton11-N in Steam's
+  # compatibility tools. Renamed or rebuilt variants (2026-10-14: one with a suffix after the version number) can
+  # fail NGX's CUDA initialisation, so they are only used when named.
+  PROTON="${D4R_PROTON:-}"
+  if [[ -z "$PROTON" ]]; then
+    best=-1
+    for d in "$HOME/.local/share/Steam" "$HOME/.steam/root" "$HOME/.steam/steam" \
+             "$HOME/.var/app/com.valvesoftware.Steam/data/Steam"; do
+      for p in "$d"/compatibilitytools.d/GE-Proton11-*; do
+        n="${p##*/GE-Proton11-}"
+        [[ -x "$p/proton" && "$n" =~ ^[0-9]+$ ]] || continue
+        if [[ "$n" == 3 ]]; then best=1000; PROTON="$p"; elif (( n > best )); then best=$n; PROTON="$p"; fi
+      done
+    done
+  fi
+}
+if (( FIND_PROTON )); then find_proton; [[ -z "$PROTON" ]] || printf '%s\n' "$PROTON"; exit 0; fi
 TOOLS="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 KIT="$TOOLS/models"
 RUNTIME="$(cd -- "${1:-$TOOLS/..}" && pwd)"
@@ -82,21 +105,7 @@ if (( DO_SR )); then
   DLL="$RUNTIME/nvngx_dlss.dll"
   [[ -f "$DLL" && "$(sha "$DLL")" == "$DLSS_SHA256" ]] || fail "Super Resolution models need nvngx_dlss.dll 310.7.0 in $RUNTIME (run install.sh)"
   [[ -f "$RUNTIME/ngx/_nvngx.dll" ]] || fail "missing $RUNTIME/ngx/_nvngx.dll (run install.sh)"
-  # a GE-Proton: D4R_PROTON, else GE-Proton11-3 (the tested one), else the newest stock GE-Proton11-N in Steam's
-  # compatibility tools. Renamed or rebuilt variants (2026-10-14: one with a suffix after the version number) can
-  # fail NGX's CUDA initialisation, so they are only used when named.
-  PROTON="${D4R_PROTON:-}"
-  if [[ -z "$PROTON" ]]; then
-    best=-1
-    for d in "$HOME/.local/share/Steam" "$HOME/.steam/root" "$HOME/.steam/steam" \
-             "$HOME/.var/app/com.valvesoftware.Steam/data/Steam"; do
-      for p in "$d"/compatibilitytools.d/GE-Proton11-*; do
-        n="${p##*/GE-Proton11-}"
-        [[ -x "$p/proton" && "$n" =~ ^[0-9]+$ ]] || continue
-        if [[ "$n" == 3 ]]; then best=1000; PROTON="$p"; elif (( n > best )); then best=$n; PROTON="$p"; fi
-      done
-    done
-  fi
+  find_proton
   [[ -n "$PROTON" && -x "$PROTON/proton" ]] ||
     fail 'no GE-Proton found: set D4R_PROTON=/path/to/GE-Proton11-3 (the folder holding the proton script)'
   STEAM_ROOT="$(dirname -- "$(dirname -- "$PROTON")")"
diff --git a/packaging/d4r.ini b/packaging/d4r.ini
index 0acb400..16cd1f5 100644
--- a/packaging/d4r.ini
+++ b/packaging/d4r.ini
@@ -29,7 +29,7 @@ ShowWatermark = false
 Enable = auto
 ; Independent denoiser presets: auto (game choice), default, D, E (transformer) or F (DLSS 4.5).
 ; E and F through NVIDIA's library need a denoiser DLL containing that model (F: 310.9 or later). On the engine
-; ([Engine] Enabled = true) F runs from the model in d4r\engine\rr-f; frames the library serves instead show
+; ([Engine]) F runs from the model in d4r\engine\rr-f; frames the library serves instead show
 ; preset D when the DLL is older (d4r_nvngx.log says so).
 Model = auto
 
@@ -73,11 +73,13 @@ ElideNgxSync = true
 DirectOutput = auto
 
 [Engine]
-; Experimental. Runs DLSS 4 and 4.5 (models K, L and M) on d4r's own Vulkan inference engine instead of NVIDIA's
-; kernels: the game shows the result of the frame it just rendered and [Latency] / [Interop] do not apply.
-; Needs Mesa RADV with VK_KHR_cooperative_matrix and the models in d4r\engine\k, k-ldr, m, m-ldr, l and l-ldr
-; (see D4R_README.txt). Games or settings it does not cover use the normal path; d4r_nvngx.log says why.
-Enabled = false
+; Runs DLSS 4 and 4.5 (models K, L and M) and Ray Reconstruction (D, E and F) on d4r's own Vulkan inference
+; engine instead of NVIDIA's kernels: the faster path, and the game shows the result of the frame it just rendered
+; ([Latency] / [Interop] do not apply). Needs Mesa RADV with VK_KHR_cooperative_matrix and the models install.sh
+; builds in d4r\engine (k, k-ldr, m, m-ldr, l, l-ldr, rr-d, rr-e, rr-f). Games or settings it does not cover,
+; and a device that cannot run it, use the normal path; d4r_nvngx.log says why.
+; auto = on when d4r\engine holds a model, true / false = always / never.
+Enabled = auto
 ; Another model K folder for games with the HDR flag (a path relative to the d4r folder, or a Windows path
 ; such as Z:\home\me\k)
 ModelDir = auto
diff --git a/tools/d4r_nvngx_shim.cpp b/tools/d4r_nvngx_shim.cpp
index 3f2368d..3497e0b 100644
--- a/tools/d4r_nvngx_shim.cpp
+++ b/tools/d4r_nvngx_shim.cpp
@@ -695,8 +695,25 @@ static void load_portable_config()
     // release cannot ship that kernel, which is built from NVIDIA's PTX.
     portable_set("D4R_SHIM_OUTPUT_DIRECT", ini_flag(ini, "interop", "DirectOutput", nativeOn) ? "1" : "0");
 
-    // [Engine]: d4r's own Vulkan inference for DLSS 4 (K); the model is looked up in d4r\engine\k
-    portable_set("D4R_ENGINE", ini_flag(ini, "engine", "Enabled", 0) ? "1" : "0");
+    // [Engine]: d4r's own Vulkan inference (K, L, M and Ray Reconstruction); the models are looked up in d4r\engine.
+    // Enabled = auto (the default) runs it when install.sh built a model there: it is the faster path, and a model
+    // the device cannot run, or a feature no model covers, still goes to the CUDA backend (d4r_nvngx.log says why).
+    {
+        const std::string enabled = ascii_lower(ini_value(ini, "engine", "Enabled"));
+        bool on = false;
+        if (enabled.empty() || enabled == "auto")
+        {
+            for (const wchar_t* model : {L"k", L"k-ldr", L"m", L"m-ldr", L"l", L"l-ldr", L"rr-d", L"rr-e", L"rr-f"})
+            {
+                const DWORD attributes = GetFileAttributesW((dir + L"\\engine\\" + model).c_str());
+                if (attributes != INVALID_FILE_ATTRIBUTES && (attributes & FILE_ATTRIBUTE_DIRECTORY))
+                    on = true;
+            }
+        }
+        else
+            on = ini_flag(ini, "engine", "Enabled", 0) != 0;
+        portable_set("D4R_ENGINE", on ? "1" : "0");
+    }
     if (const std::string engineModel = ini_value(ini, "engine", "ModelDir"); !engineModel.empty())
         portable_set(L"D4R_ENGINE_MODEL_DIR", portable_path(engineModel));
     // Network: the network on the engine's Vulkan shader ("vulkan", and the default: "auto") or on the native HIP