diff --git a/docs/MAC.md b/docs/MAC.md
index d63b1f8..319d953 100644
--- a/docs/MAC.md
+++ b/docs/MAC.md
@@ -118,3 +118,66 @@ Set `MODEL_FILE` in `.env` to a different GGUF in `models/` and restart. The bun
 `templates/chat_template.jinja` is **Qwen3.6-specific**; for a non-Qwen GGUF set
 `CHAT_TEMPLATE_FILE` to that model's own Jinja template (a wrong template silently corrupts
 tool-calling).
+
+## Alternative backend: MLX (faster prefill)
+
+`scripts/mac-run.sh` can serve `:8080` with Apple's **mlx-lm** instead of llama.cpp, behind a
+`BACKEND` knob. It's opt-in; the default stays llama.cpp.
+
+```bash
+BACKEND=mlx bash scripts/mac-run.sh      # or set BACKEND=mlx in .env
+```
+
+On an M3 Pro / 36 GB serving the 4-bit MLX model, prefill is ~530 tok/s vs llama.cpp's ~90 (**~6x**),
+with decode at or above the MTP path (~39 vs ~37 tok/s). Prefill is what the compaction loop is bound
+by, so this is the win that matters for long jobs. Greedy output matches llama.cpp (9/10 exact, the
+lone diff a synonym).
+
+| Backend | Engine | Model | Prefill | Context ceiling |
+| --- | --- | --- | --- | --- |
+| `llamacpp` *(default)* | llama.cpp (Metal, GGUF) | `models/mtp/...Q4_K_XL.gguf` | ~90 tok/s | >128K (stable) |
+| `mlx` | mlx-lm (`mlx_lm.server`) | `models/mlx/Qwen3.6-35B-A3B-UD-MLX-4bit` | ~530 tok/s | ~75K (auto-capped) |
+
+Use `llamacpp` for jobs that need >75K context; use `mlx` for throughput on the compaction-heavy
+loop and jobs under that cap.
+
+### MLX setup (one-time)
+
+mlx-lm must live in its **own** venv - installing it into the app `.venv` bumps `transformers` and
+breaks the embedder.
+
+```bash
+uv venv .venv-mlx
+VIRTUAL_ENV=$PWD/.venv-mlx uv pip install mlx-lm
+# Download or convert a 4-bit MLX build into models/mlx/Qwen3.6-35B-A3B-UD-MLX-4bit
+# (e.g. mlx_lm.convert, or pull a pre-quantized 4-bit MLX repo).
+```
+
+`mac-run.sh` checks both the venv and the model exist before starting and errors with the fix if not.
+
+### MLX env knobs
+
+| Var | Default | Meaning |
+| --- | --- | --- |
+| `BACKEND` | `llamacpp` | `llamacpp` or `mlx`. |
+| `MLX_MODEL` | `models/mlx/Qwen3.6-35B-A3B-UD-MLX-4bit` | Path to the MLX model dir. |
+| `MLX_CTX_CAP` | `75000` | Max context for MLX; `CTX_SIZE` is auto-capped to this. |
+| `MODEL_ID` | (auto = `MLX_MODEL`) | Pinned so Pi's requests match the loaded model (see below). |
+
+### MLX caveats
+
+- **Context auto-cap.** Stock `mlx_lm.server` runs an **fp16 KV cache** (no `--kv-bits` flag -
+  upstream [ml-explore/mlx-lm#1043](https://github.com/ml-explore/mlx-lm/issues/1043)). fp16 KV
+  OOMs (`kIOGPUCommandBufferCallbackErrorOutOfMemory`) at ~78-92K actual tokens on 36 GB, so the
+  script caps context to `MLX_CTX_CAP` (75K). Quantized KV is greedy-lossless with 15/15 fact
+  recall at 83.5K locally; once the upstream server gains `--kv-bits`, switch it on and raise the
+  cap toward ~85K (kv4 ceiling ~92-113K).
+- **`MODEL_ID` is pinned to the model path.** `mlx_lm.server` resolves the request's `model` field
+  against the loaded model and otherwise tries to fetch it from HuggingFace (a request for the
+  friendly label `qwen3.6` -> 404). llama.cpp ignores the label; MLX needs the match, so the script
+  exports `MODEL_ID=$MLX_MODEL` for this backend.
+- **Dashboard tok/s + KV gauge are llama.cpp-only.** They read llama.cpp's `/metrics` and `/slots`,
+  which `mlx_lm.server` doesn't expose, so those live widgets stay blank under `mlx` (the job still
+  runs and packages normally).
+
+Stop the MLX model with `pkill -f mlx_lm.server`.
diff --git a/scripts/mac-run.sh b/scripts/mac-run.sh
index 4e55da9..ba596c5 100755
--- a/scripts/mac-run.sh
+++ b/scripts/mac-run.sh
@@ -7,6 +7,10 @@
 # The Pi agent and the v5-nano embedder run inside the app process tree (embedder on CPU).
 # See docs/MAC.md for the full setup. This script only LAUNCHES; install steps live there.
 #
+# BACKEND selects the :8080 server: 'llamacpp' (default, GGUF via llama.cpp) or 'mlx' (mlx-lm,
+# Apple-native, ~6x faster prefill). mlx uses .venv-mlx + models/mlx/... and auto-caps context to
+# MLX_CTX_CAP (fp16-KV OOM headroom). See docs/MAC.md.
+#
 # It honours the same env knobs as the docker-compose path (MODEL_FILE, CTX_SIZE, SPEC_ARGS,
 # CHAT_TEMPLATE_FILE), just with Mac-appropriate defaults:
 #   - SPEC_ARGS defaults to '--spec-type draft-mtp --spec-draft-n-max 2' (measured ~1.23x
@@ -26,9 +30,18 @@ if [ -z "$JINA_API_KEY" ] || [ "$JINA_API_KEY" = "jina_xxxx" ]; then
   exit 1
 fi
 
-command -v llama-server >/dev/null || { echo "ERROR: llama-server not found. Install: brew install llama.cpp" >&2; exit 1; }
+# Inference backend: llamacpp (GGUF via llama.cpp, default) | mlx (mlx-lm, Apple-native).
+BACKEND="${BACKEND:-llamacpp}"
+
 [ -x "$ROOT/.venv/bin/python" ] || { echo "ERROR: .venv missing. See docs/MAC.md (uv venv + uv pip install)." >&2; exit 1; }
 command -v pi >/dev/null || { echo "ERROR: pi not found. Install: npm install -g @earendil-works/pi-coding-agent@0.78.0" >&2; exit 1; }
+case "$BACKEND" in
+  llamacpp)
+    command -v llama-server >/dev/null || { echo "ERROR: llama-server not found. Install: brew install llama.cpp" >&2; exit 1; } ;;
+  mlx)
+    [ -x "$ROOT/.venv-mlx/bin/mlx_lm.server" ] || { echo "ERROR: .venv-mlx is missing mlx-lm. Create it: uv venv .venv-mlx && VIRTUAL_ENV=\$PWD/.venv-mlx uv pip install mlx-lm  (see docs/MAC.md)" >&2; exit 1; } ;;
+  *) echo "ERROR: BACKEND must be 'llamacpp' or 'mlx' (got '$BACKEND')" >&2; exit 1 ;;
+esac
 
 MODEL_FILE="${MODEL_FILE:-mtp/Qwen3.6-35B-A3B-UD-Q4_K_XL.gguf}"
 CTX_SIZE="${CTX_SIZE:-65536}"
@@ -36,7 +49,39 @@ NGL="${NGL:-999}"
 SPEC_ARGS="${SPEC_ARGS:---spec-type draft-mtp --spec-draft-n-max 2}"   # ~1.23x on Metal; set SPEC_ARGS= to disable
 CHAT_TEMPLATE_FILE="${CHAT_TEMPLATE_FILE:-$ROOT/templates/chat_template.jinja}"
 MODEL_PATH="$ROOT/models/$MODEL_FILE"
-[ -f "$MODEL_PATH" ] || { echo "ERROR: model not found: $MODEL_PATH  (see docs/MAC.md to download the GGUF)" >&2; exit 1; }
+
+# --- MLX backend knobs (only used when BACKEND=mlx) ---
+MLX_MODEL="${MLX_MODEL:-$ROOT/models/mlx/Qwen3.6-35B-A3B-UD-MLX-4bit}"
+# KV cache quantization. Stock mlx_lm.server ran fp16 KV (OOM ~78-92K actual tokens on a 36GB
+# Mac). The --kv-bits flag (ml-explore/mlx-lm#1353) pushes the ceiling to ~92-113K with 4-bit KV
+# (greedy-lossless, long-ctx recall verified). We auto-detect the flag below: when present we
+# default to 4-bit KV and the higher context cap; otherwise fp16 KV with the conservative cap.
+MLX_KV_BITS="${MLX_KV_BITS:-4}"
+MLX_KV_GROUP_SIZE="${MLX_KV_GROUP_SIZE:-64}"
+MLX_KV_ARGS=()
+
+if [ "$BACKEND" = "mlx" ]; then
+  [ -d "$MLX_MODEL" ] || { echo "ERROR: MLX model not found: $MLX_MODEL  (convert with mlx_lm.convert; see docs/MAC.md)" >&2; exit 1; }
+  # mlx_lm.server resolves the request's `model` field against the loaded model (and otherwise
+  # tries to fetch it from HuggingFace). llama.cpp ignores the label, but MLX needs it to match
+  # the loaded path, so pin Pi's MODEL_ID to it. (llama.cpp keeps the friendly default.)
+  export MODEL_ID="${MODEL_ID:-$MLX_MODEL}"
+  # Use quantized KV only if this mlx_lm.server build supports it; raise the cap accordingly.
+  if [ -n "$MLX_KV_BITS" ] && "$ROOT/.venv-mlx/bin/mlx_lm.server" --help 2>/dev/null | grep -q -- '--kv-bits'; then
+    MLX_KV_ARGS=(--kv-bits "$MLX_KV_BITS" --kv-group-size "$MLX_KV_GROUP_SIZE")
+    MLX_CTX_CAP="${MLX_CTX_CAP:-85000}"
+    echo "NOTE: BACKEND=mlx using ${MLX_KV_BITS}-bit KV (group $MLX_KV_GROUP_SIZE); ctx cap $MLX_CTX_CAP"
+  else
+    MLX_CTX_CAP="${MLX_CTX_CAP:-75000}"
+    [ -n "$MLX_KV_BITS" ] && echo "NOTE: this mlx_lm.server lacks --kv-bits (need mlx-lm#1353); fp16 KV, ctx cap $MLX_CTX_CAP"
+  fi
+  if [ "$CTX_SIZE" -gt "$MLX_CTX_CAP" ]; then
+    echo "NOTE: BACKEND=mlx caps CTX_SIZE $CTX_SIZE -> $MLX_CTX_CAP"
+    CTX_SIZE="$MLX_CTX_CAP"
+  fi
+else
+  [ -f "$MODEL_PATH" ] || { echo "ERROR: model not found: $MODEL_PATH  (see docs/MAC.md to download the GGUF)" >&2; exit 1; }
+fi
 
 mkdir -p logs "${JOBS_DIR:-./data/jobs}"
 
@@ -45,9 +90,30 @@ export PATH="$ROOT/.venv/bin:$(dirname "$(command -v pi)"):$PATH"
 export PI_BIN="$(command -v pi)"
 export PI_SKIP_VERSION_CHECK=1
 
-# --- 1. llama-server (Metal) --------------------------------------------------
+# Wait for the :8080 server to answer /health, or tail its log and bail.
+wait_for_server() {
+  local label="$1" logf="$2"
+  echo -n "waiting for $label"
+  for i in $(seq 1 120); do
+    if curl -fsS "http://127.0.0.1:8080/health" >/dev/null 2>&1; then echo " ready"; return 0; fi
+    echo -n "."; sleep 2
+    [ "$i" = 120 ] && { echo " TIMEOUT"; tail -30 "$logf"; exit 1; }
+  done
+}
+
+# --- 1. inference server (:8080) ----------------------------------------------
 if curl -fsS "http://127.0.0.1:8080/health" >/dev/null 2>&1; then
-  echo "llama-server already up on :8080"
+  echo "inference server already up on :8080"
+elif [ "$BACKEND" = "mlx" ]; then
+  echo "=== starting mlx_lm.server (Metal) - loads ~19GB, first run ~30-60s ==="
+  nohup "$ROOT/.venv-mlx/bin/mlx_lm.server" \
+    --model "$MLX_MODEL" \
+    --host 127.0.0.1 --port 8080 \
+    --max-tokens 8192 \
+    ${MLX_KV_ARGS[@]+"${MLX_KV_ARGS[@]}"} \
+    > "$ROOT/logs/mlx.log" 2>&1 &
+  echo "mlx_lm.server PID: $!  (logs: logs/mlx.log)"
+  wait_for_server "mlx_lm.server" "$ROOT/logs/mlx.log"
 else
   echo "=== starting llama-server (Metal) - loads ~22GB, first run ~30-60s ==="
   # shellcheck disable=SC2086
@@ -67,12 +133,7 @@ else
     $SPEC_ARGS \
     > "$ROOT/logs/llama.log" 2>&1 &
   echo "llama-server PID: $!  (logs: logs/llama.log)"
-  echo -n "waiting for llama-server"
-  for i in $(seq 1 120); do
-    if curl -fsS "http://127.0.0.1:8080/health" >/dev/null 2>&1; then echo " ready"; break; fi
-    echo -n "."; sleep 2
-    [ "$i" = 120 ] && { echo " TIMEOUT"; tail -30 "$ROOT/logs/llama.log"; exit 1; }
-  done
+  wait_for_server "llama-server" "$ROOT/logs/llama.log"
 fi
 
 # --- 2. FastAPI app -----------------------------------------------------------
@@ -85,6 +146,16 @@ export PORT="${PORT:-8000}"
 
 echo "=== starting Dataroom app on :$PORT ==="
 echo "    web UI:     http://localhost:$PORT/"
-echo "    LLAMA_URL:  $LLAMA_URL    ctx=$CTX_SIZE    ngl=$NGL    embedder=$EMBED_DEVICE"
-[ -z "$SPEC_ARGS" ] && echo "    spec:       (disabled)" || echo "    spec:       $SPEC_ARGS"
+echo "    backend:    $BACKEND"
+if [ "$BACKEND" = "mlx" ]; then
+  echo "    LLAMA_URL:  $LLAMA_URL    ctx=$CTX_SIZE (cap $MLX_CTX_CAP)    model=$MLX_MODEL    embedder=$EMBED_DEVICE"
+  if [ ${#MLX_KV_ARGS[@]} -gt 0 ]; then
+    echo "    note:       ${MLX_KV_BITS}-bit KV (group $MLX_KV_GROUP_SIZE, mlx-lm#1353); dashboard tok/s + KV gauge are llama.cpp-only"
+  else
+    echo "    note:       fp16 KV (this mlx_lm.server lacks --kv-bits, see mlx-lm#1353); dashboard tok/s + KV gauge are llama.cpp-only"
+  fi
+else
+  echo "    LLAMA_URL:  $LLAMA_URL    ctx=$CTX_SIZE    ngl=$NGL    embedder=$EMBED_DEVICE"
+  [ -z "$SPEC_ARGS" ] && echo "    spec:       (disabled)" || echo "    spec:       $SPEC_ARGS"
+fi
 exec "$ROOT/.venv/bin/python" -m server.app