diff --git a/.env.example b/.env.example
index c6a152c..5199a4d 100644
--- a/.env.example
+++ b/.env.example
@@ -26,3 +26,18 @@
 # --- Periodic batch glean ---
 # Seconds between automatic glean runs from sources.yaml. Set to 0 to disable.
 # TURNSTONE_GLEAN_INTERVAL=900
+
+# --- Multi-agent diagnose pipeline (experimental) ---
+# Enable the 5-stage ML pipeline instead of the single-LLM summarize() call.
+# TURNSTONE_MULTI_AGENT_DIAGNOSE=true
+
+# Stage 2 — ML severity classifier (optional; falls back to pattern_tags then regex).
+# Recommended: byviz/bylastic_classification_logs (~300MB, downloaded from HuggingFace)
+# TURNSTONE_CLASSIFIER_MODEL=byviz/bylastic_classification_logs
+
+# Stage 4 — Embedding backend for false-positive suppression.
+# sentence_transformers: in-process local model (downloads on first use)
+# ollama: uses a running Ollama instance (no download needed if model is already pulled)
+# TURNSTONE_EMBED_BACKEND=sentence_transformers
+# TURNSTONE_EMBED_MODEL=BAAI/bge-small-en-v1.5
+# TURNSTONE_EMBED_DEVICE=cpu
diff --git a/app/services/diagnose/pipeline.py b/app/services/diagnose/pipeline.py
index a60952f..6539b8f 100644
--- a/app/services/diagnose/pipeline.py
+++ b/app/services/diagnose/pipeline.py
@@ -5,10 +5,17 @@ from __future__ import annotations
 import asyncio
 import dataclasses
 import logging
+import os
 from collections.abc import AsyncGenerator
 from pathlib import Path
 from typing import Any
 
+# Optional ML classifier model for Stage 2.
+# When empty (default), Stage 2 falls back to pattern_tags then regex.
+# Set TURNSTONE_CLASSIFIER_MODEL to a HuggingFace model ID to enable ML classification.
+# Recommended: byviz/bylastic_classification_logs (DistilBERT, ~300MB)
+_CLASSIFIER_MODEL: str = os.environ.get("TURNSTONE_CLASSIFIER_MODEL", "")
+
 from app.context.retriever import RetrievedContext
 from app.services.diagnose.classifier import SeverityClassifier
 from app.services.diagnose.hypothesizer import RootCauseHypothesizer
@@ -74,7 +81,7 @@ async def run_pipeline(
     # Stage 2: Severity classification
     try:
         classified = await asyncio.to_thread(
-            SeverityClassifier().classify, timeline
+            SeverityClassifier(model_id=_CLASSIFIER_MODEL).classify, timeline
         )
     except Exception as exc:
         logger.exception("Stage 2 (classifier) failed: %s", exc)