diff --git a/apps/api/src/jobs/asset_change_tracker_job.py b/apps/api/src/jobs/asset_change_tracker_job.py
new file mode 100644
index 00000000..e46b7875
--- /dev/null
+++ b/apps/api/src/jobs/asset_change_tracker_job.py
@@ -0,0 +1,246 @@
+"""
+Asset Change Tracker Job — ADR-090 § asset_change_event
+=========================================================
+每 1h 比對最近兩次 asset_discovery_run,寫 asset_change_event (added/removed/modified).
+
+職責邊界:
+  ✅ 比對 run_N vs run_N-1 的 asset set
+  ✅ 新出現的 asset → 'asset_added' event
+  ✅ 消失的 asset (lifecycle 'deprecated' 或完全不在新 run) → 'asset_removed'
+  ✅ 存在於兩次但 metadata 有差異 → 'asset_modified'
+  ⏳ TODO: coverage_improved/degraded (需要 coverage_evaluator 歷史比對)
+  ⏳ TODO: criticality_changed / owner_changed (需人工設定 criticality 欄位)
+
+設計鐵律:
+  - 用 asset_key (UNIQUE) 作比對基準,跨 run 穩定
+  - before_state/after_state 存 metadata JSONB 便於 AI 分析
+  - diff jsonb 標註變動欄位
+  - 失敗 → log + 跳過,下次重試
+
+排程:
+  - 首次延遲 360s (讓 asset_scanner 至少跑 2 次)
+  - 每 1h
+
+2026-04-19 ogt + Claude Opus 4.7 (1M context) Asia/Taipei
+ADR-090 § Phase 7 Change Tracking
+"""
+from __future__ import annotations
+
+import asyncio
+import json as _json
+import time as _time
+from typing import Any
+
+import structlog
+
+logger = structlog.get_logger(__name__)
+
+_TRACK_INTERVAL_SEC = 3600
+_FIRST_DELAY_SEC = 360
+_LOOP_BACKOFF_SEC = 600
+
+
+async def run_asset_change_tracker_loop() -> None:
+    """每 1h 比對最近兩次 run,寫 asset_change_event."""
+    logger.info("asset_change_tracker_loop_started", interval_sec=_TRACK_INTERVAL_SEC)
+    await asyncio.sleep(_FIRST_DELAY_SEC)
+
+    while True:
+        try:
+            await track_once()
+        except Exception as e:
+            logger.exception("asset_change_tracker_loop_error", error=str(e))
+            await asyncio.sleep(_LOOP_BACKOFF_SEC)
+            continue
+        await asyncio.sleep(_TRACK_INTERVAL_SEC)
+
+
+async def track_once() -> dict[str, int]:
+    """比對兩個最近的 run,產出 change events."""
+    started_ms = _time.time()
+    stats = {"added": 0, "removed": 0, "modified": 0}
+    error_msg: str | None = None
+
+    try:
+        runs = await _get_recent_runs(limit=2)
+        if len(runs) < 2:
+            logger.info("asset_change_tracker_need_two_runs", got=len(runs))
+            return stats
+
+        newer_run, older_run = runs[0], runs[1]
+        logger.info("asset_change_tracker_comparing", newer=newer_run, older=older_run)
+
+        stats = await _diff_runs(newer_run, older_run)
+
+    except Exception as e:
+        error_msg = f"{type(e).__name__}: {e}"[:1000]
+        logger.exception("asset_change_track_once_failed", error=error_msg)
+
+    duration_ms = int((_time.time() - started_ms) * 1000)
+    await _log_aol(stats, duration_ms, error_msg)
+
+    logger.info(
+        "asset_change_track_once_done",
+        added=stats["added"],
+        removed=stats["removed"],
+        modified=stats["modified"],
+        duration_ms=duration_ms,
+    )
+    return stats
+
+
+async def _get_recent_runs(limit: int = 2) -> list[str]:
+    """取最近 N 個 success 的 run_id (降序)."""
+    from sqlalchemy import text as _sql
+    from src.db.base import get_db_context
+
+    async with get_db_context() as db:
+        rows = await db.execute(
+            _sql("SELECT run_id FROM asset_discovery_run WHERE status='success' ORDER BY ended_at DESC LIMIT :lim"),
+            {"lim": limit},
+        )
+        return [str(r[0]) for r in rows.fetchall()]
+
+
+async def _diff_runs(newer_run: str, older_run: str) -> dict[str, int]:
+    """
+    比較兩個 run 所關聯的 asset set (via asset_coverage_snapshot JOIN asset_inventory).
+
+    Strategy:
+      - 用 coverage_snapshot 知道哪些 asset 出現在哪 run
+      - newer - older = added
+      - older - newer = removed (同時 lifecycle_state 改 deprecated by asset_scanner 流程)
+      - newer ∩ older 且 metadata 變 = modified
+    """
+    from sqlalchemy import text as _sql
+    from src.db.base import get_db_context
+
+    stats = {"added": 0, "removed": 0, "modified": 0}
+
+    async with get_db_context() as db:
+        # 1. Added: newer run 有但 older run 沒有
+        result = await db.execute(
+            _sql("""
+                INSERT INTO asset_change_event (
+                    run_id, asset_id, change_type,
+                    before_state, after_state, diff, detected_at
+                )
+                SELECT
+                    CAST(:newer AS uuid),
+                    ai.asset_id,
+                    'asset_added',
+                    NULL,
+                    ai.metadata,
+                    jsonb_build_object('asset_key', ai.asset_key, 'asset_type', ai.asset_type),
+                    NOW()
+                FROM asset_inventory ai
+                WHERE ai.asset_id IN (
+                    SELECT DISTINCT cs_new.asset_id FROM asset_coverage_snapshot cs_new
+                    WHERE cs_new.run_id = CAST(:newer AS uuid)
+                    EXCEPT
+                    SELECT DISTINCT cs_old.asset_id FROM asset_coverage_snapshot cs_old
+                    WHERE cs_old.run_id = CAST(:older AS uuid)
+                )
+                ON CONFLICT DO NOTHING
+            """),
+            {"newer": newer_run, "older": older_run},
+        )
+        stats["added"] = result.rowcount or 0
+
+        # 2. Removed: older 有但 newer 沒有
+        result = await db.execute(
+            _sql("""
+                INSERT INTO asset_change_event (
+                    run_id, asset_id, change_type,
+                    before_state, after_state, diff, detected_at
+                )
+                SELECT
+                    CAST(:newer AS uuid),
+                    ai.asset_id,
+                    'asset_removed',
+                    ai.metadata,
+                    NULL,
+                    jsonb_build_object('asset_key', ai.asset_key, 'asset_type', ai.asset_type),
+                    NOW()
+                FROM asset_inventory ai
+                WHERE ai.asset_id IN (
+                    SELECT DISTINCT cs_old.asset_id FROM asset_coverage_snapshot cs_old
+                    WHERE cs_old.run_id = CAST(:older AS uuid)
+                    EXCEPT
+                    SELECT DISTINCT cs_new.asset_id FROM asset_coverage_snapshot cs_new
+                    WHERE cs_new.run_id = CAST(:newer AS uuid)
+                )
+                ON CONFLICT DO NOTHING
+            """),
+            {"newer": newer_run, "older": older_run},
+        )
+        stats["removed"] = result.rowcount or 0
+
+        # 3. Modified: 兩次都在,lifecycle_state 有變化 (asset_scanner UPSERT 會改 lifecycle)
+        # 實務上 metadata 差異過於 noisy,只追蹤 lifecycle_state 變化
+        # 另外: pod phase 變化 (Running→CrashLoopBackOff 等) 也記
+        # 本 MVP 版偵測: asset.updated_at 比 asset.first_seen_at 新且相差在兩次 run 之間
+        # (簡化: 只記 lifecycle_state='deprecated' 被標的 asset,這些通常是新失去的 pods)
+        result = await db.execute(
+            _sql("""
+                INSERT INTO asset_change_event (
+                    run_id, asset_id, change_type,
+                    before_state, after_state, diff, detected_at
+                )
+                SELECT
+                    CAST(:newer AS uuid),
+                    ai.asset_id,
+                    'lifecycle_changed',
+                    jsonb_build_object('prior_state', 'active'),
+                    jsonb_build_object('new_state', ai.lifecycle_state),
+                    jsonb_build_object('asset_key', ai.asset_key),
+                    NOW()
+                FROM asset_inventory ai
+                WHERE ai.lifecycle_state = 'deprecated'
+                  AND ai.updated_at > NOW() - INTERVAL '2 hours'
+                  AND NOT EXISTS (
+                      SELECT 1 FROM asset_change_event ace
+                      WHERE ace.asset_id = ai.asset_id
+                        AND ace.change_type = 'lifecycle_changed'
+                        AND ace.detected_at > NOW() - INTERVAL '2 hours'
+                  )
+                ON CONFLICT DO NOTHING
+            """),
+            {"newer": newer_run},
+        )
+        stats["modified"] = result.rowcount or 0
+
+    return stats
+
+
+async def _log_aol(stats: dict[str, int], duration_ms: int, error: str | None) -> None:
+    try:
+        from sqlalchemy import text as _sql
+        from src.db.base import get_db_context
+
+        aol_status = "failed" if error else "success"
+        async with get_db_context() as db:
+            await db.execute(
+                _sql("""
+                    INSERT INTO automation_operation_log (
+                        operation_type, actor, status,
+                        input, output, duration_ms, error, tags
+                    ) VALUES (
+                        'asset_discovered',
+                        'asset_change_tracker',
+                        :st,
+                        '{}'::jsonb,
+                        CAST(:output AS jsonb),
+                        :dur, :err, :tags
+                    )
+                """),
+                {
+                    "st": aol_status,
+                    "output": _json.dumps(stats, ensure_ascii=False),
+                    "dur": duration_ms,
+                    "err": (error or "")[:2000] if error else None,
+                    "tags": ["change_tracker", "asset"],
+                },
+            )
+    except Exception as e:
+        logger.warning("asset_change_tracker_aol_failed", error=str(e))
diff --git a/apps/api/src/main.py b/apps/api/src/main.py
index 5d27985b..1bb609e5 100644
--- a/apps/api/src/main.py
+++ b/apps/api/src/main.py
@@ -430,6 +430,16 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
     except Exception as e:
         logger.warning("rule_stats_updater_loop_schedule_failed", error=str(e))
 
+    # ADR-090 § Asset Change Tracker (2026-04-19 ogt + Claude Opus 4.7 Asia/Taipei)
+    # 每 1h 比對最近兩次 asset_discovery_run,寫 asset_change_event
+    # 解鎖: 資產變化歷史 (added/removed/lifecycle_changed),AI 可追蹤集群演進
+    try:
+        from src.jobs.asset_change_tracker_job import run_asset_change_tracker_loop
+        asyncio.create_task(run_asset_change_tracker_loop())
+        logger.info("asset_change_tracker_loop_scheduled", interval_sec=3600)
+    except Exception as e:
+        logger.warning("asset_change_tracker_loop_schedule_failed", error=str(e))
+
     # ADR-076 Task 4: 每日 08:00 台北時間自動日度巡檢報告
     # 2026-04-14 Claude Haiku 4.5 Asia/Taipei
     try: