diff --git a/backend/app/api/admin.py b/backend/app/api/admin.py
index c33121a..3f77d9a 100644
--- a/backend/app/api/admin.py
+++ b/backend/app/api/admin.py
@@ -348,3 +348,15 @@ async def trigger_reextract_archives():
 
     async_result = reextract_archive_attachments_task.delay()
     return jsonify({"task_id": async_result.id, "status": "queued"}), 202
+
+
+@admin_bp.route("/maintenance/prune-predictions", methods=["POST"])
+async def trigger_prune_predictions():
+    """Operator-triggered #764 backfill: drop stored tagger predictions below
+    the current ml_settings.tagger_store_floor and clamp allowlist thresholds
+    up to it. Shrinks image_record's TOAST (~100 GB of sub-0.70 scores).
+    Idempotent + self-resuming; runs on the maintenance_long lane."""
+    from ..tasks.admin import prune_low_confidence_predictions_task
+
+    async_result = prune_low_confidence_predictions_task.delay()
+    return jsonify({"task_id": async_result.id, "status": "queued"}), 202
diff --git a/backend/app/tasks/admin.py b/backend/app/tasks/admin.py
index c6a1b08..7123a71 100644
--- a/backend/app/tasks/admin.py
+++ b/backend/app/tasks/admin.py
@@ -207,3 +207,99 @@ def rescan_series_suggestions_task(self, after_post_id: int = 0) -> dict:
         )
         rescan_series_suggestions_task.delay(summary["resume_after_id"])
     return summary
+
+
+@celery.task(
+    name="backend.app.tasks.admin.prune_low_confidence_predictions_task",
+    bind=True,
+    autoretry_for=(OperationalError, DBAPIError),
+    retry_backoff=15, retry_backoff_max=180, max_retries=1,
+    soft_time_limit=3600, time_limit=4200,  # 60 min / 70 min
+)
+def prune_low_confidence_predictions_task(self, after_id: int = 0) -> dict:
+    """One-time #764 backfill: drop tagger_predictions entries below the DB
+    store floor (ml_settings.tagger_store_floor) from existing image_record
+    rows, and clamp any allowlist min_confidence below the floor up to it.
+
+    The Camie tagger emits ~10k tags; the old 0.05 floor stored the entire
+    near-zero tail, bloating image_record's TOAST to ~100 GB. This rewrites
+    each row to the new floor. Keyset by id ASC (restart-safe via after_id);
+    idempotent — already-pruned rows rewrite to themselves and are skipped.
+    Rewriting rows generates bloat, so run VACUUM FULL / pg_repack on
+    image_record afterward to return the disk to the OS.
+
+    The keep predicate (confidence >= floor) mirrors Tagger.infer's store
+    gate so backfilled rows match what new imports store. Self-resumes on the
+    soft time limit (re-enqueues from the last committed id)."""
+    from celery.exceptions import SoftTimeLimitExceeded
+    from sqlalchemy import select, update
+
+    from ..models import ImageRecord, MLSettings, TagAllowlist
+
+    SessionLocal = _sync_session_factory()
+    scanned = 0
+    pruned = 0
+    clamped = 0
+    last_id = after_id
+    try:
+        with SessionLocal() as session:
+            floor = session.execute(
+                select(MLSettings.tagger_store_floor).where(MLSettings.id == 1)
+            ).scalar_one()
+            # Clamp allowlist thresholds below the new floor once, on the
+            # first pass (#764 consumer #4) — a sub-floor min_confidence can't
+            # apply more permissively now that nothing below it is stored.
+            if after_id == 0:
+                clamped = session.execute(
+                    update(TagAllowlist)
+                    .where(TagAllowlist.min_confidence < floor)
+                    .values(min_confidence=floor)
+                ).rowcount or 0
+                session.commit()
+
+            while True:
+                rows = session.execute(
+                    select(ImageRecord.id, ImageRecord.tagger_predictions)
+                    .where(ImageRecord.id > last_id)
+                    .where(ImageRecord.tagger_predictions.is_not(None))
+                    .order_by(ImageRecord.id.asc())
+                    .limit(500)
+                ).all()
+                if not rows:
+                    break
+                for image_id, preds in rows:
+                    scanned += 1
+                    if not preds:
+                        continue
+                    kept = {
+                        name: p for name, p in preds.items()
+                        if float(p.get("confidence", 0.0)) >= floor
+                    }
+                    if len(kept) != len(preds):
+                        session.execute(
+                            update(ImageRecord)
+                            .where(ImageRecord.id == image_id)
+                            .values(tagger_predictions=kept)
+                        )
+                        pruned += 1
+                session.commit()
+                last_id = rows[-1].id  # advance only after commit, for resume
+    except SoftTimeLimitExceeded:
+        log.warning(
+            "prune_low_confidence_predictions soft-limited at id=%s "
+            "(scanned=%d pruned=%d) — re-enqueuing", last_id, scanned, pruned,
+        )
+        prune_low_confidence_predictions_task.delay(last_id)
+        return {
+            "partial": True, "last_id": last_id,
+            "scanned": scanned, "pruned": pruned,
+        }
+
+    log.info(
+        "prune_low_confidence_predictions complete: floor=%s scanned=%d "
+        "pruned=%d allowlist_clamped=%d", floor, scanned, pruned, clamped,
+    )
+    return {
+        "floor": floor, "scanned": scanned, "pruned": pruned,
+        "allowlist_clamped": clamped, "last_id": last_id,
+    }
diff --git a/frontend/src/components/settings/MaintenancePanel.vue b/frontend/src/components/settings/MaintenancePanel.vue
index 76b85c5..69761d1 100644
--- a/frontend/src/components/settings/MaintenancePanel.vue
+++ b/frontend/src/components/settings/MaintenancePanel.vue
@@ -12,6 +12,7 @@
       <ThumbnailBackfillCard />
     </div>
     <MLThresholdSliders class="mt-4" />
+    <PrunePredictionsCard class="mt-4" />
     <AllowlistTable class="mt-4" />
     <AliasTable class="mt-4" />
     <DbMaintenanceCard class="mt-6" />
@@ -31,6 +32,7 @@ import MLBackfillCard from './MLBackfillCard.vue'
 import CentroidRecomputeCard from './CentroidRecomputeCard.vue'
 import ThumbnailBackfillCard from './ThumbnailBackfillCard.vue'
 import MLThresholdSliders from './MLThresholdSliders.vue'
+import PrunePredictionsCard from './PrunePredictionsCard.vue'
 import AllowlistTable from './AllowlistTable.vue'
 import AliasTable from './AliasTable.vue'
 import DbMaintenanceCard from './DbMaintenanceCard.vue'
diff --git a/frontend/src/components/settings/PrunePredictionsCard.vue b/frontend/src/components/settings/PrunePredictionsCard.vue
new file mode 100644
index 0000000..f3af5dc
--- /dev/null
+++ b/frontend/src/components/settings/PrunePredictionsCard.vue
@@ -0,0 +1,58 @@
+<template>
+  <!-- #764: drop stored tagger predictions below the store floor to shrink
+       image_record's TOAST (the sub-0.70 score tail had grown it to ~100 GB). -->
+  <v-card>
+    <v-card-title>Prune low-confidence predictions</v-card-title>
+    <v-card-text>
+      <p class="text-body-2 mb-3">
+        Removes stored tagger predictions below the current store floor
+        (<strong>{{ floorPct }}</strong>) from every image, and clamps any
+        allowlist threshold below the floor up to it. This is what shrinks the
+        database — the low-confidence tail was the bulk of its size. Idempotent
+        and resumable; safe to run more than once. Afterward, reclaim the freed
+        space with <code>VACUUM FULL</code> / <code>pg_repack</code> on
+        <code>image_record</code>.
+      </p>
+      <v-btn color="primary" rounded="pill" :loading="busy" @click="run">
+        <v-icon start>mdi-database-minus-outline</v-icon> Prune predictions now
+      </v-btn>
+      <span v-if="queued" class="ml-3 text-caption text-success">Queued ✓</span>
+      <QueueStatusBar queue="maintenance_long" queue-label="Maintenance (long)" />
+    </v-card-text>
+  </v-card>
+</template>
+
+<script setup>
+import { computed, onMounted, ref } from 'vue'
+
+import { useApi } from '../../composables/useApi.js'
+import { toast } from '../../utils/toast.js'
+import { useMLStore } from '../../stores/ml.js'
+import QueueStatusBar from './QueueStatusBar.vue'
+
+const api = useApi()
+const ml = useMLStore()
+const busy = ref(false)
+const queued = ref(false)
+
+const floorPct = computed(() => {
+  const f = ml.settings?.tagger_store_floor
+  return f == null ? '—' : `${Math.round(f * 100)}%`
+})
+
+onMounted(() => { if (!ml.settings) ml.loadSettings() })
+
+async function run () {
+  busy.value = true
+  queued.value = false
+  try {
+    await api.post('/api/admin/maintenance/prune-predictions')
+    queued.value = true
+    toast({ text: 'Prediction prune queued', type: 'success' })
+  } catch (e) {
+    toast({ text: e?.body?.detail || e?.message || 'Failed to queue', type: 'error' })
+  } finally {
+    busy.value = false
+  }
+}
+</script>
diff --git a/tests/test_tasks_admin.py b/tests/test_tasks_admin.py
index 948dd39..d975259 100644
--- a/tests/test_tasks_admin.py
+++ b/tests/test_tasks_admin.py
@@ -42,6 +42,68 @@ def test_bulk_delete_images_task_registered():
     )
 
 
+def test_prune_low_confidence_predictions_task_registered():
+    assert (
+        "backend.app.tasks.admin.prune_low_confidence_predictions_task"
+        in celery.tasks
+    )
+
+
+@pytest.mark.asyncio
+async def test_prune_low_confidence_predictions(db_sync, tmp_path):
+    # #764: drop stored tagger predictions below the store floor (default
+    # 0.70) and clamp allowlist thresholds up to it.
+    from backend.app.models import Tag, TagAllowlist, TagKind
+    from backend.app.tasks.admin import prune_low_confidence_predictions_task
+
+    f0 = tmp_path / "p0.jpg"
+    f0.write_bytes(b"x")
+    img0 = ImageRecord(
+        path=str(f0), sha256=f"{0:064x}", size_bytes=10, mime="image/jpeg",
+        origin="imported_filesystem",
+        tagger_predictions={
+            "keep_high": {"category": "general", "confidence": 0.92},
+            "keep_edge": {"category": "general", "confidence": 0.70},
+            "drop_mid": {"category": "general", "confidence": 0.40},
+            "drop_tiny": {"category": "general", "confidence": 0.06},
+        },
+    )
+    db_sync.add(img0)
+    f1 = tmp_path / "p1.jpg"
+    f1.write_bytes(b"x")
+    img1 = ImageRecord(
+        path=str(f1), sha256=f"{1:064x}", size_bytes=10, mime="image/jpeg",
+        origin="imported_filesystem",
+        tagger_predictions={"only": {"category": "general", "confidence": 0.99}},
+    )
+    db_sync.add(img1)
+    tag = Tag(name="lowthr-tag", kind=TagKind.general)
+    db_sync.add(tag)
+    db_sync.flush()
+    db_sync.add(TagAllowlist(tag_id=tag.id, min_confidence=0.30))
+    db_sync.commit()
+    img0_id, img1_id, tag_id = img0.id, img1.id, tag.id
+
+    result = prune_low_confidence_predictions_task.delay().get()
+    assert result["floor"] == pytest.approx(0.70)
+    assert result["pruned"] == 1            # only img0 had sub-floor entries
+    assert result["allowlist_clamped"] == 1
+
+    db_sync.expire_all()
+    p0 = db_sync.execute(
+        select(ImageRecord.tagger_predictions).where(ImageRecord.id == img0_id)
+    ).scalar_one()
+    assert set(p0) == {"keep_high", "keep_edge"}   # >=0.70 kept, <0.70 dropped
+    p1 = db_sync.execute(
+        select(ImageRecord.tagger_predictions).where(ImageRecord.id == img1_id)
+    ).scalar_one()
+    assert set(p1) == {"only"}                      # already clean — untouched
+    clamped = db_sync.execute(
+        select(TagAllowlist.min_confidence).where(TagAllowlist.tag_id == tag_id)
+    ).scalar_one()
+    assert clamped == pytest.approx(0.70)
+
+
 # --- delete_artist_cascade_task -------------------------------------