diff --git a/src/ingestion/dbt/tests/collaboration/assert_collab_document_counts_no_spike.sql b/src/ingestion/dbt/tests/collaboration/assert_collab_document_counts_no_spike.sql
new file mode 100644
index 000000000..ca89845b9
--- /dev/null
+++ b/src/ingestion/dbt/tests/collaboration/assert_collab_document_counts_no_spike.sql
@@ -0,0 +1,124 @@
+{{ config(
+    tags=['data_quality'],
+    severity='warn',
+    store_failures=true,
+    meta={
+        'title': 'Collab document activity spike vs per-user trailing baseline',
+        'domain': 'collab',
+        'category': 'anomaly',
+        'tier': 'warn',
+        'remediation': 'A recent user-day activity count is far above the recent history for that same user, product and metric (z-score > 5 AND > 10x the trailing mean over the last 28 observed days, with at least 14 days of history and a baseline that is itself recent). Not necessarily wrong — it can be a genuine burst — but a sudden 100x-style jump usually means a feeder double-count, a unit change, or a backfill landing on one date. Inspect the stored rows, compare value against base_mean, and trace the m365 feeder. Thresholds are heuristic and advisory (warn only); tune them once observed against real tenant data.'
+    }
+) }}
+-- Statistical spike guard for collaboration document activity (#1321 follow-up).
+-- Catches "too high" anomalies the non-negative check cannot: a count that is
+-- plausible in isolation but wildly out of line with the same user's own recent
+-- history. Deliberately NOT a fixed upper limit — the baseline is derived per
+-- (tenant, user, product, metric) from each series' own trailing window, so it
+-- adapts to heavy and light users alike instead of one global number.
+--
+-- Bounded by design, so the cost stays flat as history grows:
+--   * input is capped to the last 120 days (the `recent` CTE). A 28-observed-day
+--     baseline for any reasonably active user fits well inside 120 calendar days,
+--     so the window sort/scan never grows with total history. A user with fewer
+--     than 14 active days in that window simply isn't evaluated (too little
+--     signal), which the prior_n guard below enforces.
+--   * output is capped to rows collected in the last 3 days (collected_at, the
+--     row arrival time -- not activity date), so a scheduled daily run reports
+--     newly-arrived spikes once, and a late backfill landing today for an older
+--     activity date is still caught instead of being silently dropped.
+--
+-- Method: unpivot the five activity counts, then for each series compute a
+-- trailing baseline over the previous 28 observed days (excluding the current
+-- day). A day is flagged only when ALL of these hold:
+--   * at least 14 prior observations exist   -- cold-start guard, no baseline yet
+--   * the baseline has non-zero spread        -- avoids divide-by-noise on flat series
+--   * the most recent prior observation is within 35 days  -- baseline is not stale
+--   * value > mean + 5 * stddev               -- z-score outlier
+--   * value > 10 * mean                        -- massive relative jump
+-- The window is ROWS-based (observed days, not calendar days), so without the
+-- staleness guard a user returning from a long leave would be compared against a
+-- months-old baseline and could false-fire; `date - prev_date <= 35` prevents
+-- that. Advisory only (severity=warn): it emits a finding and stores the rows, it
+-- never fails the pipeline. Read FINAL so transient ReplacingMergeTree duplicates
+-- can't look like spikes.
+WITH recent AS (
+    SELECT
+        tenant_id,
+        insight_source_id,
+        person_key,
+        product,
+        data_source,
+        date,
+        collected_at,
+        viewed_or_edited_count,
+        synced_count,
+        shared_internally_count,
+        shared_externally_count,
+        visited_page_count
+    FROM {{ ref('class_collab_document_activity') }} FINAL
+    WHERE date >= today() - 120
+),
+unpivoted AS (
+    SELECT
+        tenant_id,
+        insight_source_id,
+        person_key,
+        product,
+        data_source,
+        date,
+        collected_at,
+        m.1 AS metric,
+        m.2 AS value
+    FROM recent
+    ARRAY JOIN
+        [
+            ('viewed_or_edited_count',  CAST(viewed_or_edited_count  AS Nullable(Float64))),
+            ('synced_count',            CAST(synced_count            AS Nullable(Float64))),
+            ('shared_internally_count', CAST(shared_internally_count AS Nullable(Float64))),
+            ('shared_externally_count', CAST(shared_externally_count AS Nullable(Float64))),
+            ('visited_page_count',      CAST(visited_page_count      AS Nullable(Float64)))
+        ] AS m
+    WHERE m.2 IS NOT NULL
+),
+baselined AS (
+    SELECT
+        tenant_id,
+        insight_source_id,
+        person_key,
+        product,
+        data_source,
+        date,
+        collected_at,
+        metric,
+        value,
+        count()           OVER w AS prior_n,
+        avg(value)        OVER w AS base_mean,
+        stddevSamp(value) OVER w AS base_sd,
+        max(date)         OVER w AS prev_date
+    FROM unpivoted
+    WINDOW w AS (
+        PARTITION BY tenant_id, insight_source_id, person_key, product, data_source, metric
+        ORDER BY date
+        ROWS BETWEEN 28 PRECEDING AND 1 PRECEDING
+    )
+)
+SELECT
+    tenant_id,
+    insight_source_id,
+    person_key,
+    product,
+    data_source,
+    date,
+    metric,
+    value,
+    prior_n,
+    base_mean,
+    base_sd
+FROM baselined
+WHERE prior_n >= 14
+  AND base_sd > 0
+  AND (date - prev_date) <= 35
+  AND value > base_mean + 5 * base_sd
+  AND value > base_mean * 10
+  AND collected_at >= today() - 3