diff --git a/examples/seller_agent.py b/examples/seller_agent.py
index a296becc7d..29b95497e4 100644
--- a/examples/seller_agent.py
+++ b/examples/seller_agent.py
@@ -702,21 +702,24 @@ def _package_budget_total(packages: list[dict[str, Any]]) -> Decimal:
 
 def _delivery_totals(events: list[dict[str, Any]]) -> dict[str, Any]:
     totals: dict[str, Any] = {
-        "impressions": sum(event.get("impressions", 0) for event in events),
         "spend": float(sum((Decimal(str(event.get("spend", 0))) for event in events), Decimal(0))),
     }
-    for metric in ("clicks", "conversions"):
+    # AdCP 3.3: an impression count nobody measured is absent, never zero.
+    for metric in ("impressions", "clicks", "conversions"):
         if any(metric in event for event in events):
             totals[metric] = sum(event.get(metric, 0) for event in events)
     views = [event["viewability"] for event in events if event.get("viewability")]
-    if views:
+    # AdCP 3.3: viewability reported under more than one standard has no flat
+    # total; one row is one (metric, qualifier) key.
+    if views and len({view.get("standard") for view in views}) == 1:
         measurable = sum(view.get("measurable_impressions", 0) for view in views)
         viewable = sum(view.get("viewable_impressions", 0) for view in views)
         totals["viewability"] = {
             "measurable_impressions": measurable,
             "viewable_impressions": viewable,
-            "viewable_rate": viewable / measurable if measurable else 0,
         }
+        if measurable:
+            totals["viewability"]["viewable_rate"] = viewable / measurable
         timed = [view for view in views if "viewed_seconds" in view]
         weight = sum(view.get("measurable_impressions", 0) for view in timed)
         if weight:
@@ -756,6 +759,20 @@ def _split_delivery(totals: dict[str, Any], weights: list[Decimal]) -> list[dict
     return results
 
 
+def _serves_impressionless_rows(context: Any) -> bool:
+    """Whether the caller's release (AdCP 3.3+) allows rows without ``impressions``.
+
+    Below 3.3 a dimensional row with no impression count is omitted, never
+    sent as ``impressions: 0``.
+    """
+    version = getattr(context, "resolved_adcp_version", None)
+    if not version:
+        return True
+    major, _, rest = str(version).partition(".")
+    minor = rest.split(".", 1)[0].split("-", 1)[0]
+    return not (major.isdigit() and minor.isdigit()) or (int(major), int(minor)) >= (3, 3)
+
+
 def _narrow_metrics(metrics: dict[str, Any], requested: list[str] | None) -> dict[str, Any]:
     if not requested:
         return metrics
@@ -1813,6 +1830,8 @@ async def get_media_buy_delivery(
                     "currency": mb.get("currency", "USD"),
                     **_narrow_metrics(metrics, requested),
                 }
+                if not _serves_impressionless_rows(context):
+                    rows = [row for row in rows if "impressions" in row]
                 if format_request is not None and reporting.get("supports_format_breakdown"):
                     sort_by = format_request.get("sort_by", "spend")
                     direction = format_request.get("sort_direction", "desc")
diff --git a/tests/test_seller_agent_storyboard.py b/tests/test_seller_agent_storyboard.py
index 8d07e217e8..377063fe7d 100644
--- a/tests/test_seller_agent_storyboard.py
+++ b/tests/test_seller_agent_storyboard.py
@@ -1234,3 +1234,57 @@ async def test_compact_catalog_ignores_outcome_target_and_paginates_fields() ->
     assert "products" not in unchanged
     invalid = await _seller().list_products({"cursor": "invalid"})
     assert invalid["errors"][0]["code"] == "INVALID_REQUEST"
+
+
+@pytest.mark.asyncio
+async def test_delivery_without_impressions_omits_them_and_rates() -> None:
+    """AdCP 3.3: absence means not measured; never fill zero or derive a rate."""
+    store = _store()
+    await store.seed_media_buy(
+        media_buy_id="unmeasured", fixture={"packages": [{"package_id": "p", "budget": 10}]}
+    )
+    cumulative = await store.simulate_delivery(
+        "unmeasured",
+        reported_spend={"amount": 5, "currency": "USD"},
+        viewability={"measurable_impressions": 0, "viewable_impressions": 0, "standard": "mrc"},
+    )
+    assert "impressions" not in cumulative["cumulative"]
+    report = await _seller().get_media_buy_delivery({"media_buy_ids": ["unmeasured"]})
+    buy = report["media_buy_deliveries"][0]
+    assert "impressions" not in buy["totals"]
+    assert "impressions" not in buy["by_package"][0]
+    assert "viewable_rate" not in buy["totals"]["viewability"]
+
+
+@pytest.mark.asyncio
+async def test_viewability_under_two_standards_has_no_flat_total() -> None:
+    """AdCP 3.3: a metric reported under more than one qualifier omits its flat carrier."""
+    store = _store()
+    await store.seed_media_buy(
+        media_buy_id="mixed-standards", fixture={"packages": [{"package_id": "p", "budget": 10}]}
+    )
+    for standard in ("mrc", "groupm"):
+        await store.simulate_delivery(
+            "mixed-standards",
+            impressions=100,
+            reported_spend={"amount": 1, "currency": "USD"},
+            viewability={
+                "measurable_impressions": 100,
+                "viewable_impressions": 50,
+                "standard": standard,
+            },
+        )
+    report = await _seller().get_media_buy_delivery({"media_buy_ids": ["mixed-standards"]})
+    totals = report["media_buy_deliveries"][0]["totals"]
+    assert totals["impressions"] == 200
+    assert "viewability" not in totals
+
+
+@pytest.mark.parametrize(
+    ("version", "expect_rows"), [("3.3-beta.1", True), ("3.2", False), (None, True)]
+)
+def test_impressionless_rows_are_served_only_from_33(version, expect_rows) -> None:
+    from types import SimpleNamespace
+
+    context = None if version is None else SimpleNamespace(resolved_adcp_version=version)
+    assert _sa._serves_impressionless_rows(context) is expect_rows