diff --git a/src/sentry/workflow_engine/endpoints/serializers/group_open_period_serializer.py b/src/sentry/workflow_engine/endpoints/serializers/group_open_period_serializer.py
index 01e835b06a0f5e..c9996888e67e8f 100644
--- a/src/sentry/workflow_engine/endpoints/serializers/group_open_period_serializer.py
+++ b/src/sentry/workflow_engine/endpoints/serializers/group_open_period_serializer.py
@@ -22,6 +22,7 @@ class GroupOpenPeriodResponse(TypedDict):
     start: datetime
     end: datetime | None
     isOpen: bool
+    eventId: str | None
     activities: list[GroupOpenPeriodActivityResponse] | None
 
 
@@ -89,5 +90,6 @@ def serialize(
                 else None
             ),
             isOpen=obj.date_ended is None,
+            eventId=obj.event_id,
             activities=attrs.get("activities"),
         )
diff --git a/tests/sentry/workflow_engine/endpoints/test_organization_open_periods.py b/tests/sentry/workflow_engine/endpoints/test_organization_open_periods.py
index 13571b0bf15430..388fe489c8242f 100644
--- a/tests/sentry/workflow_engine/endpoints/test_organization_open_periods.py
+++ b/tests/sentry/workflow_engine/endpoints/test_organization_open_periods.py
@@ -36,6 +36,8 @@ def setUp(self) -> None:
         DetectorGroup.objects.create(detector=self.detector, group=self.group)
 
         self.group_open_period = GroupOpenPeriod.objects.get(group=self.group)
+        self.group_open_period.event_id = "a" * 32
+        self.group_open_period.save()
 
         self.opened_gopa = GroupOpenPeriodActivity.objects.create(
             date_added=self.group_open_period.date_added,
@@ -66,6 +68,7 @@ def test_open_period_linked_to_group(self) -> None:
         assert open_period["start"] == self.group.first_seen
         assert open_period["end"] is None
         assert open_period["isOpen"] is True
+        assert open_period["eventId"] == self.group_open_period.event_id
         assert len(open_period["activities"]) == 1
         assert open_period["activities"][0] == {
             "id": str(self.opened_gopa.id),
@@ -114,6 +117,7 @@ def test_open_periods_resolved_group(self) -> None:
         assert resp["start"] == self.group.first_seen
         assert resp["end"] == resolved_time
         assert resp["isOpen"] is False
+        assert resp["eventId"] == open_period.event_id
         assert len(resp["activities"]) == 2
         assert resp["activities"][0] == {
             "id": str(self.opened_gopa.id),
@@ -199,6 +203,7 @@ def test_open_periods_unresolved_group(self) -> None:
         assert resp["start"] == unresolved_time
         assert resp["end"] == second_resolved_time
         assert resp["isOpen"] is False
+        assert resp["eventId"] == open_period2.event_id
         assert len(resp["activities"]) == 2
         assert resp["activities"][0] == {
             "id": str(opened_gopa2.id),
@@ -217,6 +222,7 @@ def test_open_periods_unresolved_group(self) -> None:
         assert resp2["start"] == self.group.first_seen
         assert resp2["end"] == resolved_time
         assert resp2["isOpen"] is False
+        assert resp2["eventId"] == open_period.event_id
         assert len(resp2["activities"]) == 2
         assert resp2["activities"][0] == {
             "id": str(self.opened_gopa.id),
@@ -290,6 +296,7 @@ def test_open_periods_limit(self) -> None:
         assert resp["start"] == unresolved_time
         assert resp["end"] == second_resolved_time
         assert resp["isOpen"] is False
+        assert resp["eventId"] == open_period.event_id
 
     def test_get_open_periods_time_range_starts_after_query_start(self) -> None:
         """Test that open periods starting after query_start and ending after query_end are included."""
@@ -448,6 +455,7 @@ def test_open_period_activities_time_period(self) -> None:
         assert open_period["start"] == self.group_open_period.date_started
         assert open_period["end"] is None
         assert open_period["isOpen"] is True
+        assert open_period["eventId"] == self.group_open_period.event_id
         assert (
             len(open_period["activities"]) == 1
         )  # don't include the opened GOPA, whose date_added doesn't overlap