diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_fired.ts
index f3d784d86d08a..96cb77e5f377c 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_fired.ts
@@ -54,7 +54,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -180,7 +179,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_no_data.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_no_data.ts
index 79d50d5bcf53f..9e0dbc4faa88f 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_no_data.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_pct_no_data.ts
@@ -40,7 +40,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       await createDataView({
@@ -148,7 +147,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_us_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_us_fired.ts
index 9adcba3a0acaa..702eda6da85d6 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_us_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/avg_us_fired.ts
@@ -48,7 +48,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       synthtraceEsClient = await getSyntraceClient({ esClient, kibanaUrl });
@@ -159,7 +158,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/custom_eq_avg_bytes_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/custom_eq_avg_bytes_fired.ts
index 5bacf710a9682..5262db27ca272 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/custom_eq_avg_bytes_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/custom_eq_avg_bytes_fired.ts
@@ -41,7 +41,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -177,7 +176,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/documents_count_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/documents_count_fired.ts
index dec612e4d7a92..e45683795d323 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/documents_count_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/documents_count_fired.ts
@@ -44,7 +44,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -177,7 +176,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/group_by_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/group_by_fired.ts
index 748439e7eec60..3074f34c23334 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/group_by_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/group_by_fired.ts
@@ -40,7 +40,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -177,7 +176,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/p99_pct_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/p99_pct_fired.ts
index 7e0fd56865c5e..22155b2b88719 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/p99_pct_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/p99_pct_fired.ts
@@ -54,7 +54,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -175,7 +174,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/rate_bytes_fired.ts b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/rate_bytes_fired.ts
index 41e0a664769d1..283d3fe1b2158 100644
--- a/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/rate_bytes_fired.ts
+++ b/x-pack/test/alerting_api_integration/observability/custom_threshold_rule/rate_bytes_fired.ts
@@ -40,7 +40,6 @@ export default function ({ getService }: FtrProviderContext) {
     let actionId: string;
     let ruleId: string;
     let alertId: string;
-    let startedAt: string;
 
     before(async () => {
       dataForgeConfig = {
@@ -173,7 +172,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',
diff --git a/x-pack/test_serverless/api_integration/test_suites/observability/custom_threshold_rule/group_by_fired.ts b/x-pack/test_serverless/api_integration/test_suites/observability/custom_threshold_rule/group_by_fired.ts
index f12fef06212b6..6638c7bef9d9d 100644
--- a/x-pack/test_serverless/api_integration/test_suites/observability/custom_threshold_rule/group_by_fired.ts
+++ b/x-pack/test_serverless/api_integration/test_suites/observability/custom_threshold_rule/group_by_fired.ts
@@ -30,7 +30,6 @@ export default function ({ getService }: FtrProviderContext) {
   const alertingApi = getService('alertingApi');
   const dataViewApi = getService('dataViewApi');
   let alertId: string;
-  let startedAt: string;
 
   describe('Custom Threshold rule - GROUP_BY - FIRED', () => {
     const CUSTOM_THRESHOLD_RULE_ALERT_INDEX = '.alerts-observability.threshold.alerts-default';
@@ -180,7 +179,6 @@ export default function ({ getService }: FtrProviderContext) {
           ruleId,
         });
         alertId = (resp.hits.hits[0]._source as any)['kibana.alert.uuid'];
-        startedAt = (resp.hits.hits[0]._source as any)['kibana.alert.start'];
 
         expect(resp.hits.hits[0]._source).property(
           'kibana.alert.rule.category',