diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 91c5975fc8..4a9c7f9910 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -112,6 +112,10 @@ This repository contains three interconnected applications:
 
 - Pay attention to available types and type guards in src/SIL.XForge.Scripture/ClientApp/src/type-utils.ts.
 
+# Tests
+
+- Place a line with "// SUT" before the line that causes the code being tested to be exercised.
+
 # Running commands
 
 - If you run frontend tests, run them in the `src/SIL.XForge.Scripture/ClientApp` directory with a command such as `npm run test:headless -- --watch=false --include '**/text.component.spec.ts' --include '**/settings.component.spec.ts'`
diff --git a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.html b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.html
index df01a2d9d7..7a60def055 100644
--- a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.html
+++ b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.html
@@ -48,6 +48,13 @@
     </div>
   </div>
 
+  @if (shouldShowDurationComparisonCaution) {
+    <app-notice icon="calendar_month" type="warning">
+      Be careful about comparing Serval build outcomes and durations before 2025-12-18 with those after, because of
+      changes to the event grouping system.
+    </app-notice>
+  }
+
   @if (!isLoading) {
     @if (currentProjectFilter) {
       <app-notice icon="filter_alt" mode="fill-dark">
diff --git a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.spec.ts b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.spec.ts
index 3144953edf..8a9960edb9 100644
--- a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.spec.ts
+++ b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.spec.ts
@@ -650,6 +650,35 @@ describe('DraftJobsComponent', () => {
       }));
     });
 
+    describe('shouldShowDurationComparisonCaution', () => {
+      it('should return false if no date range is set', fakeAsync(() => {
+        const env = new TestEnvironment({ hasEvents: false });
+        env.wait();
+        env.component['currentDateRange'] = undefined;
+
+        // SUT
+        expect(env.component.shouldShowDurationComparisonCaution).toBeFalse();
+      }));
+
+      it('should return true when the date range starts before the cutoff', fakeAsync(() => {
+        const env = new TestEnvironment({ hasEvents: false });
+        env.wait();
+        env.setDateRange(new Date(2025, 12 - 1, 1), new Date(2026, 1 - 1, 20));
+
+        // SUT
+        expect(env.component.shouldShowDurationComparisonCaution).toBeTrue();
+      }));
+
+      it('should return false when the date range starts on or after the cutoff', fakeAsync(() => {
+        const env = new TestEnvironment({ hasEvents: false });
+        env.wait();
+        env.setDateRange(new Date(2026, 1 - 1, 20), new Date(2026, 2 - 1, 20));
+
+        // SUT
+        expect(env.component.shouldShowDurationComparisonCaution).toBeFalse();
+      }));
+    });
+
     describe('formatDurationInHours', () => {
       it('should format duration in decimal hours', fakeAsync(() => {
         const env = new TestEnvironment({ hasEvents: false });
diff --git a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.ts b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.ts
index 05a6bfc256..5a95b5f581 100644
--- a/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.ts
+++ b/src/SIL.XForge.Scripture/ClientApp/src/app/serval-administration/draft-jobs.component.ts
@@ -210,6 +210,19 @@ export class DraftJobsComponent extends DataLoadingComponent implements OnInit {
     return this.formatDurationInHours(this.maxDuration);
   }
 
+  /** Whether to show a caution notice about comparing older durations. */
+  get shouldShowDurationComparisonCaution(): boolean {
+    if (this.currentDateRange == null) return false;
+
+    // Day after the date when draftGenerationRequestId began to be used, which was in SFv5.46.1 at
+    // 2025-12-18T17:48:57Z.
+    const requestIdIntroductionDate: Date = new Date(2025, 12 - 1, 18 + 1);
+
+    const rangeStartMs: number = this.currentDateRange.start.getTime();
+    const cutoffMs: number = requestIdIntroductionDate.getTime();
+    return rangeStartMs < cutoffMs;
+  }
+
   ngOnInit(): void {
     if (
       !this.columnsToDisplay.includes('buildDetails') &&