diff --git a/.buildkite/pipeline-utils/affected-packages/README.md b/.buildkite/pipeline-utils/affected-packages/README.md
index 0255754e54e1e..af12c794967e4 100644
--- a/.buildkite/pipeline-utils/affected-packages/README.md
+++ b/.buildkite/pipeline-utils/affected-packages/README.md
@@ -129,3 +129,7 @@ const filteredFiles = filterFilesByPackages(
 2. Return affected project IDs
 
 **Performance**: ~5-7 seconds
+
+## PR Jest selective testing
+
+On pull request builds, Jest unit and integration test groups are narrowed to configs under affected packages (see `pick_test_group_run_order` in CI stats). Add the GitHub label `ci:prevent-selective-testing` to run the full Jest suite instead. Touching files listed in `CRITICAL_FILES_JEST_*` in `const.ts` also skips filtering for the relevant test type.
diff --git a/.buildkite/pipeline-utils/affected-packages/const.ts b/.buildkite/pipeline-utils/affected-packages/const.ts
index 5d2b34599978f..0f10919ea6190 100644
--- a/.buildkite/pipeline-utils/affected-packages/const.ts
+++ b/.buildkite/pipeline-utils/affected-packages/const.ts
@@ -9,7 +9,7 @@
 
 export const UNCATEGORIZED_MODULE_ID = '[uncategorized]';
 
-export const SELECTIVE_TESTS_LABEL = 'ci:use-selective-testing';
+export const PREVENT_SELECTIVE_TESTS_LABEL = 'ci:prevent-selective-testing';
 
 // Changes here skip affected-package filtering for Jest (full run).
 // Keep narrow: global test harness, transforms, CI selection.
diff --git a/.buildkite/pipeline-utils/ci-stats/pick_test_group_run_order.ts b/.buildkite/pipeline-utils/ci-stats/pick_test_group_run_order.ts
index 14136733ca3c5..3132680608609 100644
--- a/.buildkite/pipeline-utils/ci-stats/pick_test_group_run_order.ts
+++ b/.buildkite/pipeline-utils/ci-stats/pick_test_group_run_order.ts
@@ -25,15 +25,20 @@ import {
   getAffectedPackages,
   listChangedFiles,
   filterFilesByPackages,
-  SELECTIVE_TESTS_LABEL,
+  PREVENT_SELECTIVE_TESTS_LABEL,
   CRITICAL_FILES_JEST_UNIT_TESTS,
   touchedCriticalFiles,
   CRITICAL_FILES_JEST_INTEGRATION_TESTS,
 } from '../affected-packages';
 import { collectEnvFromLabels, expandAgentQueue, getRequiredEnv } from '#pipeline-utils';
 
-// TODO: this is always false on on-merge, when switching to enable this by default, check if this is a PR
-const USE_SELECTIVE_TESTING = process.env.GITHUB_PR_LABELS?.includes(SELECTIVE_TESTS_LABEL);
+const prLabels =
+  process.env.GITHUB_PR_LABELS?.split(',')
+    .map((l) => l.trim())
+    .filter(Boolean) ?? [];
+const isPrBuild = Boolean(process.env.GITHUB_PR_NUMBER);
+const preventSelectiveTesting = prLabels.includes(PREVENT_SELECTIVE_TESTS_LABEL);
+const USE_SELECTIVE_TESTING = isPrBuild && !preventSelectiveTesting;
 
 const ALL_FTR_MANIFEST_REL_PATHS = serverless.concat(stateful);