diff --git a/aws/lambda/cross_repo_ci_relay/callback/callback_handler.py b/aws/lambda/cross_repo_ci_relay/callback/callback_handler.py
index 7d76a7395c..f7ad107ed8 100644
--- a/aws/lambda/cross_repo_ci_relay/callback/callback_handler.py
+++ b/aws/lambda/cross_repo_ci_relay/callback/callback_handler.py
@@ -203,6 +203,7 @@ def _create_upstream_check_run(
     workflow_name: str,
     job_name: str | None,
     details_url: str,
+    pr_number: str = "",
 ) -> None:
     """Create a new upstream check run mirroring the downstream job's status.
 
@@ -233,7 +234,7 @@ def _create_upstream_check_run(
             details_url=details_url,
             # Store the downstream run_id so a check-run rerequest can re-run
             # the failed jobs of that workflow run.
-            external_id=str(run_id),
+            external_id=f"{run_id}:{pr_number}" if pr_number else str(run_id),
             output=output,
         )
         logger.info(
@@ -369,6 +370,7 @@ def handle(config: RelayConfig, body: dict, verified_repo: str) -> dict:
     if repo_level.value >= AllowlistLevel.L3.value:
         pr_field = (body.get("payload") or {}).get("pull_request") or {}
         head_sha = (pr_field.get("head") or {}).get("sha", "")
+        pr_number = str(pr_field.get("number") or "")
         if head_sha:
             conclusion = (body.get("workflow") or {}).get("conclusion")
             details_url = f"https://github.com/{verified_repo}/actions/runs/{run_id}"
@@ -408,6 +410,7 @@ def handle(config: RelayConfig, body: dict, verified_repo: str) -> dict:
                     workflow_name=workflow_name,
                     job_name=job_name,
                     details_url=details_url,
+                    pr_number=pr_number,
                 )
 
     if status == "in_progress":
diff --git a/aws/lambda/cross_repo_ci_relay/callback/cleanup_handler.py b/aws/lambda/cross_repo_ci_relay/callback/cleanup_handler.py
index e5f2b55c2a..972f6ac9d0 100644
--- a/aws/lambda/cross_repo_ci_relay/callback/cleanup_handler.py
+++ b/aws/lambda/cross_repo_ci_relay/callback/cleanup_handler.py
@@ -83,6 +83,7 @@ def _finalize_timed_out_check_run(
 
     pr_field = (body.get("payload") or {}).get("pull_request") or {}
     head_sha = (pr_field.get("head") or {}).get("sha", "")
+    pr_number = str(pr_field.get("number") or "")
     if not head_sha:
         return
 
@@ -117,7 +118,7 @@ def _finalize_timed_out_check_run(
             status="completed",
             conclusion="timed_out",
             details_url=details_url,
-            external_id=run_id,
+            external_id=f"{run_id}:{pr_number}" if pr_number else run_id,
             output=output,
         )
         logger.info(
diff --git a/aws/lambda/cross_repo_ci_relay/tests/test_callback_handler.py b/aws/lambda/cross_repo_ci_relay/tests/test_callback_handler.py
index f6193a813f..c0f7033d8b 100644
--- a/aws/lambda/cross_repo_ci_relay/tests/test_callback_handler.py
+++ b/aws/lambda/cross_repo_ci_relay/tests/test_callback_handler.py
@@ -365,7 +365,7 @@ def test_check_run_external_id_is_run_id(self):
         )
 
         kw = self.mock_gh.create_check_run.call_args[1]
-        self.assertEqual(kw["external_id"], "99999")  # run_id from _body
+        self.assertEqual(kw["external_id"], "99999:42")  # run_id:pr_number
 
     def test_in_progress_callback_creates_check_run(self):
         self.mock_gh.create_check_run.return_value = 999
diff --git a/aws/lambda/cross_repo_ci_relay/tests/test_event_handler.py b/aws/lambda/cross_repo_ci_relay/tests/test_event_handler.py
index e663c364bb..44df54ce6a 100644
--- a/aws/lambda/cross_repo_ci_relay/tests/test_event_handler.py
+++ b/aws/lambda/cross_repo_ci_relay/tests/test_event_handler.py
@@ -191,7 +191,7 @@ def test_scenario2_in_progress_job_creates_in_progress_check_run(self):
         self.assertEqual(kw["head_sha"], "abc123")
         self.assertEqual(kw["status"], "in_progress")
         self.assertIsNone(kw["conclusion"])
-        self.assertEqual(kw["external_id"], "99999")  # run_id
+        self.assertEqual(kw["external_id"], "99999:42")  # run_id:pr_number
 
     def test_scenario2_backfills_every_job_not_just_one(self):
         """Multi-job workflow: a mid-run label backfills a check run for EVERY
@@ -215,7 +215,7 @@ def test_scenario2_backfills_every_job_not_just_one(self):
             c.kwargs["external_id"]
             for c in self.mock_gh.create_check_run.call_args_list
         }
-        self.assertEqual(external_ids, {"99999"})  # run_id
+        self.assertEqual(external_ids, {"99999:42"})  # run_id:pr_number
 
     def test_scenario3_completed_job_creates_completed_check_run(self):
         """Scenario 3: label arrives after workflow completed → create completed CR directly."""
diff --git a/aws/lambda/cross_repo_ci_relay/webhook/event_handler.py b/aws/lambda/cross_repo_ci_relay/webhook/event_handler.py
index 2573aa2a27..59157c6c9c 100644
--- a/aws/lambda/cross_repo_ci_relay/webhook/event_handler.py
+++ b/aws/lambda/cross_repo_ci_relay/webhook/event_handler.py
@@ -152,7 +152,7 @@ def _handle_pr_labeled(config: RelayConfig, payload: dict) -> dict:
         return {"ok": True, "created_check_runs": []}
 
     pr = payload.get("pull_request") or {}
-    pr_number = str(pr.get("number", ""))
+    pr_number = str(pr.get("number") or "")
     head_sha = (pr.get("head") or {}).get("sha", "")
     if not pr_number or not head_sha:
         return {"ignored": True, "reason": "missing pr context"}
@@ -205,9 +205,12 @@ def _handle_pr_labeled(config: RelayConfig, payload: dict) -> dict:
                     status=job_status,
                     conclusion=(job_conclusion if job_status == "completed" else None),
                     details_url=details_url,
-                    external_id=str(run_id),
+                    external_id=f"{run_id}:{pr_number}" if pr_number else str(run_id),
                     output=gh_helper.build_check_run_output(
-                        job_status, job_conclusion, details_url, downstream_repo
+                        job_status,
+                        job_conclusion,
+                        details_url,
+                        downstream_repo,
                     ),
                 )
                 created.append(f"{downstream_repo}/{job_name}")
@@ -263,7 +266,7 @@ def _handle_check_run_rerequested(config: RelayConfig, payload: dict) -> dict:
     """
     check_run = payload.get("check_run") or {}
     name = check_run.get("name", "")
-    run_id = check_run.get("external_id") or ""
+    run_id = (check_run.get("external_id") or "").split(":")[0]
     downstream_repo = _downstream_repo_from_check_run(name)
     if not downstream_repo or not run_id:
         return {"ignored": True, "reason": "not a crcr check run"}
@@ -346,7 +349,7 @@ def _handle_check_suite_rerequested(config: RelayConfig, payload: dict) -> dict:
     rerun: list[str] = []
     for check_run in check_runs:
         downstream_repo = _downstream_repo_from_check_run(check_run.get("name", ""))
-        run_id = check_run.get("external_id") or ""
+        run_id = (check_run.get("external_id") or "").split(":")[0]
         if not downstream_repo or not run_id:
             continue
         if (downstream_repo, run_id) in seen:
diff --git a/torchci/lib/bot/crcrOncallBot.ts b/torchci/lib/bot/crcrOncallBot.ts
index c77782ec95..0375489d14 100644
--- a/torchci/lib/bot/crcrOncallBot.ts
+++ b/torchci/lib/bot/crcrOncallBot.ts
@@ -80,27 +80,13 @@ export default function crcrOncallBot(app: Probot): void {
     }
 
     // Get the PRs this check run belongs to.
-    // checkRun.pull_requests is empty for cross-fork PRs (most pytorch
-    // contributions), so fall back to the commits API to resolve PRs
-    // from the head SHA — the same strategy used by the merge-blocking path.
     let prNumbers: number[] = [];
     if (checkRun.pull_requests && checkRun.pull_requests.length > 0) {
       prNumbers = checkRun.pull_requests.map((pr) => pr.number);
-    } else if (checkRun.head_sha) {
-      try {
-        const result =
-          await ctx.octokit.rest.repos.listPullRequestsAssociatedWithCommit({
-            owner,
-            repo,
-            commit_sha: checkRun.head_sha,
-          });
-        prNumbers = result.data.map((pr: any) => pr.number);
-      } catch (err) {
-        ctx.log(
-          { err },
-          `crcrOncall: failed to resolve PRs for commit ${checkRun.head_sha}, skipping`
-        );
-        return;
+    } else if (checkRun.external_id) {
+      const parts = checkRun.external_id.split(":");
+      if (parts.length === 2 && parts[1]) {
+        prNumbers = [parseInt(parts[1], 10)];
       }
     }
 
diff --git a/torchci/test/crcrOncallBot.test.ts b/torchci/test/crcrOncallBot.test.ts
index 368241557c..fa54d5fb28 100644
--- a/torchci/test/crcrOncallBot.test.ts
+++ b/torchci/test/crcrOncallBot.test.ts
@@ -176,16 +176,46 @@ L3:
     });
   });
 
-  test("does not comment when no PR is associated", async () => {
+  test("does not comment when external_id has no PR number", async () => {
+    // external_id carries bare run_id (no ":" separator) when pr_number
+    // is unavailable — the bot returns early without any API call.
     await probot.receive({
       name: "check_run" as any,
       payload: checkRunPayload({
         pull_requests: [],
+        external_id: "12345",
       }) as any,
       id: "8",
     });
   });
 
+  test("posts comment when external_id contains PR number for cross-fork PR", async () => {
+    const scope = nock("https://api.github.com")
+      .get(`/repos/${OWNER}/${REPO}/issues/${PR_NUMBER}/comments`)
+      .reply(200, [])
+      .post(
+        `/repos/${OWNER}/${REPO}/issues/${PR_NUMBER}/comments`,
+        (body: any) => {
+          expect(body.body).toContain(
+            "<!-- crcr-oncall:intel/torch-xpu-ops -->"
+          );
+          expect(body.body).toContain("@oncall_xpu");
+          return true;
+        }
+      )
+      .reply(200);
+
+    await probot.receive({
+      name: "check_run" as any,
+      payload: checkRunPayload({
+        pull_requests: [], // empty — simulates cross-fork PR
+        external_id: `12345:${PR_NUMBER}`,
+      }) as any,
+      id: "10",
+    });
+    handleScope(scope);
+  });
+
   test("does nothing for unsupported org", async () => {
     const payload = checkRunPayload();
     payload.repository = {