diff --git a/.github/scripts/tests/therock_nightly_test_scope_test.py b/.github/scripts/tests/therock_nightly_test_scope_test.py
new file mode 100644
index 000000000000..ec317857491a
--- /dev/null
+++ b/.github/scripts/tests/therock_nightly_test_scope_test.py
@@ -0,0 +1,59 @@
+import json
+import os
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+from typing import List
+
+sys.path.insert(0, os.fspath(Path(__file__).parent.parent))
+import therock_nightly_test_scope as scope
+
+
+def write_config(tmpdir: str, names: List[tuple]) -> Path:
+    entries = [
+        {
+            "name": name,
+            "url": f"ROCm/{name}",
+            "branch": "develop",
+            "category": category,
+            "auto_subtree_pull": False,
+            "auto_subtree_push": True,
+            "monorepo_source_of_truth": True,
+        }
+        for category, name in names
+    ]
+    config_path = Path(tmpdir) / "repos-config.json"
+    config_path.write_text(json.dumps({"repositories": entries}), encoding="utf-8")
+    return config_path
+
+
+class NightlyTestScopeTest(unittest.TestCase):
+    def test_returns_sorted_category_name_pairs(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            config_path = write_config(
+                tmpdir,
+                [
+                    ("projects", "rocsparse"),
+                    ("shared", "hipblas-common"),
+                    ("projects", "rocblas"),
+                ],
+            )
+            self.assertEqual(
+                scope.get_test_projects(config_path),
+                ["projects/rocblas", "projects/rocsparse", "shared/hipblas-common"],
+            )
+
+    def test_empty_config_fails_instead_of_testing_everything(self):
+        # An empty changed_projects means "test everything" to TheRock.
+        with tempfile.TemporaryDirectory() as tmpdir:
+            config_path = write_config(tmpdir, [])
+            with self.assertRaises(SystemExit):
+                scope.main(["--config", os.fspath(config_path)])
+
+    def test_real_config_is_non_empty(self):
+        self.assertTrue(scope.get_test_projects(scope.DEFAULT_CONFIG_PATH))
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/.github/scripts/therock_nightly_test_scope.py b/.github/scripts/therock_nightly_test_scope.py
new file mode 100644
index 000000000000..6cd5471307e3
--- /dev/null
+++ b/.github/scripts/therock_nightly_test_scope.py
@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+
+"""Emits the subtrees the multi-arch nightly CI should test, as `category/name`.
+
+TEMPORARY: a scheduled run has no diff to narrow testing against, so TheRock
+tests every component it builds, including ROCm system components (hip-tests,
+rocrtst, rocgdb, amdsmi, ...) that no change here can affect. Passing every
+subtree in repos-config.json as `changed_projects` scopes it back to the code
+this repo owns. Delete this script, its test, and the `configure` job in
+therock-multi-arch-ci-nightly.yml once TheRock scopes schedule runs natively.
+"""
+
+import argparse
+import logging
+from pathlib import Path
+from typing import List, Optional
+
+from ci_utils import append_step_summary, set_github_output
+from config_loader import load_repo_config
+from pr_detect_changed_subtrees import get_valid_prefixes
+
+DEFAULT_CONFIG_PATH = Path(__file__).resolve().parent.parent / "repos-config.json"
+
+
+def get_test_projects(config_path: Path) -> List[str]:
+    """Return every subtree in repos-config.json as a sorted `category/name` list."""
+    return sorted(get_valid_prefixes(load_repo_config(str(config_path))))
+
+
+def format_step_summary(test_projects: List[str]) -> str:
+    """Render the test scope as a markdown step summary."""
+    subtrees = "\n".join(test_projects)
+    return (
+        "### Nightly test scope\n\n"
+        "Testing rocm-libraries subtrees and their direct consumers only:\n\n"
+        f"```\n{subtrees}\n```\n"
+    )
+
+
+def main(argv: Optional[List[str]] = None) -> None:
+    logging.basicConfig(level=logging.INFO)
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--config",
+        type=Path,
+        default=DEFAULT_CONFIG_PATH,
+        help="Path to the repos-config.json file",
+    )
+    args = parser.parse_args(argv)
+
+    test_projects = get_test_projects(args.config)
+    if not test_projects:
+        # TheRock reads an empty `changed_projects` as "test everything".
+        raise SystemExit(f"No subtrees found in {args.config}")
+
+    set_github_output({"test_projects": ",".join(test_projects)})
+    append_step_summary(format_step_summary(test_projects))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/.github/workflows/therock-multi-arch-ci-nightly.yml b/.github/workflows/therock-multi-arch-ci-nightly.yml
index b32752dbf10d..9d68a6d74e47 100644
--- a/.github/workflows/therock-multi-arch-ci-nightly.yml
+++ b/.github/workflows/therock-multi-arch-ci-nightly.yml
@@ -9,6 +9,12 @@
 # test hardware exists for that family yet (see amdgpu_family_matrix.py in
 # TheRock, family key "gfx125x": test-runs-on is empty everywhere).
 #
+# Testing is scoped to the subtrees listed in .github/repos-config.json rather
+# than to all of ROCm. A schedule run has no diff to narrow against, so TheRock
+# would otherwise test every component it builds, including system components
+# (hip-tests, rocrtst, rocgdb, rocprofiler-*, amdsmi, rccl, ...) that this
+# repository cannot affect.
+#
 # For manual triggering with custom GPU families, use therock-multi-arch-ci.yml.
 
 name: TheRock Multi-Arch Nightly CI
@@ -33,6 +39,30 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  configure:
+    name: Configure Test Scope
+    runs-on: ubuntu-26.04
+    outputs:
+      test_projects: ${{ steps.scope.outputs.test_projects }}
+    steps:
+      - name: Checkout CI config
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          sparse-checkout: .github
+          sparse-checkout-cone-mode: true
+
+      - name: Set up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: "3.12"
+
+      - name: Install python dependencies
+        run: pip install pydantic requests
+
+      - name: Collect rocm-libraries subtrees
+        id: scope
+        run: python .github/scripts/therock_nightly_test_scope.py
+
   setup:
     uses: ROCm/TheRock/.github/workflows/setup_multi_arch.yml@47434387de730d51788b705e5600602dd6064997 # 2026-10-16
     with:
@@ -85,7 +115,7 @@ jobs:
 
   linux_build_and_test:
     name: Linux::${{ fromJSON(needs.setup.outputs.linux_build_config || '{}').build_variant_label || 'skip' }}
-    needs: [setup]
+    needs: [configure, setup]
     if: >-
       ${{
         needs.setup.outputs.linux_build_config != '' &&
@@ -101,8 +131,12 @@ jobs:
       rocm_rpm_package_version: ${{ needs.setup.outputs.rocm_rpm_package_version }}
       test_type: ${{ needs.setup.outputs.test_type }}
       external_repo_config: ${{ needs.setup.outputs.external_repo_config }}
-      # Empty string triggers full test run in downstream workflow
-      changed_projects: ''
+      # Scope testing to the subtrees this repository owns (plus the consumers
+      # TheRock's dependency graph pulls in). An empty string would mean "test
+      # everything", which on a schedule run spends GPU runner time on ROCm
+      # system components (hip-tests, rocrtst, rocgdb, rocprofiler-*, amdsmi,
+      # ...) that no rocm-libraries change can affect.
+      changed_projects: ${{ needs.configure.outputs.test_projects }}
       repository: ROCm/TheRock
       ref: 47434387de730d51788b705e5600602dd6064997 # 2026-10-16
     permissions:
@@ -111,7 +145,7 @@ jobs:
 
   windows_build_and_test:
     name: Windows::${{ fromJSON(needs.setup.outputs.windows_build_config || '{}').build_variant_label || 'skip' }}
-    needs: [setup]
+    needs: [configure, setup]
     if: >-
       ${{
         needs.setup.outputs.windows_build_config != '' &&
@@ -125,8 +159,8 @@ jobs:
       rocm_package_version: ${{ needs.setup.outputs.rocm_package_version }}
       test_type: ${{ needs.setup.outputs.test_type }}
       external_repo_config: ${{ needs.setup.outputs.external_repo_config }}
-      # Empty string triggers full test run in downstream workflow
-      changed_projects: ''
+      # See the Linux job above: scope testing to rocm-libraries-owned subtrees.
+      changed_projects: ${{ needs.configure.outputs.test_projects }}
       repository: ROCm/TheRock
       ref: 47434387de730d51788b705e5600602dd6064997 # 2026-10-16
     permissions:
@@ -137,6 +171,7 @@ jobs:
     name: Multi-Arch CI Summary
     if: always()
     needs:
+      - configure
       - setup
       - linux_build_and_test
       - windows_build_and_test