diff --git a/.github/workflows/_pr-test-stage.yml b/.github/workflows/_pr-test-stage.yml
index 42c22191acb2..4b9176307841 100644
--- a/.github/workflows/_pr-test-stage.yml
+++ b/.github/workflows/_pr-test-stage.yml
@@ -107,8 +107,11 @@ jobs:
     # caller that declares its runners as a matrix cannot, since job-level `if`
     # sees github/needs/vars/inputs but not `matrix`. Callers that never declare
     # the input read back null and match every runner_config.
+    # Temporarily skip the unavailable GB300 runner before GitHub tries to
+    # allocate it. Covers both callers: pr-test and nightly.
     if: |
       always() &&
+      inputs.runner_config != '4-gpu-gb300' &&
       (fromJson(inputs.caller_inputs).runner_filter == null ||
        fromJson(inputs.caller_inputs).runner_filter == '' ||
        fromJson(inputs.caller_inputs).runner_filter == 'all' ||
diff --git a/.github/workflows/nightly-test-nvidia.yml b/.github/workflows/nightly-test-nvidia.yml
index a3e4e2c5294e..325c7293a9c4 100644
--- a/.github/workflows/nightly-test-nvidia.yml
+++ b/.github/workflows/nightly-test-nvidia.yml
@@ -23,7 +23,7 @@ on:
           - '2-gpu-large'
           - '4-gpu-h100'
           - '4-gpu-b200'
-          - '4-gpu-gb300'
+          # - '4-gpu-gb300'  # Temporarily disabled while the GB300 runner is unavailable.
           - '8-gpu-h200'
           - '8-gpu-b200'
           - 'diffusion'
diff --git a/.github/workflows/release-whl-deepgemm.yml b/.github/workflows/release-whl-deepgemm.yml
index 7037bce67b6f..284eda2969f7 100644
--- a/.github/workflows/release-whl-deepgemm.yml
+++ b/.github/workflows/release-whl-deepgemm.yml
@@ -114,10 +114,11 @@ jobs:
           # - arch_label: sm120
           #   runner: 1-gpu-5090
           #   wheel_arch: x86_64
-          - arch_label: sm100-aarch64
-            runner: 4-gpu-gb300
-            wheel_arch: aarch64
-            timeout: 180
+          # Temporarily disabled while the GB300 runner is unavailable; the aarch64 wheel still publishes untested.
+          # - arch_label: sm100-aarch64
+          #   runner: 4-gpu-gb300
+          #   wheel_arch: aarch64
+          #   timeout: 180
     runs-on: ${{ matrix.runner }}
     timeout-minutes: ${{ matrix.timeout }}
     steps:
diff --git a/.github/workflows/rerun-test.yml b/.github/workflows/rerun-test.yml
index 74190784431f..e3c83c8bc8f3 100644
--- a/.github/workflows/rerun-test.yml
+++ b/.github/workflows/rerun-test.yml
@@ -119,7 +119,8 @@ jobs:
   rerun-test-cuda:
     name: rerun-test-cuda (partition ${{ matrix.partition }})
     needs: prepare-partitions
-    if: inputs.mode == 'cuda'
+    # Temporarily reject reruns targeting the unavailable GB300 runner.
+    if: inputs.mode == 'cuda' && inputs.runs_on != '4-gpu-gb300'
     strategy:
       fail-fast: false
       matrix: ${{ fromJson(needs.prepare-partitions.outputs.matrix) }}
diff --git a/scripts/ci/utils/slash_command_handler.py b/scripts/ci/utils/slash_command_handler.py
index abfe8d54fa25..570661c2e470 100644
--- a/scripts/ci/utils/slash_command_handler.py
+++ b/scripts/ci/utils/slash_command_handler.py
@@ -24,6 +24,10 @@
 # (single path component under that dir, no whitespace/operators).
 _ALLOWED_INSTALL_SCRIPT = re.compile(r"^scripts/ci/cuda/[\w.-]+\.sh$")
 
+# Temporarily disabled while their runners are unavailable. rerun-test.yml
+# skips these too; rejecting here gives a clear reply instead of a skipped run.
+_DISABLED_RUNNER_CONFIGS = {"4-gpu-gb300"}
+
 # Configuration
 PERMISSIONS_FILE_PATH = ".github/CI_PERMISSIONS.json"
 TEST_GROUPS_FILE_PATH = "scripts/ci/rerun_test_groups.json"
@@ -991,6 +995,12 @@ def _resolve_runner_config(rc, full_path, suite):
             f"— not in scripts/ci/runner_configs.yml.\n\n"
             f"Known runner_configs: {known}",
         )
+    if rc in _DISABLED_RUNNER_CONFIGS:
+        return _dispatch_err(
+            suite,
+            f"runner_config `{rc}` in `{full_path}` is temporarily disabled "
+            f"while its runners are unavailable.",
+        )
     install_script = cfg["install"]
     if not _ALLOWED_INSTALL_SCRIPT.match(install_script):
         return _dispatch_err(