diff --git a/.github/workflows/nightly-xr-ai-test.yml b/.github/workflows/nightly-xr-ai-test.yml
index d69ea2996..41f7d4800 100644
--- a/.github/workflows/nightly-xr-ai-test.yml
+++ b/.github/workflows/nightly-xr-ai-test.yml
@@ -8,9 +8,11 @@ name: nightly XR AI test
 # the default `tests` workflow (ubuntu-latest). Mirrors the local
 # `tests/run_local_gpu_tests.sh` entry point.
 #
-# Setup note: the GPU runner's Docker needs the NVIDIA runtime registered
-# (`sudo nvidia-ctk runtime configure --runtime=docker`); without it the
-# vLLM tests fail at container launch.
+# Setup notes:
+# - The GPU runner's Docker needs the NVIDIA runtime registered
+#   (`sudo nvidia-ctk runtime configure --runtime=docker`).
+# - The repository needs an Actions secret named `NGC_API_KEY`, backed by an
+#   NGC Personal or Service Key with NGC Catalog access.
 
 on:
   schedule:
@@ -44,6 +46,13 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Configure isolated Docker credentials
+        run: |
+          set -euo pipefail
+          docker_config="$RUNNER_TEMP/xr-ai-docker-${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}"
+          install -d -m 0700 "$docker_config"
+          echo "DOCKER_CONFIG=$docker_config" >> "$GITHUB_ENV"
+
       - name: Discover CUDA toolkit
         # Prefer CUDA 13.0 (current target), but fall back through the
         # usual symlinks and finally whatever `nvcc` is on PATH so we
@@ -86,6 +95,25 @@ jobs:
           nvcc --version
           nvcc --list-gpu-arch | grep compute_89
 
+      - name: Authenticate to NGC
+        if: >-
+          github.event_name != 'pull_request'
+          || github.event.pull_request.head.repo.full_name == github.repository
+        env:
+          NGC_API_KEY: ${{ secrets.NGC_API_KEY }}
+        run: |
+          set -euo pipefail
+          if [[ -z "${NGC_API_KEY:-}" ]]; then
+            echo "::error::NGC_API_KEY repository secret is required for nvcr.io images"
+            exit 1
+          fi
+          printf '%s' "$NGC_API_KEY" | docker login nvcr.io \
+            --username '$oauthtoken' --password-stdin
+          if ! docker manifest inspect nvcr.io/nvidia/vllm:26.04-py3 >/dev/null; then
+            echo "::error::NGC_API_KEY must grant NGC Catalog access to nvidia/vllm"
+            exit 1
+          fi
+
       - name: Install uv
         uses: astral-sh/setup-uv@caf0cab7a618c569241d31dcd442f54681755d39  # v3
         with:
@@ -169,6 +197,15 @@ jobs:
             echo "No xr-ai-vllm-* containers to remove."
           fi
 
+      - name: Remove NGC credentials
+        if: always()
+        run: |
+          set -u
+          if [[ -n "${DOCKER_CONFIG:-}" ]]; then
+            rm -rf -- "$DOCKER_CONFIG"
+          fi
+          DOCKER_CONFIG="$HOME/.docker" docker logout nvcr.io || true
+
   notify:
     name: alert on failure
     needs: [pytest]
diff --git a/docs/changelog.md b/docs/changelog.md
index 9cabc2e36..4cb434d9a 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -18,6 +18,17 @@ allowing a valid command to survive noisy STT preambles without sending
 background speech to the agent. Commas, semicolons, URLs, and ordinary
 mid-sentence mentions remain non-matches to limit false wakes.
 
+### 2026-08-12 — Nightly GPU CI authenticates to NGC explicitly
+
+The nightly GPU workflow logs in to `nvcr.io` with the repository's
+`NGC_API_KEY` before setup and tests begin, then verifies access to the vLLM
+image manifest. A job-scoped, per-run `DOCKER_CONFIG` is inherited by model
+subprocesses without exposing the key to pytest; fork pull requests run without
+the secret. CI authenticates directly because `_maybe_ngc_login()` checks the
+default Docker config rather than this isolated path. Always-run cleanup deletes
+the isolated config and removes credentials leaked to the runner-global config
+by earlier workflow revisions.
+
 ### 2026-08-12 — NeMo Agent Toolkit compatibility is retired
 
 All surviving capabilities now use native `xr-ai-tools` contracts. OpenXR,
diff --git a/docs/credentials.md b/docs/credentials.md
index ce5c88444..1c473722a 100644
--- a/docs/credentials.md
+++ b/docs/credentials.md
@@ -71,6 +71,12 @@ set it ahead of time:
 export NGC_API_KEY=nvapi-xxx
 ```
 
+Nightly GPU CI reads the same value from a required repository Actions secret
+named `NGC_API_KEY`. Use an NGC Personal or Service Key authorized for **NGC
+Catalog**; an endpoint-only NVIDIA API key cannot pull `nvcr.io` images.
+Scheduled, manual, and same-repository pull-request runs use the key only in the
+NGC authentication step; fork pull requests do not receive the secret.
+
 ## How a token is resolved
 
 `load_credentials()` (always) and `ensure_credentials()` (NGC only) resolve in
diff --git a/docs/source/getting_started/credentials.md b/docs/source/getting_started/credentials.md
index e720250c2..4d94423f8 100644
--- a/docs/source/getting_started/credentials.md
+++ b/docs/source/getting_started/credentials.md
@@ -72,6 +72,12 @@ set it ahead of time:
 export NGC_API_KEY=nvapi-xxx
 ```
 
+Nightly GPU CI reads the same value from a required repository Actions secret
+named `NGC_API_KEY`. Use an NGC Personal or Service Key authorized for **NGC
+Catalog**; an endpoint-only NVIDIA API key cannot pull `nvcr.io` images.
+Scheduled, manual, and same-repository pull-request runs use the key only in the
+NGC authentication step; fork pull requests do not receive the secret.
+
 ## How a token is resolved
 
 `load_credentials()` (always) and `ensure_credentials()` (NGC only) resolve in