diff --git a/.github/workflows/cerberus-notify.yml b/.github/workflows/cerberus-notify.yml
index 4f68cc76..690613f6 100644
--- a/.github/workflows/cerberus-notify.yml
+++ b/.github/workflows/cerberus-notify.yml
@@ -22,12 +22,20 @@ name: Cerberus notify
 # deleted with the GitLab files, was built around GitLab's CI_* variables, and
 # predates the `platform` field.
 #
-# Prerequisite: CERBERUS_LAMBDA_URL must reach this repo as a REPO-level secret.
-# The org-level copy is visibility=private, which excludes this PUBLIC repo, and
-# widening it is not an option: the Cerberus endpoint is unauthenticated, so the
-# URL is the whole capability. Until the pulumi-infra change applies, this
-# workflow warns and exits 0 rather than adding a second red job to an already
-# failed run -- the annotation is the signal.
+# Prerequisites: CERBERUS_LAMBDA_URL and CERBERUS_API_TOKEN must both reach this
+# repo as REPO-level secrets. The org-level copies are visibility=private, which
+# excludes this PUBLIC repo. pulumi-infra provisions the pair together
+# (github/repoVariables/resources.yaml). If either is missing this workflow warns
+# and exits 0 rather than adding a second red job to an already failed run -- the
+# annotation is the signal.
+#
+# The bearer token is not optional going forward. StackVista/cerberus#4
+# (STAC-24889) adds `Authorization: Bearer <ssm:/cerberus/api-token>` verification
+# to every non-Slack request; before it, the endpoint was entirely
+# unauthenticated. Sending the header is forward-compatible -- the currently
+# deployed Lambda ignores unknown headers -- so this works either side of that
+# deploy. Without it, the first master failure after cerberus#4 ships would get a
+# 401 and no Slack message.
 #
 # The Slack channel is deliberately not sent. Cerberus resolves it as
 # `util.GetOrDefault(req.Context, "channel", s.Channel)`, and GetOrDefault treats
@@ -48,6 +56,8 @@ on:
       # step's guard can warn -- the failure mode this workflow exists to avoid.
       CERBERUS_LAMBDA_URL:
         required: false
+      CERBERUS_API_TOKEN:
+        required: false
 
 # Nothing here reads the repository; the payload is built entirely from the
 # github context.
@@ -62,6 +72,7 @@ jobs:
       - name: Post the failure to Cerberus
         env:
           CERBERUS_LAMBDA_URL: ${{ secrets.CERBERUS_LAMBDA_URL }}
+          CERBERUS_API_TOKEN: ${{ secrets.CERBERUS_API_TOKEN }}
           REPOSITORY: ${{ github.repository }}
           BRANCH: ${{ github.ref_name }}
           PIPELINE: ${{ github.run_id }}
@@ -71,16 +82,20 @@ jobs:
         run: |
           set -euo pipefail
 
-          if [ -z "${CERBERUS_LAMBDA_URL}" ]; then
-            echo "::warning title=Cerberus not configured::CERBERUS_LAMBDA_URL is not visible to this repo, so the ${SUITE} failure was not reported to Slack. Needs the repo-level secret from pulumi-infra (STAC-25519)."
+          if [ -z "${CERBERUS_LAMBDA_URL}" ] || [ -z "${CERBERUS_API_TOKEN}" ]; then
+            echo "::warning title=Cerberus not configured::CERBERUS_LAMBDA_URL and/or CERBERUS_API_TOKEN is not visible to this repo, so the ${SUITE} failure was not reported to Slack. Both are provisioned as repo-level secrets by pulumi-infra (STAC-25519)."
             exit 0
           fi
 
           COMMIT_TITLE=$(printf '%s' "${COMMIT_MESSAGE}" | head -n1)
 
-          curl --verbose --fail \
+          # Not --verbose: it echoes request headers, and the Authorization
+          # header carries the shared token. GitHub would mask it, but not
+          # emitting it is better than relying on masking.
+          curl --fail --silent --show-error \
             -X POST "${CERBERUS_LAMBDA_URL}" \
             -H "Content-Type: application/json" \
+            -H "Authorization: Bearer ${CERBERUS_API_TOKEN}" \
             -d "$(jq -n \
               --arg repo "${REPOSITORY}" \
               --arg branch "${BRANCH}" \
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6879fa09..de1f801e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -348,3 +348,4 @@ jobs:
       suite: build
     secrets:
       CERBERUS_LAMBDA_URL: ${{ secrets.CERBERUS_LAMBDA_URL }}
+      CERBERUS_API_TOKEN: ${{ secrets.CERBERUS_API_TOKEN }}