diff --git a/.github/workflows/actionlint.yml b/.github/workflows/actionlint.yml
index 6681826..1b8fa45 100644
--- a/.github/workflows/actionlint.yml
+++ b/.github/workflows/actionlint.yml
@@ -19,7 +19,7 @@ permissions:
 
 jobs:
   actionlint:
-    runs-on: gus-small
+    runs-on: ubuntu-latest
     steps:
       - name: Check out repository
         uses: actions/checkout@v7.0.1
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 13a3409..a7850cc 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -21,7 +21,7 @@ permissions:
 
 jobs:
   pytest:
-    runs-on: gus-small
+    runs-on: ubuntu-latest
     steps:
       - name: Check out repository
         uses: actions/checkout@v7.0.1
diff --git a/README.md b/README.md
index 776033a..5b2ad72 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,8 @@ Reusable GitHub Actions and workflows for Climate Resource repositories.
 | [bump-version](./bump-version)   | Bump version with `uv version`, towncrier changelog, tag, dev-commit |
 | [draft-release](./draft-release) | Create a draft GitHub release with notes and artifacts               |
 
+[notify-flux](./notify-flux) notifies Flux after an image is published.
+
 ## Reusable workflows
 
 | Workflow                                                       | Trigger         | Description                                                              |
diff --git a/changelog/31.feature.md b/changelog/31.feature.md
new file mode 100644
index 0000000..388ddeb
--- /dev/null
+++ b/changelog/31.feature.md
@@ -0,0 +1 @@
+Adds a shared action to notify Flux after publishing a service image.
diff --git a/notify-flux/README.md b/notify-flux/README.md
new file mode 100644
index 0000000..5b1271e
--- /dev/null
+++ b/notify-flux/README.md
@@ -0,0 +1,20 @@
+# Notify Flux
+
+Calls a Flux `generic-hmac` Receiver after an image has been pushed.
+The request body contains the published commit SHA.
+The action needs Python 3 on the runner.
+
+```yaml
+- name: Notify Flux
+  if: ${{ !github.event.pull_request.head.repo.fork }}
+  uses: climate-resource/github-actions/notify-flux@v1
+  with:
+    receiver-url: ${{ secrets.FLUX_RECEIVER_URL }}
+    receiver-token: ${{ secrets.FLUX_RECEIVER_TOKEN }}
+    sha: ${{ github.event.pull_request.head.sha || github.sha }}
+```
+
+Run this step only after a successful image push.
+If both secrets are absent, the action reports that Flux will poll instead.
+A partially configured receiver or a failed request fails the step.
+The action does not print the URL, token, signature or response body.
diff --git a/notify-flux/action.yml b/notify-flux/action.yml
new file mode 100644
index 0000000..8f17bab
--- /dev/null
+++ b/notify-flux/action.yml
@@ -0,0 +1,23 @@
+name: Notify Flux
+description: Notify a generic-hmac Flux Receiver after an image is published.
+inputs:
+  receiver-url:
+    description: Full Flux Receiver URL from FLUX_RECEIVER_URL.
+    required: false
+  receiver-token:
+    description: HMAC token from FLUX_RECEIVER_TOKEN.
+    required: false
+  sha:
+    description: Commit whose image was published.
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Notify Flux
+      shell: bash
+      env:
+        FLUX_RECEIVER_URL: ${{ inputs.receiver-url }}
+        FLUX_RECEIVER_TOKEN: ${{ inputs.receiver-token }}
+        BUILD_SHA: ${{ inputs.sha }}
+        ACTION_PATH: ${{ github.action_path }}
+      run: python3 "$ACTION_PATH/notify.py"
diff --git a/notify-flux/notify.py b/notify-flux/notify.py
new file mode 100644
index 0000000..f0a968c
--- /dev/null
+++ b/notify-flux/notify.py
@@ -0,0 +1,41 @@
+"""Send the published commit to a Flux generic-hmac Receiver."""
+
+import hashlib
+import hmac
+import json
+import os
+import sys
+import urllib.error
+import urllib.request
+
+
+def notify(url, token, sha):
+    if not url and not token:
+        print("::notice::Flux receiver secrets are absent. Flux will poll instead.")
+        return 0
+    if not url or not token:
+        print("::error::Set both FLUX_RECEIVER_URL and FLUX_RECEIVER_TOKEN.")
+        return 1
+    if not url.startswith("https://") or not sha:
+        print("::error::Flux notification requires an HTTPS receiver URL and a commit SHA.")
+        return 1
+    body = json.dumps({"sha": sha}, separators=(",", ":")).encode()
+    signature = hmac.new(token.encode(), body, hashlib.sha256).hexdigest()
+    request = urllib.request.Request(
+        url,
+        data=body,
+        headers={"Content-Type": "application/json", "X-Signature": f"sha256={signature}"},
+        method="POST",
+    )
+    try:
+        with urllib.request.urlopen(request, timeout=30):
+            pass
+    except (urllib.error.URLError, TimeoutError):
+        print("::error::Flux notification failed. Check Receiver readiness and secret configuration.")
+        return 1
+    print("Flux notified of the published image.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(notify(os.getenv("FLUX_RECEIVER_URL", ""), os.getenv("FLUX_RECEIVER_TOKEN", ""), os.getenv("BUILD_SHA", "")))
diff --git a/tests/test_notify_flux.py b/tests/test_notify_flux.py
new file mode 100644
index 0000000..b53f40e
--- /dev/null
+++ b/tests/test_notify_flux.py
@@ -0,0 +1,52 @@
+import hashlib
+import hmac
+import importlib.util
+import pathlib
+import urllib.error
+from unittest.mock import MagicMock
+
+import pytest
+
+spec = importlib.util.spec_from_file_location(
+    "notify_flux", pathlib.Path(__file__).resolve().parents[1] / "notify-flux/notify.py"
+)
+notify_flux = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(notify_flux)
+
+
+def test_signs_exact_request_body(monkeypatch):
+    send = MagicMock()
+    monkeypatch.setattr(notify_flux.urllib.request, "urlopen", send)
+    assert notify_flux.notify("https://flux.example/hook", "test-token", "abc123") == 0
+    request = send.call_args.args[0]
+    assert request.data == b'{"sha":"abc123"}'
+    assert request.method == "POST"
+    expected = hmac.new(b"test-token", request.data, hashlib.sha256).hexdigest()
+    assert request.get_header("X-signature") == f"sha256={expected}"
+    assert send.call_args.kwargs == {"timeout": 30}
+
+
+@pytest.mark.parametrize("url,token,sha,result", [
+    ("", "", "abc123", 0),
+    ("https://flux.example/hook", "", "abc123", 1),
+    ("", "test-token", "abc123", 1),
+    ("http://flux.example/hook", "test-token", "abc123", 1),
+    ("https://flux.example/hook", "test-token", "", 1),
+])
+def test_invalid_or_absent_configuration_never_sends(monkeypatch, url, token, sha, result):
+    send = MagicMock()
+    monkeypatch.setattr(notify_flux.urllib.request, "urlopen", send)
+    assert notify_flux.notify(url, token, sha) == result
+    send.assert_not_called()
+
+
+def test_failure_does_not_print_credentials(monkeypatch, capsys):
+    url = "https://flux.example/private-hook"
+    token = "test-private-token"
+    send = MagicMock(side_effect=urllib.error.URLError(url + token))
+    monkeypatch.setattr(notify_flux.urllib.request, "urlopen", send)
+    assert notify_flux.notify(url, token, "abc123") == 1
+    output = capsys.readouterr().out
+    assert url not in output
+    assert token not in output
+    assert "::error::" in output