diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 000000000..4726f755b
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,18 @@
+<!--
+Pull request titles must follow conventional commits and are checked by CI:
+  feat|fix|docs|test|ci|chore(optional-scope): description
+Append `!` (for example `feat(neutron)!:`) for a change that requires operator
+action to upgrade.
+-->
+
+## What does this change do?
+
+## Upgrade impact
+
+- [ ] This change requires operator action to upgrade. If checked, add the
+      `upgrade-impact` label and a note under `Unreleased` in
+      `docs/release-notes/`. See [RELEASING.md](../RELEASING.md).
+
+Operator action means anything a deployment has to do beyond a normal resync:
+deploy repo or values changes, new or removed secrets, enabling or disabling a
+component, or a manual one-time step.
diff --git a/.github/workflows/release-note-check.yaml b/.github/workflows/release-note-check.yaml
new file mode 100644
index 000000000..ac9117de4
--- /dev/null
+++ b/.github/workflows/release-note-check.yaml
@@ -0,0 +1,73 @@
+name: Release note check
+
+# Deliberately has no `paths:` filter. A path-filtered workflow never reports a
+# status on pull requests that do not match it, which means it can never be made
+# a required check. Instead this always runs and short-circuits to success
+# unless the pull request has been flagged as upgrade-impacting, so the majority
+# of changes see no new friction.
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, edited, labeled, unlabeled]
+  merge_group:
+    types: [checks_requested]
+
+permissions: {}
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  release-note:
+    name: Release note for upgrade-impacting change
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      # merge_group events carry no pull request context, so there is nothing to
+      # check. Succeed so this workflow is still safe to mark as required.
+      - name: Skip on merge queue
+        if: github.event_name == 'merge_group'
+        run: echo "No pull request context on merge_group, skipping."
+
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+        if: github.event_name == 'pull_request'
+        with:
+          fetch-depth: 0
+
+      - name: Require a release note when flagged
+        if: github.event_name == 'pull_request'
+        env:
+          # The title is attacker-controlled, so pass it through the environment
+          # rather than interpolating it into the script.
+          PR_TITLE: ${{ github.event.pull_request.title }}
+          PR_LABELS: ${{ toJSON(github.event.pull_request.labels.*.name) }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          set -euo pipefail
+
+          flagged=0
+          if printf '%s' "$PR_TITLE" \
+              | grep -Eq '^(feat|fix|docs|test|ci|chore)(\([^)]*\))?!:'; then
+            flagged=1
+            echo "Flagged by '!' in the pull request title."
+          fi
+          if printf '%s' "$PR_LABELS" | grep -q '"upgrade-impact"'; then
+            flagged=1
+            echo "Flagged by the upgrade-impact label."
+          fi
+
+          if [ "$flagged" -eq 0 ]; then
+            echo "Not flagged as upgrade-impacting, nothing to check."
+            exit 0
+          fi
+
+          if git diff --name-only "$BASE_SHA" "$HEAD_SHA" \
+              | grep -q '^docs/release-notes/'; then
+            echo "Release note present."
+            exit 0
+          fi
+
+          echo "::error::This pull request is flagged as upgrade-impacting but does not touch docs/release-notes/. Add a bullet to the Unreleased section of the current series page describing what an operator has to do, or remove the upgrade-impact label and the '!' from the title if no operator action is needed."
+          exit 1
diff --git a/.markdownlint.yml b/.markdownlint.yml
index 5a3d241e2..6ea1054ab 100644
--- a/.markdownlint.yml
+++ b/.markdownlint.yml
@@ -23,9 +23,11 @@ MD013: false
 MD014: false
 
 # MD024 - Multiple headings with the same content
-# Multiple identical headings in the document are not allowed
-# This is disabled on all of the release notes pages in docs/release-notes
-MD024: true
+# Identical headings are only an error when they are siblings under the same
+# parent. The release notes pages in docs/release-notes repeat headings such as
+# "Action required" once per version section, which is intended.
+MD024:
+    siblings_only: true
 
 # MD033 - Inline HTML
 # Triggered when raw HTML is used in a markdown document
diff --git a/RELEASING.md b/RELEASING.md
new file mode 100644
index 000000000..5d2c4238d
--- /dev/null
+++ b/RELEASING.md
@@ -0,0 +1,199 @@
+# Releasing UnderStack
+
+Repository-wide `vX.Y.Z` tags are created **manually**. No workflow creates
+them. Pushing the tag triggers `containers.yaml` and `containers-openstack.yaml`,
+which publish container images tagged with the git ref.
+
+Per-artifact tags (`understackctl/vX.Y.Z`, `nautobotop-vX.Y.Z`,
+`kubectl-us-net/vX.Y.Z`, `ironic-hardware-exporter/vX.Y.Z`, `dexop-vX.Y.Z`) are
+released independently and are not covered here.
+
+## Where upgrade notes live
+
+Operator-facing upgrade notes live in `docs/release-notes/`, one page per minor
+series, listing versions newest-first. Anyone whose change requires operator
+action adds a bullet under `Unreleased` on the current series page **in the same
+pull request as the change**, and labels the pull request `upgrade-impact`.
+
+Two invariants:
+
+- There is **exactly one `Unreleased` section** across all series pages, always
+  on the highest-numbered page.
+- **Most releases will not need a note at all.** Tags are cut frequently and
+  usually carry nothing an operator has to act on. A version that requires no
+  operator action gets **no section**, and cutting it involves no docs change
+  whatsoever. Empty sections teach operators that these pages are not worth
+  opening, which is the one outcome that makes them useless.
+
+Because `understack_ref` defaults to `HEAD` and the docs site only publishes
+`main`, a note merged alongside its change is immediately visible to the
+deployments that track `main`. That is the reason notes are written up front
+rather than assembled at release time.
+
+## Cutting a patch release
+
+### 1. Review the diff for undocumented operator impact
+
+Not every operator-affecting change gets flagged. Before promoting the notes,
+compare the previous tag against `main` over the paths where impact hides:
+
+```bash
+git fetch --tags
+git diff v0.4.25..main --stat -- \
+  charts/argocd-understack/values.yaml \
+  charts/argocd-understack/templates/ \
+  components/images-openstack.yaml
+```
+
+Look specifically for:
+
+- new, renamed or removed `enabled:` keys under `global:` or `site:`
+- OpenStack-Helm `chartVersion` bumps, especially ones crossing a release
+  series (for example `2025.2` to `2026.1`)
+- OpenStack image series changes in `components/images-openstack.yaml`
+- added or removed `application-*.yaml` templates, or new services added to the
+  service list in `application-openstack-helm.yaml`
+
+Anything you find here that is not already under `Unreleased` is a gap. Add it
+now.
+
+### 2. Promote the `Unreleased` section
+
+**If every subsection under `Unreleased` still says `_Nothing yet._`, there is
+nothing to do here.** Leave the page alone and skip to step 3 to tag. This is
+the common case.
+
+Otherwise, in the current series page, for example `docs/release-notes/v0.4.md`:
+
+1. Change `## Unreleased` to `## v0.4.26` and add the metadata lines
+   (`**Released:**`, `**Impact:**`, `**Applies to:**`).
+2. Delete any subsection whose only content is `_Nothing yet._`.
+3. Insert a fresh `## Unreleased` block above it, copied from the template
+   below.
+
+Then open a pull request titled `docs: release notes for v0.4.26` and merge it
+before tagging, so the tag contains its own notes.
+
+### 3. Tag the release
+
+Tag the current tip of `main`:
+
+```bash
+git checkout main && git pull
+git tag -a v0.4.26 -m "v0.4.26"
+git push origin v0.4.26
+```
+
+### 4. Create the GitHub release
+
+Create the release from the tag with auto-generated notes. If this version got a
+section in step 2, add one line at the top of the body pointing at it:
+
+```markdown
+**Upgrading?** See the
+[v0.4.26 upgrade notes](https://rackerlabs.github.io/understack/release-notes/v0.4/#v0426).
+```
+
+If it got no section, leave the body as generated. Do not link a section that
+does not exist.
+
+### 5. Confirm the builds
+
+Check that `containers.yaml` and `containers-openstack.yaml` succeeded for the
+tag.
+
+## Cutting a minor release
+
+A new series always gets a page, whether or not the release itself has notes,
+because that page is where subsequent `Unreleased` notes go. Same as above, but
+first:
+
+1. Create `docs/release-notes/v0.5.md` with a `# Release Notes: v0.5.x`
+   heading.
+2. Move the `Unreleased` block out of `v0.4.md` into `v0.5.md`. If it has
+   content, promote that content to `## v0.5.0` and leave a fresh `Unreleased`
+   block above it. If it is empty, just leave the empty `Unreleased` block on
+   the new page. Either way `v0.4.md` ends up with no `Unreleased` section.
+3. Add `- release-notes/v0.5.md` to `properdocs.yml` **above** the v0.4 entry.
+   Forgetting this fails the docs build, which is intentional.
+4. Update the series table in `docs/release-notes/index.md`: mark v0.5.x
+   Current and v0.4.x Maintenance.
+5. Update the `Unreleased` anchor in the "If you deploy from `main`" callout in
+   `docs/release-notes/index.md` to point at the new page.
+
+## Section template
+
+Copy this for a new version section. Include only the subsections that apply
+and delete the rest: an empty `Rollback` heading is worse than no `Rollback`
+heading.
+
+Two authoring constraints in this repo. The `nl2br` extension is enabled, so a
+single newline inside a paragraph renders as a line break. And markdownlint sets
+`MD007: indent: 4`, so nested list items are indented by four spaces.
+
+````markdown
+## v0.4.26
+
+**Released:** 2026-08-11
+**Impact:** Action required
+**Applies to:** site clusters
+
+### Summary
+
+One or two sentences on what changed and why an operator has to care. Link the
+pull request or issue for the underlying detail.
+
+### Action required
+
+Ordered and copy-pasteable, in the order the steps must be performed.
+
+1. Do the first thing.
+
+    ```bash
+    kubectl -n openstack get pods
+    ```
+
+2. Do the second thing.
+
+### Deploy repo changes
+
+Show before and after, using the real path.
+
+```yaml title="$CLUSTER_NAME/deploy.yaml"
+site:
+  neutron:
+    enabled: true
+```
+
+### Secrets
+
+- **New:** `<secret-name>` in namespace `<ns>`, keys `<k1>`, `<k2>`.
+- **Removed:** `<secret-name>`, safe to delete after upgrading.
+
+### Chart and image versions
+
+- OpenStack-Helm `neutron` chart: `<old>` to `<new>`
+  (`charts/argocd-understack/values.yaml`).
+- `keystone` image series: `<old>` to `<new>`
+  (`components/images-openstack.yaml`). Series tags are moving tags rebuilt
+  from `main`, and `pull_policy` is `Always`, so a resync pulls the current
+  build.
+
+### Verification
+
+How an operator confirms the upgrade worked.
+
+```bash
+kubectl -n openstack get pods
+```
+
+### Rollback
+
+State honestly whether rollback is possible. If it is, set `understack_ref`
+back to `v0.4.25` and resync. If it is not, say so plainly and give the
+recovery path instead.
+
+### Known issues
+
+- None.
+````
diff --git a/docs/operator-guide/index.md b/docs/operator-guide/index.md
index 1bac29615..48d23dc78 100644
--- a/docs/operator-guide/index.md
+++ b/docs/operator-guide/index.md
@@ -33,6 +33,13 @@ clouds:
 In the above case `uc-prod-infra` would be the operator area while `uc-prod` would
 be the regular project area.
 
+## Upgrading
+
+- [Release Notes](../release-notes/index.md) - What you have to do to move a
+  deployment between versions. If you deploy from `main`, read the
+  [Unreleased section](../release-notes/v0.4.md#unreleased) of the current
+  series.
+
 ## Infrastructure Topics
 
 - [Gateway API Migration Guide](gateway-api.md) - Migration from ingress-nginx to Kubernetes Gateway API with Envoy Gateway
diff --git a/docs/release-notes/index.md b/docs/release-notes/index.md
new file mode 100644
index 000000000..b1c8c0c96
--- /dev/null
+++ b/docs/release-notes/index.md
@@ -0,0 +1,54 @@
+# Release Notes
+
+These pages document **what an operator has to do** to move a deployment from
+one version of UnderStack to another: required changes to your deployment
+repository, new or removed secrets, one-time manual steps, and how to roll
+back.
+
+They are deliberately **not** a changelog. For the full list of merged pull
+requests in a given tag, see the
+[GitHub releases page](https://github.com/rackerlabs/understack/releases).
+
+!!! tip "If you deploy from `main`"
+    The default deployment model sets `understack_ref: HEAD`, so most
+    deployments track `main` continuously rather than a tag. Read the
+    [Unreleased section](v0.4.md#unreleased) of the current series page. It
+    covers everything merged to `main` since the most recent tag, and it is
+    updated in the same pull request as the change it describes.
+
+## Series
+
+| Series | Status |
+| ------ | ------ |
+| [v0.4.x](v0.4.md) | Current |
+
+## How to read these pages
+
+- There is one page per **minor** series. Each page lists versions
+  newest-first.
+- **Only versions that require operator action get a section.** Most do not, so
+  most versions are absent from these pages. If a version has no section, it
+  needed nothing beyond a normal resync.
+- Each section states its **Impact** (`Action required` or `Informational`) and
+  which cluster types it **applies to**.
+
+## Pinning a version
+
+To upgrade deliberately rather than continuously, pin `understack_ref` to a tag
+in your cluster values file instead of leaving it at `HEAD`. See
+[ArgoCD Application Management](../operator-guide/argocd-helm-chart.md) for the
+full explanation of how refs are resolved.
+
+```yaml title="$CLUSTER_NAME/deploy.yaml"
+understack_ref: v0.4.26
+```
+
+## Related upgrade guides
+
+Some upgrades are large enough to warrant a standalone guide. Release notes link
+to these rather than duplicating them.
+
+- [Gateway API Migration Guide](../operator-guide/gateway-api.md) — moving from
+  ingress-nginx to Envoy Gateway.
+- [MariaDB Operator Upgrade Runbook](../operator-guide/mariadb-upgrade-runbook.md)
+  — upgrading the operator, with backup and restore steps.
diff --git a/docs/release-notes/v0.4.md b/docs/release-notes/v0.4.md
new file mode 100644
index 000000000..1510d9c88
--- /dev/null
+++ b/docs/release-notes/v0.4.md
@@ -0,0 +1,48 @@
+<!--
+Adding a note? Put a bullet under the matching subsection of "Unreleased"
+below, in the same pull request as your change, and label the PR
+`upgrade-impact`. Cutting a release? See RELEASING.md in the repository root
+for the section template and the promotion procedure.
+-->
+# Release Notes: v0.4.x
+
+Operator-facing upgrade notes for the v0.4 series, newest first. See the
+[Release Notes index](index.md) for how to read these pages.
+
+## Unreleased
+
+Changes merged to `main` but not yet in a tagged release. If you deploy with
+`understack_ref: HEAD`, this section applies to you now.
+
+### Action required
+
+- _Nothing yet._
+
+### Deploy repo changes
+
+- _Nothing yet._
+
+### Deprecations and removals
+
+- _Nothing yet._
+
+### Notes
+
+- _Nothing yet._
+
+## v0.4.25 and earlier
+
+Per-version upgrade notes begin with **v0.4.26**. For earlier versions the only
+record is the auto-generated pull request list on the
+[GitHub releases page](https://github.com/rackerlabs/understack/releases).
+
+We have deliberately not reconstructed per-version notes for those releases:
+inferring operator impact from pull request titles after the fact produces
+confident-sounding instructions nobody has verified. The operator-affecting
+changes from before v0.4.26 that _are_ documented have their own guides:
+
+- [Gateway API Migration Guide](../operator-guide/gateway-api.md) — the move
+  from ingress-nginx to Envoy Gateway. Required if your deployment still runs
+  ingress-nginx.
+- [MariaDB Operator Upgrade Runbook](../operator-guide/mariadb-upgrade-runbook.md)
+  — upgrading the MariaDB operator, including backup and restore.
diff --git a/properdocs.yml b/properdocs.yml
index 1cc2c637a..6c8a27329 100644
--- a/properdocs.yml
+++ b/properdocs.yml
@@ -262,6 +262,13 @@ nav:
     - 'Scripts and Tools':
       - operator-guide/scripts.md
       - operator-guide/understackctl.md
+  # Keep this list newest-series-first and maintain it by hand. Do not switch it
+  # to include_dir_to_nav: that plugin only does an ascending ASCII sort, so
+  # v0.10.md would sort before v0.9.md, and its reverse toggle is global and
+  # would also flip the generated Workflows section.
+  - 'Release Notes':
+    - release-notes/index.md
+    - release-notes/v0.4.md
   - 'User Guide':
     - user-guide/index.md
     - user-guide/openstack-cli.md