diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 47c98438..a7a836e2 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -9,3 +9,6 @@ from branches in `PolicyEngine/policyengine.py`; never create fork PRs.
 
 For repository-wide API, testing, documentation, release, or package-boundary
 changes, read `docs/engineering/skills/repository-guidance.md`.
+
+For certified release-bundle updates or reviews, read
+`docs/engineering/skills/release-bundles.md`.
diff --git a/AGENTS.md b/AGENTS.md
index 7fbff1be..58cfd8b8 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -15,6 +15,9 @@ Before making or reviewing repository-wide API, testing, documentation, release,
 or package-boundary changes, read
 `docs/engineering/skills/repository-guidance.md`.
 
+Before updating or reviewing certified release bundles, read
+`docs/engineering/skills/release-bundles.md`.
+
 ## Repository Boundaries
 
 `policyengine.py` is the user-facing analysis package. It wraps
diff --git a/CLAUDE.md b/CLAUDE.md
index 4bcc4c72..0ab09ac5 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -19,3 +19,6 @@ Before opening, replacing, or sharing a PR, read
 Before making or reviewing repository-wide API, testing, documentation, release,
 or package-boundary changes, read
 `docs/engineering/skills/repository-guidance.md`.
+
+Before updating or reviewing certified release bundles, read
+`docs/engineering/skills/release-bundles.md`.
diff --git a/changelog.d/378.added.md b/changelog.d/378.added.md
new file mode 100644
index 00000000..a3299e0a
--- /dev/null
+++ b/changelog.d/378.added.md
@@ -0,0 +1 @@
+Add AI-facing release-bundle guidance for single-country refreshes and compatibility fallbacks.
diff --git a/docs/engineering/skills/README.md b/docs/engineering/skills/README.md
index 7351c077..4bed78b4 100644
--- a/docs/engineering/skills/README.md
+++ b/docs/engineering/skills/README.md
@@ -13,3 +13,5 @@ Current skills:
   changelog-fragment requirements, PR head verification, and title conventions.
 - `repository-guidance.md`: policyengine.py structure, commands, package
   boundaries, test expectations, and repo-specific anti-patterns.
+- `release-bundles.md`: certified release-bundle refresh workflow, model/data
+  compatibility gates, expected files, and bundle-specific tests.
diff --git a/docs/engineering/skills/release-bundles.md b/docs/engineering/skills/release-bundles.md
new file mode 100644
index 00000000..de68c808
--- /dev/null
+++ b/docs/engineering/skills/release-bundles.md
@@ -0,0 +1,91 @@
+# Release Bundles
+
+Use this skill when updating or reviewing a `policyengine.py` certified release
+bundle for US, UK, or both countries.
+
+## Core Rules
+
+Open release-bundle implementation work on a fresh branch from current `main`.
+If the checkout is dirty, use a clean worktree instead of overwriting unrelated
+changes.
+
+Do not hand-edit bundled release manifests for normal updates. Use the existing
+single-country refresh script so model wheels, data artifacts, `pyproject.toml`,
+and TRACE TROs move together:
+
+```bash
+python scripts/refresh_release_bundle.py --country us --model-version 1.715.2
+python scripts/refresh_release_bundle.py --country uk --model-version 2.89.0
+```
+
+When a new data release is part of the certification, pass it explicitly:
+
+```bash
+python scripts/refresh_release_bundle.py --country us \
+  --model-version 1.715.2 \
+  --data-version 1.115.5
+```
+
+There is no supported `all` mode. If a user asks to update both US and UK, run
+the single-country workflow for one country, inspect the result, then run it for
+the other country.
+
+UK data is private. Set `HUGGING_FACE_TOKEN` or `HF_TOKEN` before refreshing UK
+bundles.
+
+## Certification Order
+
+For one country, first attempt full bundle certification with the existing
+refresh script and a country data release manifest that supports the target
+model by exact build version or matching `data_build_fingerprint`.
+
+If full certification is not possible, the fallback is a country-data release
+manifest assertion through `compatible_model_packages`. This fallback must be
+created with the country data repo's release-manifest tooling, not by manually
+editing the `policyengine.py` bundle. Tell the user clearly that this fallback is
+only the data-release publisher claiming compatibility; there is currently no
+validation or verification proving that the setup actually works.
+
+For that fallback, use the country data repo's release-manifest builder or
+publishing path with `additional_compatible_specifiers` set to the target model
+specifier, for example `("==1.715.2",)` for US or `("==2.89.0",)` for UK.
+Publish the updated country data release manifest before touching the `.py`
+bundle.
+
+After a country-data fallback manifest is published, rerun
+`scripts/refresh_release_bundle.py` for that country and point at the updated
+data release manifest revision if needed.
+
+## Expected Files
+
+A real `.py` refresh should normally change only:
+
+- `src/policyengine/data/release_manifests/{country}.json`
+- `src/policyengine/data/release_manifests/{country}.trace.tro.jsonld`
+- `pyproject.toml`
+- `uv.lock`, only if the lockfile is intentionally refreshed
+- one Towncrier fragment under `changelog.d/`
+
+Unexpected files are a reason to stop and inspect the diff.
+
+## Testing
+
+For release-bundle script or manifest changes, run:
+
+```bash
+POLICYENGINE_SKIP_COUNTRY_IMPORTS=1 uv run pytest --noconftest \
+  tests/test_bundle_refresh.py
+
+uv run pytest \
+  tests/test_release_manifests.py \
+  tests/test_trace_tro.py
+```
+
+For a real data artifact change, also run and review snapshot diffs:
+
+```bash
+PE_UPDATE_SNAPSHOTS=1 uv run pytest tests/test_household_calculator_snapshot.py
+```
+
+Before opening a PR, run the standard repository checks from
+`repository-guidance.md`.