diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 4b25313f9..bf7c7a1e4 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -369,6 +369,106 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+  # Signs the UPM package with Unity's UPM CLI using service-account credentials,
+  # then attaches the signed .tgz to the just-created GitHub Release.
+  #
+  # OpenUPM picks up the signed tarball when its listing has `trackingMode: githubRelease`
+  # (see docs/openupm-signing.md for the cross-repo OpenUPM listing change). Until then,
+  # OpenUPM continues to pack from git and ships unsigned packages — the asset attached
+  # here is still uploaded for verification.
+  #
+  # Required repo secrets (configure via `gh secret set --repo IvanMurzak/Unity-MCP <NAME>`):
+  #   - UPM_SERVICE_ACCOUNT_KEY_ID
+  #   - UPM_SERVICE_ACCOUNT_KEY_SECRET
+  #   - UPM_ORG_ID
+  # If any are missing the job soft-fails with `continue-on-error: true` so an absent
+  # signing key never blocks the release pipeline (the upstream release flow still ships).
+  # See https://openupm.com/docs/signing-upm-packages.html for the procedure.
+  sign-and-publish-upm:
+    runs-on: ubuntu-latest
+    needs: release-unity-plugin
+    if: needs.release-unity-plugin.outputs.success == 'true'
+    continue-on-error: true
+    env:
+      UPM_SERVICE_ACCOUNT_KEY_ID: ${{ secrets.UPM_SERVICE_ACCOUNT_KEY_ID }}
+      UPM_SERVICE_ACCOUNT_KEY_SECRET: ${{ secrets.UPM_SERVICE_ACCOUNT_KEY_SECRET }}
+      UPM_ORG_ID: ${{ secrets.UPM_ORG_ID }}
+      PACKAGE_DIR: Unity-MCP-Plugin/Packages/com.ivanmurzak.unity.mcp
+      DIST_DIR: /tmp/signed-upm-dist
+    steps:
+      - name: Verify signing secrets are configured
+        run: |
+          missing=()
+          [ -z "$UPM_SERVICE_ACCOUNT_KEY_ID" ]     && missing+=("UPM_SERVICE_ACCOUNT_KEY_ID")
+          [ -z "$UPM_SERVICE_ACCOUNT_KEY_SECRET" ] && missing+=("UPM_SERVICE_ACCOUNT_KEY_SECRET")
+          [ -z "$UPM_ORG_ID" ]                     && missing+=("UPM_ORG_ID")
+          if [ "${#missing[@]}" -ne 0 ]; then
+            printf '::warning::UPM signing secrets are not configured (%s); skipping signing. See docs/openupm-signing.md.\n' "${missing[*]}"
+            # Exit non-zero so subsequent steps short-circuit; continue-on-error at the
+            # job level keeps the overall release pipeline green.
+            exit 1
+          fi
+
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Log package metadata
+        run: |
+          package_name="$(jq -r '.name' "$PACKAGE_DIR/package.json")"
+          package_version="$(jq -r '.version' "$PACKAGE_DIR/package.json")"
+
+          printf 'Package name: %s\n' "$package_name"
+          printf 'Package version: %s\n' "$package_version"
+
+      - name: Install Unity UPM CLI
+        run: |
+          curl -fsSL https://cdn.packages.unity.com/upm-cli/install.sh -o install.sh
+          bash install.sh
+          echo "$HOME/.upm/bin" >> "$GITHUB_PATH"
+
+      - name: Verify Unity UPM CLI
+        run: upm --help
+
+      - name: Sign package
+        run: |
+          mkdir -p "$DIST_DIR"
+          upm pack "./$PACKAGE_DIR" --organization-id "$UPM_ORG_ID" --destination "$DIST_DIR"
+
+      - name: Verify signed package contains attestation
+        run: |
+          shopt -s nullglob
+          archives=("$DIST_DIR"/*.tgz "$DIST_DIR"/*.tar.gz)
+          if [ "${#archives[@]}" -ne 1 ]; then
+            printf 'Expected exactly one signed package archive, found %s: %s\n' "${#archives[@]}" "${archives[*]:-<none>}" >&2
+            exit 1
+          fi
+
+          archive="${archives[0]}"
+          archive_basename="$(basename "$archive")"
+          # OpenUPM consumes the asset via the `githubReleaseAssetName: 'com.ivanmurzak.unity.mcp-'`
+          # prefix documented in docs/openupm-signing.md. Enforce the contract here so a future
+          # `upm pack` naming change fails CI loudly instead of silently breaking OpenUPM pickup.
+          if [[ "$archive_basename" != com.ivanmurzak.unity.mcp-* ]]; then
+            printf 'Signed archive basename %q does not begin with the OpenUPM-expected prefix com.ivanmurzak.unity.mcp- (see docs/openupm-signing.md)\n' "$archive_basename" >&2
+            exit 1
+          fi
+
+          archive_entries="$(tar -tzf "$archive")"
+          grep -qx 'package/package.json'      <<<"$archive_entries"
+          grep -qx 'package/.attestation.p7m'  <<<"$archive_entries"
+
+          echo "PACKAGE_ARCHIVE=$archive" >> "$GITHUB_ENV"
+          printf 'Signed archive: %s\n' "$archive_basename"
+          tar -xOzf "$archive" package/package.json | jq '{name, version}'
+
+      - name: Attach signed package to release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: ${{ env.PACKAGE_ARCHIVE }}
+          tag_name: ${{ needs.release-unity-plugin.outputs.version }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
   publish_discord:
     runs-on: ubuntu-latest
     needs:
diff --git a/docs/_sidebar.md b/docs/_sidebar.md
index 3eae84329..f087469fc 100644
--- a/docs/_sidebar.md
+++ b/docs/_sidebar.md
@@ -16,6 +16,7 @@
 - **Development**
   - [Development Guide](/dev/Development.md)
   - [Version Management](/version-management.md)
+  - [OpenUPM Package Signing](/openupm-signing.md)
   - [Architecture](/#how-unity-mcp-architecture-works)
 
 - **Languages**
diff --git a/docs/openupm-signing.md b/docs/openupm-signing.md
new file mode 100644
index 000000000..907a3791b
--- /dev/null
+++ b/docs/openupm-signing.md
@@ -0,0 +1,136 @@
+# OpenUPM Package Signing
+
+Unity 6.3 introduced a package-signature check that surfaces a trust warning for
+unsigned UPM packages installed from third-party registries (including OpenUPM).
+This document describes how `IvanMurzak/Unity-MCP` signs its
+`com.ivanmurzak.unity.mcp` package so the warning no longer appears in Unity 6.3+.
+
+Tracks issue [#414](https://github.com/IvanMurzak/Unity-MCP/issues/414).
+
+## How signing works
+
+OpenUPM does **not** sign packages on behalf of authors — each package author runs
+the signing flow in their own CI using a Unity organization's service account. The
+signed `.tgz` is uploaded as a GitHub Release asset, and OpenUPM picks it up when
+the package's listing has `trackingMode: githubRelease`.
+
+References:
+- <https://openupm.com/docs/signing-upm-packages.html>
+- <https://openupm.com/blog/signing-upm-packages-with-openupm/>
+- Reference workflow / repo layout: <https://github.com/openupm/com.example.signed-upm>
+
+## What this repo ships
+
+The signing step is implemented as the `sign-and-publish-upm` job in
+[`.github/workflows/release.yml`](../.github/workflows/release.yml). It runs on
+every successful version-bump release (the same trigger as `publish-mcp-server`
+and `publish-unity-installer`), packs the package at
+`Unity-MCP-Plugin/Packages/com.ivanmurzak.unity.mcp/` with Unity's UPM CLI, and
+attaches the resulting signed `.tgz` to the release tag.
+
+The job is declared `continue-on-error: true` and exits early with a warning if
+the required Unity-org secrets are not configured — so until the secrets are in
+place the existing release flow continues to ship unchanged.
+
+## One-time setup (repository owner)
+
+These steps land outside this PR — they are operational, not code changes.
+
+### 1. Create a Unity organization service account
+
+A Unity organization is required to obtain UPM signing credentials (the
+individual / personal Unity license cannot sign packages).
+
+1. Go to the [Unity Cloud Dashboard](https://cloud.unity.com/) and either create
+   an organization or use an existing one you own.
+2. Inside the organization settings, create a service account dedicated to
+   package signing.
+3. Grant the service account the **package signing** permission for the
+   organization.
+4. Generate a service-account key — record the `Key ID`, the `Key Secret`, and
+   the organization's `Org ID`. The secret is shown only once.
+
+### 2. Add the three GitHub repository secrets
+
+In this repo's Settings → Secrets and variables → Actions, add:
+
+| Secret name                       | Value                                |
+| --------------------------------- | ------------------------------------ |
+| `UPM_SERVICE_ACCOUNT_KEY_ID`      | Service account key ID               |
+| `UPM_SERVICE_ACCOUNT_KEY_SECRET`  | Service account key secret           |
+| `UPM_ORG_ID`                      | Unity organization ID                |
+
+CLI equivalent:
+
+```bash
+gh secret set UPM_SERVICE_ACCOUNT_KEY_ID     --repo IvanMurzak/Unity-MCP
+gh secret set UPM_SERVICE_ACCOUNT_KEY_SECRET --repo IvanMurzak/Unity-MCP
+gh secret set UPM_ORG_ID                     --repo IvanMurzak/Unity-MCP
+```
+
+### 3. File the OpenUPM listing change
+
+OpenUPM's package listing for `com.ivanmurzak.unity.mcp` currently has
+`trackingMode: git`, which makes OpenUPM pack and serve unsigned tarballs from
+the repository's git tags. To make OpenUPM serve the signed tarball that the
+workflow now uploads, the listing must be flipped to `trackingMode: githubRelease`.
+
+The listing lives in the [openupm/openupm](https://github.com/openupm/openupm)
+repository at `data/packages/com.ivanmurzak.unity.mcp.yml`. Open a PR there
+changing:
+
+```yaml
+trackingMode: git
+```
+
+to:
+
+```yaml
+trackingMode: githubRelease
+```
+
+Per the OpenUPM blog, switch `trackingMode` to `githubRelease` **before** the
+first signed release ships, so OpenUPM does not race-publish the unsigned git
+tag in parallel.
+
+Also set `githubReleaseAssetName` so OpenUPM picks the signed tarball by
+filename prefix rather than guessing from the asset list. The release already
+ships `.unitypackage` and multiple server `.zip` assets, and may add more
+`.tgz` assets later (e.g. signing a second package), so the prefix guard
+prevents a future-breaking failure mode:
+
+```yaml
+githubReleaseAssetName: 'com.ivanmurzak.unity.mcp-'
+```
+
+## Verifying signing worked
+
+After the next release that runs with the secrets in place:
+
+1. Go to the [release page](https://github.com/IvanMurzak/Unity-MCP/releases)
+   for the new version and confirm a `com.ivanmurzak.unity.mcp-<version>.tgz`
+   asset is attached alongside the existing `.unitypackage` and server `.zip`s.
+2. Inspect the tarball locally to confirm it contains the signing attestation:
+
+   ```bash
+   curl -fsSL -o package.tgz \
+     https://github.com/IvanMurzak/Unity-MCP/releases/download/<version>/com.ivanmurzak.unity.mcp-<version>.tgz
+   tar -tzf package.tgz | grep '\.attestation\.p7m$'
+   # expected: package/.attestation.p7m
+   ```
+
+3. Once the OpenUPM listing change merges, install the package in Unity 6.3+
+   from OpenUPM and confirm the unsigned-package warning no longer appears.
+
+## Troubleshooting
+
+- **Job is skipped with warning "UPM signing secrets are not configured"** —
+  expected when the three secrets are not yet set. Complete the
+  "One-time setup" steps above.
+- **`upm pack` fails with an authentication error** — the service account key
+  is invalid or lacks the package-signing permission. Regenerate the key in the
+  Unity org dashboard and re-set the GitHub secrets.
+- **The release contains the `.tgz` but Unity 6.3 still shows the warning** —
+  the OpenUPM listing is still on `trackingMode: git` (OpenUPM is serving the
+  unsigned git-packed version, not the release asset). File the
+  `openupm/openupm` PR described above.