diff --git a/.github/workflows/reusable-build-package.yml b/.github/workflows/reusable-build-package.yml
new file mode 100644
index 0000000000000..f7c744af7c34a
--- /dev/null
+++ b/.github/workflows/reusable-build-package.yml
@@ -0,0 +1,60 @@
+##
+# A reusable workflow that builds and packages WordPress. The resulting package can be used to test upgrading and installing.
+##
+name: Build and package WordPress
+
+on:
+  workflow_call:
+
+# Disable permissions for all available scopes by default.
+# Any needed permissions should be configured at the job level.
+permissions: {}
+
+jobs:
+  # Builds and packages WordPress.
+  #
+  # Performs the following steps:
+  # - Checks out the repository.
+  # - Sets up Node.js.
+  # - Runs the build script.
+  # - Prepares the directory structure for the ZIP.
+  # - Creates a ZIP of the built files.
+  # - Uploads the ZIP as a GitHub Actions artifact.
+  build:
+    name: WordPress
+    permissions:
+      contents: read
+    runs-on: ubuntu-24.04
+    timeout-minutes: 20
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
+          persist-credentials: false
+
+      - name: Set up Node.js
+        uses: actions/setup-node@1d0ff469b7ec7b3cb9d8673fde0c81c44821de2a # v4.2.0
+        with:
+          node-version-file: '.nvmrc'
+          cache: npm
+
+      - name: Install npm Dependencies
+        run: npm ci
+
+      - name: Build WordPress
+        run: npm run build
+
+      - name: Prepare the directory structure for the ZIP
+        run: mv build wordpress
+
+      - name: Create ZIP of built files
+        run: zip -q -r develop.zip wordpress/.
+
+      - name: Upload ZIP as a GitHub Actions artifact
+        uses: actions/upload-artifact@65c4c4a1ddee5b72f698fdd19549f0f0fb45cf08 # v4.6.0
+        with:
+          name: wordpress-develop
+          path: develop.zip
+          if-no-files-found: error
diff --git a/.github/workflows/reusable-upgrade-testing.yml b/.github/workflows/reusable-upgrade-testing.yml
index 1c617ee91f36f..7b9f542041165 100644
--- a/.github/workflows/reusable-upgrade-testing.yml
+++ b/.github/workflows/reusable-upgrade-testing.yml
@@ -14,7 +14,7 @@ on:
         required: true
         type: 'string'
       new-version:
-        description: 'The version of WordPress to update to.'
+        description: 'The version of WordPress to update to. Use "latest" to update to the latest version, "develop" to update to the current branch, or provide a specific version number to update to.'
         type: 'string'
         default: 'latest'
       php:
@@ -49,8 +49,13 @@ jobs:
   # - Downloads the specified version of WordPress.
   # - Creates a `wp-config.php` file.
   # - Installs WordPress.
+  # - Checks the version of WordPress before the upgrade.
   # - Updates to the latest minor version.
+  # - Updates the database after the minor update.
+  # - Checks the version of WordPress after the minor update.
   # - Updates to the version of WordPress being tested.
+  # - Updates the database.
+  # - Checks the version of WordPress after the upgrade.
   upgrade-tests:
     name: ${{ inputs.wp }} to ${{ inputs.new-version }} / PHP ${{ inputs.php }} with ${{ 'mariadb' == inputs.db-type && 'MariaDB' || 'MySQL' }} ${{ inputs.db-version }}${{ inputs.multisite && ' multisite' || '' }}
     permissions: {}
@@ -96,11 +101,38 @@ jobs:
           --url=http://localhost/ --title="Upgrade Test" --admin_user=admin \
           --admin_password=password --admin_email=me@example.org --skip-email
 
+      - name: Pre-upgrade version check
+        run: wp core version
+
       - name: Update to the latest minor version
         run: wp core update --minor
 
+      - name: Update the database after the minor update
+        run: wp core update-db ${{ inputs.multisite && '--network' || '' }}
+
+      - name: Post-upgrade version check after the minor update
+        run: wp core version
+
+      - name: Download build artifact for the current branch
+        if: ${{ inputs.new-version == 'develop' }}
+        uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
+        with:
+          name: wordpress-develop
+
+      - name: Upgrade to WordPress at current branch
+        if: ${{ inputs.new-version == 'develop' }}
+        run: |
+          wp core update develop.zip
+
       - name: Upgrade to WordPress ${{ inputs.new-version }}
+        if: ${{ inputs.new-version != 'develop' }}
         run: |
           wp core update ${{ 'latest' != inputs.new-version && '--version="${WP_VERSION}"' || '' }}
         env:
           WP_VERSION: ${{ inputs.new-version }}
+
+      - name: Update the database
+        run: wp core update-db ${{ inputs.multisite && '--network' || '' }}
+
+      - name: Post-upgrade version check
+        run: wp core version
diff --git a/.github/workflows/upgrade-develop-testing.yml b/.github/workflows/upgrade-develop-testing.yml
new file mode 100644
index 0000000000000..edb57bc8d6e88
--- /dev/null
+++ b/.github/workflows/upgrade-develop-testing.yml
@@ -0,0 +1,129 @@
+# Confirms that updating WordPress using WP-CLI works successfully.
+#
+# This workflow tests upgrading from a previous version to the current wordpress-develop checkout, not to a version available on WordPress.org.
+name: Upgrade Develop Version Tests
+
+on:
+  push:
+    branches:
+      - trunk
+      - '6.[8-9]'
+      - '[7-9].[0-9]'
+    tags:
+      - '[0-9]+.[0-9]'
+      - '[0-9]+.[0-9].[0-9]+'
+    paths:
+      # Any change to a source PHP file should run checks.
+      - 'src/**.php'
+      # Confirm any changes to relevant workflow files.
+      - '.github/workflows/upgrade-develop-testing.yml'
+      - '.github/workflows/reusable-upgrade-testing.yml'
+  pull_request:
+    branches:
+      - trunk
+      - '6.[8-9]'
+      - '[7-9].[0-9]'
+    paths:
+      # Any change to a source PHP file should run checks.
+      - 'src/**.php'
+      # Confirm any changes to relevant workflow files.
+      - '.github/workflows/upgrade-develop-testing.yml'
+      - '.github/workflows/reusable-upgrade-testing.yml'
+  workflow_dispatch:
+
+# Cancels all previous workflow runs for pull requests that have not completed.
+concurrency:
+  # The concurrency group contains the workflow name and the branch name for pull requests
+  # or the commit hash for any other events.
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.head_ref || github.sha }}
+  cancel-in-progress: true
+
+# Disable permissions for all available scopes by default.
+# Any needed permissions should be configured at the job level.
+permissions: {}
+
+jobs:
+  # Build WordPress from the current branch ready for the upgrade tests.
+  build:
+    name: Build
+    uses: ./.github/workflows/reusable-build-package.yml
+    permissions:
+      contents: read
+
+  # Run upgrade tests for the current branch.
+  upgrade-tests-develop:
+    name: Upgrade from ${{ matrix.wp }}
+    uses: ./.github/workflows/reusable-upgrade-testing.yml
+    if: ${{ github.repository == 'WordPress/wordpress-develop' || github.event_name == 'pull_request' }}
+    needs: [ build ]
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ 'ubuntu-24.04' ]
+        php: [ '7.2', '8.4' ]
+        db-type: [ 'mysql' ]
+        db-version: [ '5.7', '8.4' ]
+        wp: [ '6.5', '6.6', '6.7' ]
+        multisite: [ false, true ]
+
+        exclude:
+          # The PHP <= 7.3/MySQL 8.4 jobs currently fail due to mysql_native_password being disabled by default. See https://core.trac.wordpress.org/ticket/61218.
+          - php: '7.2'
+            db-version: '8.4'
+    with:
+      os: ${{ matrix.os }}
+      php: ${{ matrix.php }}
+      db-type: ${{ matrix.db-type }}
+      db-version: ${{ matrix.db-version }}
+      wp: ${{ matrix.wp }}
+      new-version: develop
+      multisite: ${{ matrix.multisite }}
+
+  slack-notifications:
+    name: Slack Notifications
+    uses: ./.github/workflows/slack-notifications.yml
+    permissions:
+      actions: read
+      contents: read
+    needs: [ upgrade-tests-develop ]
+    if: ${{ github.repository == 'WordPress/wordpress-develop' && github.event_name != 'pull_request' && always() }}
+    with:
+      calling_status: ${{ contains( needs.*.result, 'cancelled' ) && 'cancelled' || contains( needs.*.result, 'failure' ) && 'failure' || 'success' }}
+    secrets:
+      SLACK_GHA_SUCCESS_WEBHOOK: ${{ secrets.SLACK_GHA_SUCCESS_WEBHOOK }}
+      SLACK_GHA_CANCELLED_WEBHOOK: ${{ secrets.SLACK_GHA_CANCELLED_WEBHOOK }}
+      SLACK_GHA_FIXED_WEBHOOK: ${{ secrets.SLACK_GHA_FIXED_WEBHOOK }}
+      SLACK_GHA_FAILURE_WEBHOOK: ${{ secrets.SLACK_GHA_FAILURE_WEBHOOK }}
+
+  failed-workflow:
+    name: Failed workflow tasks
+    runs-on: ubuntu-24.04
+    permissions:
+      actions: write
+    needs: [ slack-notifications ]
+    if: |
+      always() &&
+      github.repository == 'WordPress/wordpress-develop' &&
+      github.event_name != 'pull_request' &&
+      github.run_attempt < 2 &&
+      (
+        contains( needs.*.result, 'cancelled' ) ||
+        contains( needs.*.result, 'failure' )
+      )
+
+    steps:
+      - name: Dispatch workflow run
+        uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          retries: 2
+          retry-exempt-status-codes: 418
+          script: |
+            github.rest.actions.createWorkflowDispatch({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              workflow_id: 'failed-workflow.yml',
+              ref: 'trunk',
+              inputs: {
+                run_id: `${context.runId}`,
+              }
+            });